Test tasks * Test tasks with several correct answers 1. In monohybrid crossing, first generation hybrids are phenotypically and genotypically uniform - Mendel's law: 1) 1; 2) 2; 3) 3; 4) 4. 2. *Monoheterozygote is: 1) Aa; 2) AA; 3) AaBB; 4) Aavv; 5) aa; 6) AABB; 7) AaBb. 3. *Analyzing crossing is: 1) ♀Aa × ♂Aa; 2) ♀Aa × ♂aa; 3) ♀aa × ♂aa; 4) ♀aa × ♂Aa. 4. *Possible genotypes of offspring from crossing a polled (dominant trait) heterozygous cow with a horned bull: 1) all bb; 2) BB; 3) Bb; 4) all BB; 5) bb. 5. In an analysis cross, an F1 hybrid is crossed with a homozygote: 1) dominant; 2) recessive. 6. Crossing two heterozygotes (complete dominance) in the offspring there will be a splitting phenotype: 1) 9: 3: 3: 1; 2) 1:1; 3) 3:1; 4) 1:2:1. 7. The set of genes in a cell: 1) genotype; 2) genome; 3) karyotype; 4) phenotype; 5) gene pool. 8. *A trait is called dominant if: 1) is inherited in F1 hybrids 2) appears in heterozygotes; 3) does not appear in heterozygotes; 4) occurs in most individuals in the population. 9. Phenotype splitting in F2 with incomplete dominance in a monohybrid cross: 1) 9:3:3:1; 2) 1:1; 3) 3:1; 4) 1:2:1. 10. *The gray color of a rabbit's coat dominates over the white one. Gray rabbit genotype: 1) aa; 2) AA; 3) Aa; 4) AB. 11. As a result of crossing strawberry plants (incomplete dominance - red, white and pink fruit colors) with genotypes Aa and aa, the phenotypic ratio of the offspring is: 1) 1 red: 1 white; 2) 1 red: 1 pink; 3) 1 white: 1 pink; 4) 1 red: 2 pink: 1 white. 12. As a result of crossing chickens (incomplete dominance: black–blue–white plumage color) with genotypes Aa and Aa, the phenotypic ratio of offspring is: 1) 1 black: 1 white; 2) 3 black: 1 blue; 3) 3 black: 1 white; 4) 1 black: 2 blue: 1 white; 5) 1 blue: 1 white; 6) 3 blue: 1 white. 13. *Dominant homozygote is: 1) AaBB; 2) aabb; 3) AABB; 4) AABb; 5) AABBCC. 14. Gamete ABCD is formed by the genotype: 1) AabbCcDD; 2) AABbCcdd; 3) AaBbccDd; 4) aaBbCCDd. 15. *Drosophila has a black (recessive trait) body and normal wings (dominant trait) - genotype: 1) AABB; 2) AaBb; 3) aabb; 4) AaBB; 5) aaBb; 6) AABb; 7) Aabb; 8) aaBB. 16. *A rabbit has shaggy (dominant trait) white (recessive trait) fur – genotype: 1) AAbb; 2) AaBb; 3) aabb; 4) AaBB; 5) aaBb; 6) AABb; 7) Aabb; 8) aaBB. 17. *Peas have tall plants (dominant trait) and red flowers (dominant trait) - genotype: 1) aabb; 2) AABb; 3) Aabb; 4) AABB; 5) AaBb; 6) AaBB; 7) Aabb. 141 3.7. Basic patterns of variability Questions for repetition and discussion 1. What processes lead to combinative variability? 2. What is the basis for the uniqueness of each living organism at the level of genotype and phenotype? 3. What environmental factors can activate the mutation process and why? 4. How does the inheritance of somatic mutations differ from generative ones and what is their significance for the organism and species? 5. What mechanisms can you name for the movement of transposable elements throughout the genome? 6. Why does human activity increase the mutagenic effect of the environment? 7. What biological significance can transformation of the phenotype have without changing the genotype? 8. Why are modifications generally beneficial to the body? Test tasks 1. Phenotype is a set of external and internal characteristics of an organism. Consider Figure 3.108. Identify differences in phenotype. Make suggestions about the reasons for the differences in phenotypes of individuals of the same species. 2. Observations of Drosophila metamorphosis showed: a) if a little silver nitrate is added to the food of Drosophila larvae, Fig. 3.98. Variability of horns: yellow individuals are produced, despite their homozygosity for the dominant gene for gray body color (AA); b) in individuals homozygous for the recessive wing rudimentary gene (bb), at a temperature of 15°C the wings remain rudimentary, and at a temperature of 31°C normal wings grow. What can you say based on these facts about the relationship between genotype, environment and phenotype? Does the transformation of a recessive gene into a dominant one occur in these cases or vice versa? 142 3. Any sign can vary within certain limits. What is a reaction norm? Give examples of characteristics of organisms with broad and narrow reaction norms. What determines the breadth of a reaction norm? 4. Calculate the average value (M) and construct a variation curve using the following data (Table 3.8; 3.9). Table 3.8. Variability in the number of reed flowers in a chrysanthemum inflorescence Number of flowers in 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 inflorescences Number of inflorescences 1 3 6 25 46 141 529 129 47 30 12 12 8 6 9 Table 3.9. Variability of the number of bone rays in the shutter fin of the flounder number of rays in 47 48 49 50 51 52 52 53 54 55 57 58 58 59 60 61 Self number of individuals 2 5 13 23 58 96 134 127 111 74 37 16 4 2 1 5. In the Chernobyl region after After the disaster at the nuclear power plant, mutant animals began to appear, and the incidence of thyroid cancer in people increased. What do these facts indicate? Why do mutant fish with huge heads, no scales, one eye, and no color appear in the rivers of large cities polluted by industrial waste? Give an explanation for this phenomenon. 6. Consider Figure 3.99. Body weight in cattle, as in other animals, is a typical quantitative trait. The development of quantitative traits strongly depends on the influence of Fig. 3.99. Two yearling bulls under environmental conditions. Establish the ages that originated from the same type of variability that led to the father, but were raised under different conditions to change the body weight of these bull calves, one of which received food in excess, and the other was fed very sparingly. 143 7. Consider the different shapes of arrowhead leaves, (Fig. 3.100), which is a classic example of modification variability. Determine what causes the differences in leaf shape in arrowhead plants grown in different conditions. 8. Consider the changes in hair color of an ermine rabbit under the influence of different temperatures (Fig. 3.101). Determine the type of variability. Rice. 3.100. Shape of arrowhead leaves during development in different environments Fig. 3.101. Changes in the color of the fur of the Himalayan rabbit under the influence of different temperatures Laboratory workshop 1. A series of multiple alleles - a pattern of gray spots on clover leaves. Get acquainted with the herbarium of clover leaves and trace the pattern of inheritance of the trait of gray spots. The gene that determines this trait is represented by the eight most common alleles. Compare the drawing on the herbarium sheet with the drawings shown in the diagram (Fig. 3.102) and determine the genotype. There is incomplete dominance. It is impossible to determine the genotype of only those forms where the spot patterns determined by the two alleles merge or there is complete dominance. For example, VBVH and VHVH have the same phenotype, VBVP and VBVB also do not differ phenotypically, since VB is dominant over VH and VP; VFVP and VFVL are indistinguishable from VFVF due to the fusion of patterns. Heterozygotes with v also do not differ from dominant homozygotes. ! Sketch the specimens offered to you and determine their genotypes or phenotypic radicals, write down the symbols. Make a series of all the alleles encountered. 144 Fig. 3.102. Scheme of patterns of gray spots on clover leaves indicating the genotype (vv - no spot; VV - solid ^-shaped spot; VHVH - solid high ^-shaped spot; VBVB - ^-shaped spot with a break; VBhVBh - high ^-shaped spot with gap; VPVP - ^-shaped spot in the center; VFVF - solid triangular spot on the base; VLVL - solid small triangular spot on the base 2. Determination of an individual's ability to perceive the bitter taste of phenylthiourea (PTM). Using tweezers, place first a control and then an experimental strip of filter paper on the back of the tongue, determine your individual ability (inability) to perceive the bitter taste of PTM, i.e. sign of FTM+ or FTM-. Make a conclusion about your possible genotype, keeping in mind that the FTM+ trait is controlled by the dominant gene (T). Conditionally considering the student group as a separate population, determine the population frequency of the trait FTM+ (or FTM-) as the proportion of the number of individuals who are carriers of the trait in the total number of those surveyed. Calculate the genetic structure of the population (frequency of allelic genes and possible genotypes) using the Hardy-Weinberg formula: p² + 2pq + q² = 1, where p² is the frequency of homozygotes for the dominant allele (TT genotype), 2pq is the frequency of heterozygotes (Tt), q² – frequency of homozygotes for the recessive allele (tt) in the study population. When calculating the frequencies of the dominant (T) and recessive allele (t) present in the population, the formula p + q = 1 should be used. 145 Test tasks * Test tasks with several correct answers 1. Chemical compounds that induce mutations: 1) metagenes; 2) methylenes; 3) mutagens. 2. *The main mechanisms of the mutation process are violations of the following matrix processes: 1) translation; 2) replication; 3) transcriptions; 4) reparations. 3. A non-inherited change is called: 1) reversion; 2) isolation; 3) modification. 4. *High variability of quantitative traits is due to: 1) the polygenic nature of inheritance; 2) the influence of environmental factors; 3) genotypic heterogeneity; 4) homozygotization during the selection process. 5. *Genetic activity of the following genetic factors has been revealed: 1) electric current; 2) X-ray radiation; 3) gamma radiation; 4) ultraviolet radiation; 5) extreme temperatures. 6. Inherited from parents to descendants: 1) trait; 2) modification; 3) reaction norm; 4) phenotype; 5) modification variability. 7. The form of variability, as a result of which a left-handed blue-eyed child was born to right-handed, cross-eyed parents: 1) mutational; 2) combinative; 3) modification; 4) random phenotypic. 8. The form of variability, as a result of which, with the onset of winter, the animal experienced a change in color and thickness of hair: 1) mutation; 2) combinative; 3) modification; 4) random phenotypic. 9. The form of variability, as a result of which a child with six fingers was born in a family of five-fingered parents (a recessive trait): 1) mutation; 2) combinative; 3) modification; 4) random phenotypic. 10. *The reason for the increase in the frequency (occurrence) of several pathological alleles in the human population: 1) an increase in the level of radiation contamination; 2) immigration from areas with unfavorable environmental conditions; 3) increasing the birth rate; 4) increase in life expectancy; 5) improving the level of medical care. 11. A characteristic feature of modifications, in contrast to mutations: 1) material for evolution; 2) their formation is accompanied by a change in the genotype; 3) usually useful; 4) are inherited. 12. In adult ermine rabbits living in natural conditions, most of the body has white hair, and the tail, ears and muzzle are black, which is due to the difference in body areas in skin temperature - this is a manifestation of a form of variability: 1) mutational; 2) combinative; 3) modification; 4) random phenotypic. 13. A form of variability, as a result of which, with the onset of puberty, the timbre of the young man’s voice changed and a mustache and beard appeared: 1) mutational; 2) combinative; 3) modification; 4) random phenotypic. 14. Type of a typical variation curve: 1) straight line; 2) dome-shaped curve; 3) exhibitor; 4) circle. 15. *A persistent increase in the frequency of one of the dominant genes in an animal population is associated with the following most probable reasons: 1) changes in living conditions; 2) an increase in the birth rate; 3) the migration of some animals; 4) extermination of animals by humans; 5) lack of natural selection. 146 Part 4. POPULATION-SPECIES LEVEL OF ORGANIZATION Organic evolution is an objective process. A population is an elementary evolutionary unit. The main characteristics of the population as an ecological-genetic system (population area, number of individuals in the population, age composition, sex composition, basic morpho-physiological characteristics of the population, genetic heterogeneity of the population, genetic unity of the population). Mutations of various types are elementary evolutionary material. Genetic processes in populations. An elementary evolutionary phenomenon. Elementary factors of evolution. Mutation process. Population waves. Insulation. Genetic-automatic processes. Natural selection. The formation of adaptations is the result of natural selection. Classification and mechanism of adaptation. The relative nature of adaptations. Species is the main stage of the evolutionary process. Concept, criteria and structure of the type. Speciation is the result of microevolution. The main paths and methods of speciation. Patterns of macroevolution. Evolution of ontogenesis (integrity and stability, embryonication and autonomization of ontogenesis, ontogenesis is the basis of phylogeny). Evolution of phylogenetic groups (forms of phylogeny, main directions of evolution, extinction of groups and its causes). Evolution of organs and functions. Evolutionary progress. Origin and evolution of man. 4.1. Organic evolution is an objective process. Test tasks 1. One of the proofs of evolution is the unity of the organic world, in which there are a number of organisms that occupy an intermediate position between large systematic groups - transitional forms. Figure 4.1 shows some of the currently existing transitional forms of organisms. Get to know these organisms and indicate in their structure the signs of different types of organization. 2. The skeleton of the limbs of amphibians, reptiles, birds and mammals, despite the rather large differences in the appearance of the limbs and the function they perform, turns out to be constructed similarly (Fig. 4.2). What does the similarity in the structure of limbs that perform very different functions in vertebrates indicate? 147 Fig. 4.1. Currently existing transitional forms: 1 – horseshoe crab, occupying an intermediate position between modern typical arthropods and fossil trilobites; 2 – peripatus, bearing signs of arthropods and annelids; 3 – euglena, combining the characteristics of animals and plants; 4 – horseshoe crab larva, similar to trilobite larva; 5 - the crawling ctenophore combines, along with the characteristics of coelenterates, the characteristics of flatworms 3. In the structure of almost any organism one can find organs or structures that are relatively underdeveloped and have lost their former significance in the process of phylogenesis - these are rudimentary organs. Figure 4.3 shows the rudimentary hind limbs of a python, barely noticeable outgrowths of the rudiments of wings in a kiwi, and the rudiments of the pelvic bones of cetaceans. What do these organs indicate? Rice. 4.2. Homology of the forelimbs of vertebrates (salamander, sea turtle, crocodile, bird, bat, whale, mole, human) homologous parts are designated by the same letters and numbers 4. Among animals, one of the most striking relict forms is the hatteria - the only representative of an entire subclass of reptiles (Fig. . 4.4). It reflects the features of reptiles that lived on Earth in the Mesozoic. 148 Another well-known relic is the lobe-finned fish Coelacanth, which has been preserved little changed since the Devonian. Among plants, ginkgo can be considered a relic. The appearance of this plant gives an idea of the tree forms that became extinct in the Jurassic period. What do relict forms indicate? 5. Fossil transitional forms support the existence of kinship among systematic groups of animals. Complete Table 4.1 with some characteristics of protobirds in comparison with reptiles and true birds. Rice. 4.3. Examples of vestigial organs (A – hind limbs of a python; B – kiwi wing; C – elements of the pelvic girdle of a right whale) 6. Can Archeopteryx be considered a transitional form between the class of reptiles and real birds and why? What is the significance of Archeopteryx for proving the evolution of organic nature (Fig. 4.5)? List the transitional forms known to you. Why do intermediate forms not provide sufficient evidence for evolution? 7. Bird embryos at the early stages of embryonic development secrete ammonia as the final product of nitrogen metabolism, at later stages urea, and at the last stages of development - uric acid. Similarly, in frog tadpoles the end product of metabolism is ammonia, and in adult amphibians it is urea. How to explain these facts? Rice. 4.4. Relict organisms 1 – hatteria, 2 – coelacanth; 3 – possum; 4 – ginkgo 149 Table 4.1. Comparative characteristics of some characteristics of reptiles, Archeopteryx and real birds Organ systems and Reptiles Archeopteryx Real birds life processes Scales Feathers Forelimbs Presence of teeth Tail vertebrae Heart Ability to fly Lifestyle Reproduction 8. The study of the embryonic development of higher, terrestrial vertebrates showed that they have the formation and Some organs that have no significance in an adult animal, but are quite similar to the organs that characterize adult fish, reach a certain level of development. Consider Figure 4.6 and answer, what does the fact of the formation of parts of the gill apparatus in the embryos of terrestrial vertebrates indicate? 9. How can one prove the objectivity of the process of evolution of life on Earth? Rice. 4.5. Imprints of skeletal bones and feathers of Archeopteryx 10. In front of you is a horse, a mouse, a turtle, a butterfly, a pine tree. What methods can most reliably establish the relationship of these forms? 150
1. What is the role of the genotype and environmental conditions in the formation of the phenotype? Give examples.
Some traits are formed only under the influence of the genotype and their manifestation does not depend on the environmental conditions in which the organism develops. For example, in a person who has genes I A and I B in his genotype, blood group IV is formed, regardless of living conditions. At the same time, height, body weight, the number of red blood cells in the blood and many other characteristics depend not only on the genotype, but also on environmental conditions. Therefore, organisms that have the same genotypes (for example, monozygotic twins) may differ from each other in phenotype.
In 1895, the French botanist G. Bonnier conducted the following experiment: he divided a young dandelion plant into two parts and began to grow them in different conditions - on the plain and high in the mountains. The first plant reached normal height, but the second one turned out to be dwarf. This experience shows that the formation of the phenotype (i.e., traits) is influenced not only by the genotype, but also by environmental conditions.
Another example illustrating the influence of the external environment on the manifestation of traits is the change in coat color in Himalayan rabbits. Usually at 20°C their fur all over their body is white, with the exception of black ears, paws, tail and muzzle. At 30°C, rabbits grow completely white. If you shave the hair on the side or back of a Himalayan rabbit and keep it at an air temperature below 2°C, then instead of white wool it will grow black.
2. What is modification variability? Give examples.
Modifying variability is a change in phenotype under the influence of environmental factors that occurs without changing the genotype within the normal reaction limits.
For example, dandelion leaf length and shape vary significantly even within the same plant. It was noticed that the lower the temperature at which the leaves formed, the smaller they were and the larger the cutouts the leaf blade had. On the contrary, at higher temperatures larger leaves with small cutouts of the leaf blade are formed.
In an adult, depending on nutrition and lifestyle, body weight changes; in cows, milk yield can change; in chickens, egg production can change. In a person who finds himself high in the mountains, the content of red blood cells in the blood increases over time to provide the body cells with oxygen.
3. What is the reaction norm? Using specific examples, prove the validity of the statement that it is not the trait itself that is inherited, but its reaction norm.
The reaction norm is the limits of modification variability of a trait. Some traits, such as leaf length, plant height, animal body weight, cattle milk yield, and chicken egg production, have a wide reaction rate. Others, for example, the size of flowers and their shape, the color of seeds, flowers and fruits, the color of animals, the fat content of milk - have a narrower reaction norm.
The reaction rate is determined by the genotype and is inherited. For example, the more time a person spends in direct sunlight, the more melanin is synthesized in exposed areas of the skin and, accordingly, the darker its color. As you know, the intensity of tanning is not inherited, but is determined by the specific living conditions of a particular person. In addition, even in a Caucasian person who is constantly exposed to direct sunlight, the skin cannot synthesize the amount of melanin that is characteristic, for example, of representatives of the Negroid race. This example indicates that the range of variability of a trait (reaction norm) is predetermined by the genotype and it is not the trait itself that is inherited, but the ability of the organism to form a certain phenotype under the influence of environmental conditions.
4. Describe the main properties of modifications. Why is non-hereditary variability also called group variability? Certain?
Modifications have the following basic properties:
● Reversibility – with a change in external conditions, individuals change the degree of expression of certain characteristics.
● In most cases they are adequate, i.e. the degree of severity of a symptom is directly dependent on the intensity and duration of action of a particular factor.
● They have an adaptive (adaptive) nature. This means that in response to changing environmental conditions, an individual exhibits phenotypic changes that contribute to its survival.
● Mass distribution - the same factor causes approximately the same changes in individuals that are genotypically similar.
● Modifications are not inherited, because modification variability is not accompanied by a change in genotype.
Non-hereditary (modification) variability is called group variability, since certain changes in environmental conditions cause similar changes in all individuals of a particular species (mass property). Modification variability is also called definite, because modifications are adequate, predictable and accompanied by a change in the phenotype of individuals in a certain direction.
5. What statistical methods are used to analyze the variability of quantitative characteristics?
To characterize the degree of variability of quantitative characteristics, statistical methods such as constructing a variation series and a variation curve are most often used.
For example, the number of spikelets in complex ears of wheat of the same variety varies over a fairly wide range. If you arrange the ears in increasing order of the number of spikelets, you will get a variation series of the variability of this trait, consisting of individual variants. The frequency of occurrence of a particular variant in the variation series is not the same: the most common are ears with an average number of spikelets and less often those with more and less.
The distribution of variants in this series can be depicted graphically. To do this, the values of option (v) are plotted on the abscissa axis in the order of their increase, and on the ordinate axis – the frequency of occurrence of each option (p). A graphical expression of the variability of a trait, reflecting both the range of variations and the frequency of occurrence of individual variants, is called a variation curve.
6. How important is it in practice to know the norm of reaction of traits in plants, animals and humans?
Knowledge of the patterns of modification variability and reaction norms is of great practical importance, as it allows one to anticipate and plan many indicators in advance. In particular, creating optimal conditions for the implementation of the genotype makes it possible to achieve high animal productivity and plant yields. Knowledge of the norm of reaction of various human characteristics is necessary in medicine (it is important to know how certain physiological indicators correspond to the norm), pedagogy (upbringing and training taking into account the abilities and capabilities of the child), light industry (sizes of clothes, shoes) and many other areas of human activity .
7*. If a primrose, which under normal conditions has red flowers, is transferred to a greenhouse with a temperature of 30–35ºC and high humidity, the new flowers on this plant will already be white. If this plant is returned to relatively low temperature conditions (15-20ºC), it begins to bloom red flowers again. How can this be explained?
This is a typical example of modification variability. Most likely, an increase in temperature causes a decrease in the activity of enzymes that ensure the synthesis of red pigment in the petals, up to their complete inactivation (at 30–35ºС).
8*. Why in poultry farms is the daylight hours artificially extended for laying hens to 20 hours, and for broiler cockerels reduced to 6 hours per day?
Day length is an important factor influencing the sexual behavior of birds. Increasing the duration of daylight hours activates the production of sex hormones - thus, laying hens are stimulated to increase egg production. Short daylight hours cause a decrease in sexual activity, so broiler cockerels move less, do not fight with each other, and direct all the body’s resources to increasing body weight.
*Tasks marked with an asterisk require students to put forward various hypotheses. Therefore, when marking, the teacher should focus not only on the answer given here, but take into account each hypothesis, assessing the biological thinking of students, the logic of their reasoning, the originality of ideas, etc. After this, it is advisable to familiarize students with the answer given.
Patients with Edwards syndrome are born with low body weight (on average 2200 g).
Edwards syndrome is characterized by a combination of specific clinical manifestations: dolichocephaly, hypoplasia of the lower jaw and microstomia, narrow and short palpebral fissures, small low-lying ears, a characteristic flexion position of the fingers, a protruding occiput and other microanomalies (Fig. X.8). With the syndrome, defects of the heart and large vessels are almost constant, defects of the gastrointestinal tract, defects of the kidneys and genital organs are frequent. The life expectancy of patients with Edwards syndrome is sharply reduced. In the first year of life, 90% of patients die, by 3 years of age - more than 95%. The cause of death is defects of the cardiovascular system, intestines or kidneys.
All surviving patients have a deep degree of oligophrenia (idiocy)
Topic 26. Quantitative disorders of sex chromosomes
A change in the number of sex chromosomes can occur as a result of a violation of divergence in both the first and second divisions of meiosis. Violation of divergence in the first division leads to the formation of abnormal gametes: in women - XX and 0 (in the latter case, the egg does not contain sex chromosomes); in men - XY and 0. When gametes merge during fertilization, quantitative disturbances of the sex chromosomes occur (Table X. 1).
The incidence of trisomy X syndrome (47, XXX) is 1:1000 - 1:2000 newborn girls.
As a rule, physical and mental development in patients with this syndrome does not deviate from the norm. This is explained by the fact that two X chromosomes are activated in them, and one continues to function like in normal women. Changes in the karyotype, as a rule, are detected by chance during examination (Fig. X.9). Mental development is also usually normal, sometimes at the lower limits of normal. Only some women experience reproductive dysfunction (various cycle disorders, secondary amenorrhea, early menopause).
With tetrasomy X, high growth, a male-type physique, epicanthus, hypertelorism, flattened nasal bridge, high palate, abnormal growth of teeth, deformed and abnormally located auricles, clinodactyly of the little fingers, transverse palmar fold are noted. These women have described various menstrual irregularities, infertility, and premature menopause.
A decrease in intelligence from borderline mental retardation to various degrees of mental retardation is described in two thirds of patients. Among women with polysomy X, the incidence of mental illnesses (schizophrenia, manic-depressive psychosis, epilepsy) is increased.
Table: Possible sets of sex chromosomes during normal and abnormal course of the first meiotic division of gametogenesis
XXX triplo X | ||||
XO letal |
Klinefelter syndrome was named after the scientist who first described it in 1942. In 1959, P. Jacobe and J. Strong confirmed the chromosomal etiology of this disease (47, XXY) (Fig. X.10).
Klinefelter syndrome occurs in 1 in 500 to 700 newborn boys; in 1 - 2.5% of men suffering from oligophrenia (more often with shallow intellectual decline); in 10% of men suffering from infertility.
In the neonatal period, it is almost impossible to suspect this syndrome. The main clinical manifestations manifest during puberty. The classic manifestations of this disease are tall stature, eunuchoid physique, and gynecomastia, but all these symptoms occur simultaneously in only half of the cases.
An increase in the number of X chromosomes (48, XXXY, 49, XXXXY) in the karyotype leads to a greater degree of intellectual disability and a wider range of symptoms in patients.
Y-chromosome disomy syndrome was first described by co-authors in 1961; the karyotype of patients with this disease is 47, XYY (phc. X.11).
The frequency of this syndrome among newborn boys is 1:840 and increases to 10% in tall men (above 200 cm).
Most patients experience accelerated growth rates in childhood. The average height of adult men is 186 cm. In most cases, patients do not differ from normal individuals in physical and mental development. There are no noticeable deviations in the sexual and endocrine spheres. In 30-40% of cases, certain symptoms are observed - rough facial features, protruding eyebrows and bridge of the nose, enlarged lower jaw, high palate, abnormal growth of teeth with defects in dental enamel, large ears, deformation of the knee and elbow joints. Intelligence is either slightly reduced or normal. Emotional-volitional disorders are characteristic: aggressiveness, explosiveness, impulsiveness. At the same time, this syndrome is characterized by imitation and increased suggestibility, and patients most easily learn negative forms of behavior.
The life expectancy of such patients does not differ from the population average.
Shereshevsky-Turner syndrome, named after two scientists, was first described in 1925 by a Russian doctor, and in 1938 also clinically, but more fully, by C. Turner. The etiology of this disease (monosomy on the X chromosome) was discovered by Charles Ford in 1959.
The frequency of this disease is 1:2000 - 1:5000 newborn girls.
Most often, a cytogenetic study reveals karyotype 45, XO (Fig. X.12), however, other forms of X chromosome abnormalities are found (deletions of the short or long arm, isochromosome, as well as various
variants of mosaicism (30-40%).
A child with Shereshevsky-Turner syndrome is born only if the paternal (imprinted) X chromosome is lost (see this chapter - X.4). If the maternal X chromosome is lost, the embryo dies in the early stages of development (Table X.1).
Minimum diagnostic signs:
1) swelling of the hands and feet,
2) skin fold on the neck,
3) short stature (in adults - no more than 150 cm),
4) congenital heart defect,
5) primary amenorrhea.
With mosaic forms, a blurred clinical picture is noted. Some patients have normally developed secondary sexual characteristics and menstruation. Childbearing is possible in some patients.
Topic 27. Structural disorders of autosomes
The syndromes caused by an excess number of chromosomes (trisomy, polysomy) or the absence of a sex chromosome (monosomy X), i.e., genomic mutations, were described above.
Chromosomal diseases caused by chromosomal mutations are very numerous. More than 100 syndromes have been identified clinically and cytogenetically. We give one of these syndromes as an example.
The “cry of the cat” syndrome was described in 1963 by J. Lejeune. Its frequency among newborns is 1:45,000, sex ratio Ml:F1.3. The cause of this disease is the deletion of part of the short arm of chromosome 5 (5p-). It has been shown that only a small region of the short arm of chromosome 5 is responsible for the development of the full clinical syndrome. Occasionally, mosaicism due to deletion or the formation of ring chromosome-5 is observed.
The most characteristic symptom of this disease is the specific crying of newborns, similar to a cat's cry. The occurrence of a specific cry is associated with changes in the larynx - narrowing, softness of the cartilage, swelling or unusual folding of the mucous membrane, reduction of the epiglottis. These children often exhibit microcephaly, low-lying and deformed ears, microgenia, moon-shaped face, hypertelorism, epicanthus, Mongoloid eye shape, strabismus and muscular hypotonia. Children are sharply behind in physical and mental development.
Diagnostic signs such as “cat cry”, moon-shaped face and muscle hypotonia disappear completely with age, while microcephaly, on the contrary, becomes more obvious, and mental retardation also progresses (Fig. X.13).
Congenital malformations of internal organs are rare; the heart is most often affected (ventricular and atrial septal defects).
All patients have severe mental retardation.
Life expectancy in patients with 5p syndrome is significantly higher than in patients with autosomal trisomies.
Annex 1
Test your knowledge
1. Define the term “variability.”
2. Let us assume that in nature there is only variability, and there is no heredity. What would be the consequences in this case?
3. What mechanisms are the sources of combinative variability?
4. What is the fundamental difference between phenotypic and genotypic variability?
5. Why is non-hereditary variability called group or specific?
6. How is the influence of environmental factors reflected on the manifestation of qualitative and quantitative characteristics?
7. What could be the biological significance of the transformation of the phenotype under the influence of environmental factors without changing the genotype?
8. By what principles can mutations be classified?
9. What mechanisms may underlie the appearance of mutations in organisms?
10. What are the differences in the inheritance of somatic and generative mutations? What is their significance for an individual organism and an entire species?
11. What environmental factors can activate the mutation process and why?
12. What environmental factors can have the greatest mutagenic effect?
13. Why does human activity increase the mutagenic effect of the environment?
14. How are mutagens used in the selection of microorganisms, plants and animals?
15. What measures are required to protect people and nature from the effects of mutagens?
16. What mutations can be called lethal? What makes them different from other mutations?
17. Give examples of lethal mutations.
18. Are there harmful mutations in humans?
19. Why is it necessary to know the structure of human chromosomes well?
20. What set of chromosomes is found in Down syndrome?
21. List the chromosomal disorders that can occur under the influence of ionizing radiation?
22. What types of gene mutations do you know?
23. How do gene mutations differ from genomic ones?
24. What type of mutation is polyploidy?
Appendix 2
Test on the topic "Variability. Mutations and their properties" |
Option 1 |
B. Genotypic variability
A. Variational series
B. Variation curve
B. Norm of reaction
D. Modification
A. Phenocopies
B. Morphoses
B. Mutations
G. Aneuploidy
B. Mutational variability
G. Polyploidy
A. Chemical
B. Physical
B. Biological
D. There is no correct answer.
A. Somatic
B. Gene
B. Generative
G. Chromosomal
A. Deletion
B. Duplication
B. Inversion
G. Translocation
A. Monosomy
B. Trisomy
B. Polysomy
G. Polyploidy
A. Modifications
B. Morphoses
B. Phenocopies
G. Mutations
10.Tanning is an example...
A. Mutations
B. Morphosis
B. Phenocopies
D. Modifications
Option 2 |
B. Mutational variability
D. Phenotypic variability
B. Mutational variability
D. Modification variability
A. Combinative variability
B. Gene mutation
B. Chromosomal mutation
G. Genomic mutation
4. Rotating a section of a chromosome by 1800 is called...
A. Translocation
B. Duplication
B. Deletion
G. Inversion
A. Polyploidy
B. Polysomy
B. Trisomy
G. Monosomy
A. Modifications
B. Morphoses
B. Phenocopies
G. Mutations
A. Polyploidy
B. Polysomy
B. Deletion
G. Trisomy
A. Chemical
B. Biological
B. Physical
D. There is no correct answer.
A. Somatic
B. Neutral
B. Genomic
D. There is no correct answer.
A. Modifications
B. Phenocopies
V. Morphosis
G. Polyploidy
Option 3 |
A. Modification
B. Phenotypic
B. Genotypic
G. Non-hereditary
A. Physical
B. Biological
B. Chemical
D. There is no correct answer.
A. Combinative variability
B. Mutational variability
A. Monosomy
B. Trisomy
B. Polysomy
G. Polyploidy
A. Phenocopies
B. Mutations
B. Modifications
G. Morphoses
A. Somatic
B. Generative
B. Useful
G. Genetic
A. Polysomy
B. Trisomy
B. Polyploidy
G. Monosomy
A. Deletion
B. Duplication
B. Inversion
G. Translocation
A. Point
B. Gene
B. Genomic
D. There is no correct answer.
A. Phenocopies
B. Modifications
V. Morphosis
D. There is no correct answer.
Answers to the test on the topic "Variability. Mutations, their properties" |
Answers to Option 1 |
1. The basis for the diversity of living organisms is:
A. Modification variability
*B. Genotypic variability
B. Phenotypic variability
D. Non-hereditary variability
2.The boundaries of phenotypic variability are called...
A. Variational series
B. Variation curve
*IN. Norm of reaction
D. Modification
3. Non-hereditary changes in the genotype that resemble hereditary diseases are...
*A. Phenocopies
B. Morphoses
B. Mutations
G. Aneuploidy
4.Changes in gene structure underlie...
A. Combinative variability
B. Modification variability
*IN. Mutational variability
G. Polyploidy
5. Radiation is... a mutagenic factor
A. Chemical
*B. Physical
B. Biological
D. There is no correct answer.
6. Mutations that affect only part of the body are called...
*A. Somatic
B. Gene
B. Generative
G. Chromosomal
7.Loss of a section of a chromosome is called...
*A. Deletion
B. Duplication
B. Inversion
G. Translocation
8. The phenomenon of loss of one chromosome is called...(2n-1)
*A. Monosomy
B. Trisomy
B. Polysomy
G. Polyploidy
9. A constant source of hereditary variability is...
A. Modifications
B. Morphoses
B. Phenocopies
*G. Mutations
10.Tanning is an example...
A. Mutations
B. Morphosis
B. Phenocopies
*G. Modifications
Answers to Option2 |
1. Variability that does not affect the genes of the organism and does not change the hereditary material is called ...
A. Genotypic variability
B. Combinative variability
B. Mutational variability
*G. Phenotypic variability
2.Indicate directional variability:
A. Combinative variability
B. Mutational variability
B. Relative variability
*G. Modification variability
3.Changes in the number of chromosomes are the basis...
A. Combinative variability
B. Gene mutation
B. Chromosomal mutation
*G. Genomic mutation
4. Rotating a section of a chromosome by 180 degrees is called...
A. Translocation
B. Duplication
B. Deletion
*G. Inversion
5. Shereshevsky-Turner syndrome can occur as a result of...
A. Polyploidy
B. Polysomy
B. Trisomy
*G. Monosomy
6. Non-hereditary changes in the genotype that occur under the influence of environmental factors are adaptive in nature and most often reversible - this is...
*A. Modifications
B. Morphoses
B. Phenocopies
G. Mutations
7. The phenomenon of changing the number of chromosomes, a multiple of the haploid set, is called...
*A. Polyploidy
B. Polysomy
B. Deletion
G. Trisomy
8. Alcohol is... a mutagenic factor
*A. Chemical
B. Biological
B. Physical
D. There is no correct answer.
9. Mutations that lead to increased resistance of the body are called...
A. Somatic
B. Neutral
B. Genomic
*G. There is no correct answer
10. An increase in red blood cells in the blood with a lack of oxygen is an example...
*A. Modifications
B. Phenocopies
V. Morphosis
G. Polyploidy
Answers to Option3 |
1.Indicate non-directional variability:
A. Modification
B. Phenotypic
*IN. Genotypic
G. Non-hereditary
2. Colchicine is... a mutagenic factor
A. Physical
B. Biological
*IN. Chemical
D. There is no correct answer.
3. Crossover is a mechanism...
*A. Combinative variability
B. Mutational variability
B. Phenotypic variability
D. Modification variability
4. The phenomenon of acquiring one chromosome is called...(2n+1)
A. Monosomy
*B. Trisomy
B. Polysomy
G. Polyploidy
5. Non-hereditary changes in phenotype that occur under the influence of extreme environmental factors, are not adaptive in nature and are irreversible, are called...
A. Phenocopies
B. Mutations
B. Modifications
*G. Morphoses
6. Mutations that occur in germ cells (and therefore are inherited) are called...
A. Somatic
*B. Generative
B. Useful
G. Genetic
7. Klinefeltre's syndrome can result from...
A. Polysomy
*B. Trisomy
B. Polyploidy
G. Monosomy
8. The transfer of an entire chromosome to another chromosome is called...
A. Deletion
B. Duplication
B. Inversion
*G. Translocation
9. Mutations associated with changes in the structure of chromosomes are called...
A. Point
B. Gene
B. Genomic
*G. There is no correct answer
10.Loss of limbs is an example...
A. Phenocopies
B. Modifications
*IN. Morphosis
D. There is no correct answer.
Appendix 3
test on the topic “Variability”.
Task No. 1
Organisms adapt to specific environmental conditions without changing the genotype due to variability
a) mutational
b) combinative
c) relative
d) modification
2. Do leaves plucked from one tree have variability?
a) mutational
b) combinative
c) modification
d) all leaves are the same, there is no variability
3. The role of modification variability
a) leads to a change in genotype
b) leads to recombination of genes
c) allows you to adapt to different environmental conditions
d) doesn't matter
4. Modification variability as opposed to mutational variability:
a) usually manifests itself in most individuals
b) characteristic of individual individuals of the species
c) associated with gene changes
d) is hereditary
5. An increase in body weight in domestic animals due to changes in diet is classified as variability:
a) modification
b) cytoplasmic
c) genotypic
d) combinative
Task No. 2
Fill in the table with numbers.
Modification variability | Mutational variability |
|||||||||||||||||||
What sign relates to these mutations?
1. The phenotype is within the normal range of reaction.
2. Chromosomes do not undergo changes.
3. The form of variability is group.
4. the law of homological series of hereditary variability.
5. Useful changes lead to victory in the struggle for existence.
6. Promotes survival.
7. DNA molecules are not subject to variability.
8. Selecting factor – change in environmental conditions.
9. Inheritance of characteristics.
10. Increases or decreases productivity.
Task No. 3
Fill in the table with numbers.
Modification variability | Mutational variability |
|||||||||||||||||||
1. They arise gradually and have transitional forms.
2. They arise under the influence of the same factor.
3. They appear intermittently.
4. May occur repeatedly.
5. Not passed on from generation to generation.
6. Reversible.
7. The same and different genes can mutate under the influence of the same factor.
8. Passed on from generation to generation.
9. The basis of existence is phenotype.
10. The basis of existence is the genotype.
Task No. 4
Match:
I By level of occurrence | 1.Generative |
II By place of origin | 2.Biochemical |
III By type of allelic relationships | 3.Lethal |
IV By influence on the viability of an individual | 4. Spontaneous |
V By nature of manifestation | 5.Amorphous |
VI According to phenotypic origin | 6.Genomic |
VII By origin | 7.Induced |
8. Dominant |
|
9.Intermediate |
|
10. Harmful |
|
11.Somatic |
|
12.Antimorphic |
|
13.Neutral |
|
14.Physiological |
|
15.Recessive |
|
16.Hypomorphic |
|
17.Useful |
|
18.Morphological |
|
19.Chromosomal |
|
21.neomorphic |
To I
To II relate _______________________
To III _
To IV relate _______________________
To V relate _______________________
To VI relate ______________________
To VII relate ______________________
Genotype- a set of hereditary characteristics and properties received by an individual from its parents. As well as new properties that appeared as a result of gene mutations that the parents did not have. The genotype is formed by the interaction of two (egg and sperm) and represents a hereditary development program, being an integral system, and not a simple sum of individual genes. The integrity of the genotype is the result of development, during which all genes were in close interaction with each other and contributed to the preservation of the species, acting in favor of stabilizing selection. Thus, a person’s genotype determines (determines) the birth of a child, a hare’s offspring will be represented by hares, and only a sunflower will grow from a sunflower.
Genotype– it’s not just the sum of genes. The possibility and form of gene manifestation depend on environmental conditions. The concept of environment includes not only the conditions surrounding the cell, but also the presence of other genes. Genes interact with each other and, once in one, can greatly influence the manifestation of the action of neighboring genes.
Phenotype- the totality of all the signs and properties of an organism that have developed in the process of individual development of the genotype. This includes not only external signs (skin color, hair, ear or nose shape, flower color), but also internal ones: anatomical (body structure and relative arrangement of organs), physiological (shape and size of cells, structure of tissues and organs), biochemical ( protein structure, enzyme activity, concentration of hormones in the blood). Each individual has its own characteristics of appearance, internal structure, nature of metabolism, functioning of organs, i.e. your phenotype, which was formed under certain environmental conditions.
If we consider the results of self-pollination F2, we can find that plants grown from yellow seeds, although externally similar and having the same phenotype, have a different combination of genes, i.e. different genotype.
Concepts genotype and phenotype– very important in . The phenotype is formed under the influence of the genotype and environmental conditions.
It is known that the genotype is reflected in the phenotype, and the phenotype is most fully manifested under certain environmental conditions. Thus, the manifestation of the gene pool of a breed (variety) depends on the environment, i.e. conditions of detention (climatic factors, care). Often varieties developed in some areas are not suitable for cultivation in others.
QUESTIONS AND TASKS FOR REVIEW
Question 1. Give examples of the influence of the environment on the manifestation of a trait.
Sometimes, under the influence of certain environmental factors, stable characteristics can also change. Thus, in rabbits homozygous for the recessive ermine color gene, having a white body and black ears, tail, end of the muzzle and ends of the paws, the color pattern can be changed under the influence of temperature. N.A. Ilyin shaved areas of white and black hair from ermine rabbits and created conditions of low or high temperature. Depending on the temperature, white or black hair grew on the shaved areas of the body. For each part of the body, a threshold of irritation was set - the temperature above which white hair developed, and below which black hair developed. Thus, on the side of a rabbit at temperatures below 2 ° C, black wool grew, on the ear at temperatures above 30 ° C - white wool, etc. Thus, it is not the pattern of the rabbit that is inherited, but the ability or inability, depending on the temperature, to form pigment in hair When environmental conditions change, sometimes a trait changes in the same way as under the influence of genes, but the resulting characteristics are not hereditary. Such changes are called phenocopies. For example, in chickens, the congenital defect of taillessness is inherited, but in some cases it is caused by the influence of the external environment during the incubation period.
Question 2. Give examples that prove the non-heritability of changes in a trait caused by environmental conditions.
Many traits change during growth and development under the influence of environmental factors. Such changes in characteristics are not inherited.
The lotus and water chestnut have underwater and above-water leaves of different shapes: the lotus in the water has long, thin, lanceolate-shaped leaves, while the water chestnut has rugged, pinnate leaves.
Under the influence of ultraviolet rays, all people (if they are not albinos) develop a tan due to the accumulation of melanin pigment granules in it.
Thus, each type of organism reacts specifically to the action of a certain environmental factor, and the reaction (change in character) turns out to be similar in all individuals of a given species.
Question 3. Why is non-hereditary variability called group or specific?
Modifications are always associated with a specific environmental factor. For example, under the influence of ultraviolet radiation, the pigment melanin is synthesized and accumulated in human skin, and as a result of physical activity, the protein myoglobin is synthesized in muscle tissue, and never vice versa. In other words, phenotypic changes are determined by a given environmental factor. In addition, similar changes as a result of the action of the same environmental factor occur in all representatives of a given species, i.e. they are group changes.
Question 4. What is the reaction norm?
At the same time, the variability of a trait under the influence of environmental conditions is not unlimited. The degree of variation of a characteristic, or, in other words, the limits of variability, is called the reaction norm. The breadth of the reaction norm is determined by the genotype and depends on the significance of the trait in the life of the organism. A narrow reaction norm is characteristic of such important characteristics as, for example, the size of the heart or brain
Question 5. List and characterize the properties of modifications.
Modification variability is characterized by the following main properties: 1) non-heritability; 2) the group nature of the changes; 3) dependence of changes on the action of a certain environmental factor; 4) the dependence of the limits of variability on the genotype, i.e., with the same direction of changes, the degree of their expression in different organisms is different.
Question 6. Compare the properties of mutations and modifications. Comparative characteristics of forms of variability
QUESTIONS AND TASKS FOR DISCUSSION
Question 1. How is the influence of environmental factors reflected on the manifestation of qualitative and quantitative characteristics?
Environmental factors have a greater influence on the manifestation of qualitative than quantitative traits.
Question 2. What could be the biological significance of the transformation of the phenotype under the influence of environmental factors without changes in the genotype?
This biological phenomenon includes seasonal modifications. They, in turn, can be classified as environmental modifications. The latter represent adaptive changes in phenotype in response to changes in environmental conditions. Ecological modifications are phenotypically manifested in changes in the degree of expression of a trait. They can occur in the early stages of development and persist throughout life. An example is the different leaf shapes of the arrowhead, determined by the influence of the environment: arrow-shaped above-water, wide floating, ribbon-shaped underwater.
Question 3. How can the breadth of reaction norms affect adaptation to specific living conditions?
PROBLEM AREAS
Question 1. What are the differences in the inheritance of somatic and generative mutations? What is their significance for an individual organism and an entire species?
The primary role belongs to generative mutations that occur in germ cells. Generative mutations, causing changes in the characteristics and properties of the organism, can be detected if the gamete carrying the mutant gene participates in the formation of the zygote. If the mutation is dominant, then a new trait or property appears even in a heterozygous individual descended from this gamete. If the mutation is recessive, then it can appear only after several generations when it becomes homozygous. An example of a generative dominant mutation in humans is the appearance of blistering of the skin of the feet, cataracts of the eye, and brachyphalanxia (short fingers with insufficiency of the phalanges). An example of a spontaneous recessive generative mutation in humans is hemophilia in individual families.
Somatic mutations by their nature are no different from generative ones, but their evolutionary value is different and is determined by the type of reproduction of the organism. Somatic mutations play a role in organisms that reproduce asexually. Thus, in vegetatively propagated fruit and berry plants, a somatic mutation can produce plants with a new mutant trait. The inheritance of somatic mutations is currently becoming important for studying the causes of cancer in humans. It is assumed that for malignant tumors the transformation of a normal cell into a cancerous one occurs according to the type of somatic mutations.
Question 2. What mechanisms may underlie the appearance of mutations in living organisms?
Mutations appear constantly during processes occurring in a living cell. The main processes leading to the occurrence of mutations are DNA replication, DNA repair disorders and genetic recombination.
Question 3. What are the principles of classification of hereditary variability?
Variability can be non-hereditary and hereditary.
Hereditary variability is divided into combinative and mutational. Combinative variability is associated with recombination of parental genes.
Mutational variability is caused by mutations - stable changes in genetic material and, accordingly, an inherited trait.
APPLIED ASPECTS
Question 1. How can induced mutations caused in laboratory conditions be used to obtain traits that humans need from microorganisms?
A striking example of the use of chemical mutagens is the creation of polyploid plant varieties. People have always tried to breed those plants that had especially large fruits or produced a large harvest. In many cases, polyploids have these properties. As it turned out, these include many cultivated plants: wheat, oats, potatoes, sugar cane, plums, cherries, etc. Chemical mutagens made it possible to obtain polyploids artificially. For example, V.V. Sakharov obtained tetraploid buckwheat, a high-yielding variety with large seeds.
Question 2. What environmental factors can activate the mutation process in living organisms living in natural conditions?
To increase the frequency of mutations, it is necessary to influence cells with various mutagenic factors, such as:
1. Ultraviolet radiation;
2. Organic and inorganic compounds of natural origin (nitrogen oxides, nitrates, radioactive compounds, alkaloids).
Question 3. How can valuable traits and properties newly emerging as a result of combinative variability be consolidated?
Valuable traits that arise as a result of combinative variability are fixed in the course of natural and artificial selection.
TASKS
Question 1. Give examples of gene, chromosomal and genomic mutations in animals and plants.
An example of a genomic mutation is polyploidy. It is widespread in plants and much less common in animals (roundworms, silkworms, and some amphibians). Polyploid organisms, as a rule, are characterized by larger sizes and enhanced synthesis of organic substances, which makes them especially valuable for breeding work. Example: Down syndrome in humans is trisomy 21, with a total of 47 chromosomes in a cell. Mutations can be obtained artificially using radiation, x-rays, ultraviolet radiation, chemical agents, and heat.
Question 2. Give examples of signs characterized by a wide and narrow norm of reaction. Explain how they influence the adaptation of organisms to their environment.
Knowledge of the norm of the body’s reaction, the limits of its modification variability is of great importance in breeding practice when “designing” new forms of plants, animals and microorganisms useful to humans. This is especially important for agricultural practice, the goal of which is to increase the productivity of plants and animals by not only introducing new breeding forms - breeds and varieties, but also maximizing the capabilities of existing breeds and varieties. Knowledge of the patterns of modification variability is also necessary in medicine for the maintenance and development of the human body within the normal reaction limits.