chromosomal inheritance phenotypic genotype
When analyzing the patterns of inheritance, it is necessary to study three main processes:
- 1. self-reproduction of the cell and its elements;
- 2. distribution of chromosomes during gametogenesis and their subsequent combination during fertilization;
- 3. action of genes in individual development organism.
A gene, as a unit of heredity, has a number of properties:
- discreteness of action - the development of various traits is controlled by different genes located in different loci of chromosomes;
- stability - the transmission of hereditary information unchanged (in the absence of mutations);
- lability (instability) - the ability to mutate;
- specificity - each gene is responsible for the development of a particular trait;
- pleiotropy - one gene can be responsible for several traits. For example, Marfan's syndrome, characterized by "spider toes", a high arch of the foot, the development of an aortic aneurysm, is associated with a defect in the development of connective tissue;
- expressiveness - the degree of expression of a trait (polymerism);
- Penetrance - frequency of occurrence;
- The ability to interact with other non-allelic genes.
Genes operate at two levels: at the level of the genetic system itself, determining the state of the genes, their work, the rate of DNA replication, the stability and variability of genes, and at the level of the work of cells in the system of the whole organism. Thus, the genotype is an integral genetic system of an organism, and not a simple set of all its genes.
Mendel discovered the simplest mechanisms of gene interaction: dominance and incomplete dominance.
Much later, other types of allelic interaction of genes were studied - coding and overdominance. Codominance (more commonly called multiple allelism) is the definition of a trait by several groups of allelic genes. Codominance refers to the type of inheritance of blood groups.
Overdominance is a manifestation of a trait to a greater extent in heterozygous individuals.
Genes in the body enter into more complex non-allelic relationships, the most fully studied of which are polymerization, epistasis, complementarity.
Complementary interaction of genes is due to the joint manifestation of several pairs of non-allelic genes during the manifestation of a new trait. Using the example of the inheritance of the color of sweet pea flowers, one can understand the essence of the complementary action of genes. When crossing two races of this plant with red and white flowers, the hybrids of the second generation showed splitting of signs 9:7.
This result can be explained as follows: the formation of the anthocyanin pigment is determined by the dominant gene A, the absence of pigment - a;
The transition of the propigment to the pigment is determined by the enzyme, the synthesis of which is due to the dominant gene B, the absence of the enzyme - c.
The flowers will be colored only if the genotypes contain AB (AABB, AaBv, AABv, AaBB), if at least one gene is in a homozygous recessive state, the flowers will be white.
Epistasis is defined as the suppression of one non-allelic gene by another. Epistasis can be dominant or recessive. Genes that exhibit epistatic action are called suppressors. An example of dominant epistasis is the inheritance of coloration in pigs. When crossing white and black pigs of different breeds in the first generation, all pigs were white, and in the second generation there was a split in the ratio: 12/16 - white; 3/16 - black and 1/16 - red
An example of recessive epistasis is the Bombay phenomenon. A woman with the first and a man with the second blood group had a child with the fourth blood group. In the study of this case, an epistatic gene c was found that suppressed gene I B
Polymerism is a phenomenon when the manifestation of a particular trait depends on several dominant genes in different alleles. For example, when crossing red-grain wheat with the genotype A 1 A 1 A 2 A 2 with white-grain wheat with the genotype a 1 a 1 a 2 a 2, there were plants with different grain colors from bright pink (A 1 A 1 A 2 a 2) to pale pink (a 1 a 1 a 2 A 2
Thus, the interaction of genes has a multilevel and diverse character.
Lesson summary on the topic: The genotype as an integral system.
Interaction of genes.
The purpose of the lesson: formation of knowledge about the influence of genes on the phenotype of an organism; development of skills in working with genetic symbols.
Tasks:
generalize and deepen knowledge about the genotype as an integral, historically established system;
To reveal the manifestation of the relationship and interaction of genes with each other, affecting the manifestation of various features;
Continue the formation of skills to work with genetic symbols
The structure and main content of the lesson. Methods and methodological techniques.
1. Organizational moment.
2. Presentation of new material.
Question: What is a genotype?(Slide 3)
Genotype - this is a set of genes and their cytoplasmic carriers, which determine the development of hereditary traits and properties of the organism.
The real existence of a gene is proved by two groups of facts: a relatively independent combination during splitting and the ability to change - to mutate. Among the main properties of the gene is its ability to duplicate when doubling the chromosomes. Genes have significant stability, which determines the relative constancy of the genotype. There is a close interaction between genes, as a result of which the genotype cannot be considered as a simple mechanical sum of genes, but is a complex system that has developed in the evolution of organisms.
Question: What is the carrier of genes?(Slide 4)
The cytoplasmic carriers of genes are chromosomes, which include DNA and proteins. The basis of the properties of the gene listed above is the ability of DNA to self-replicate. The action of genes is based on its ability to determine protein synthesis through RNA. This mechanism is common at all stages of evolution.
When forming genetic ideas about the relationship between genes and a trait, it was assumed that each trait corresponds to a special hereditary factor that determines the development of its trait. However, direct and unambiguous links between a gene and a trait are actually the exception rather than the rule. It was found that there are a huge number of properties and traits of organisms that are determined by two, three, and even many pairs of genes, and, conversely, one gene often affects many traits. In addition, the action of a gene can be changed by the proximity of other genes or environmental conditions. Thus, it is not individual genes that act in ontogeny, but the entire genotype as an integral system with complex connections and interactions between genes.
What is gene interaction?
Gene Interaction - this is a joint action of several genes, leading to the appearance of a trait that is absent in the parents, or enhancing the manifestation of already existing traits.
Scheme: Interaction of genes. (Slide 5)
Gene Interaction
Allelic Non-allelic
1. Complete dominance 1. Complementarity
2. Incomplete dominance 2. Epistasis
3. Multiple allelism 3. Polymerism
4. Codominance
5. Overdominance.
Question: What is complete dominance?(Slide 6, 7)
Incomplete dominance? (Slide 8, 9)
Multiple allelism (Slide 10) - this is the phenomenon of the existence of more than two alternative allelic genes that have different manifestations in the phenotype.
(Slide 11)
p. 7, Animated table "Manifestation of multiple allelism"
Example 1 Blood groups in humans are determined by the combination of alleles A, B and 0 of the same gene I in the genotype.
Example 2. Coat color in rabbits: dark, white (albinism), ermine (alleles A (dark), A 1 (ermine), a (white)).
Example 3 The fruit fly has a series of alleles for the eye color gene, consisting of 12 members: cherry, red, coral, etc. to white, determined by the recessive gene.
Example 4 The coat color of a house mouse: A Y - yellow, A - gray, a t - dark back, beige abdomen, a - black. Allele A Y affects the viability of homozygotes A Y A Y .
Thus, multiple allelism characterizes the diversity of the gene pool of the whole species, i.e. is a species, not an individual trait.
Codominance (Slide 12) - the phenomenon of independent manifestation of both alleles in the heterozygous phenotype.
Example. (Slide 13) Interaction of alleles that determine the fourth blood group in humans.
A multiple series of alleles of gene I is known, which determines the sign of a blood group in humans. Gene I is responsible for the synthesis of enzymes that attach certain polysaccharides to proteins located on the surface of red blood cells. These polysaccharides determine the specificity of blood groups.
The alleles I A and I B encode different enzymes, the allele I 0 does not encode any, it is recessive with respect to I A and I B. and between I A and I B there is no dominant-recessive relationship.
People with IV blood group carry alleles I A and I B in their genotype, they synthesize two enzymes and form the corresponding phenotype.
overdominance (Slide 14) - a stronger manifestation of the trait in the heterozygote, and not in the homozygote.
Example. Drosophila has a recessive lethal gene, heterozygotes for which are more viable than dominant homozygotes.
Complementarity (additional action of genes) (Slide 15) - this is a phenomenon in which non-allelic genes complement each other's action, and a trait is formed only with the simultaneous action of both genes.
Example. The shape of the comb in chickens (task 1).
epistasis (Slide 16) - a type of interaction of non-allelic genes, in which one of the genes completely suppresses the action of another gene.
A gene that suppresses the action of another gene is called a gene - suppressor, inhibitor, epistatic gene. The suppressed gene is called hypostatic.
Epistasis can be dominant (gene - suppressor dominant) and recessive (gene - suppressor recessive). (Slide 17)
Example 1 Dominant epistasis (task 2). Pigmentation of plumage in chickens.
Example 1. Recessive epistasis (task 3). Coat coloration in house mice.
Group work of students with examples of gene interaction, followed by a discussion of the results.
Polymerism (Slide 18) - one of the types of interaction of non-allelic genes, in which the manifestation of a quantitative trait is influenced simultaneously by several genes. At the same time, the more dominant genes in the genotype that determine this trait, the brighter this trait is expressed - cumulative polymerism (accumulating). Non-cumulative polymer (non-accumulative) - the presence of at least one dominant gene in the genotype determines the development of the trait.
Polymeric genes are designated by the same letter of the Latin alphabet with a numerical index indicating the number of allelic pairs, for example, A 1 a 1; A 2 a 2 etc.
Electronic supplement to the textbook “Biology. Living systems and ecosystems”, page 7, Dictionary
(Slide 19)
Example 1. Cumulative polymer. (task 4). Human skin color
Example 1. non-cumulative polymer. (task 5). Leg feathering in chickens.
3. Consolidation and conclusions.
Thus, we see that as a result of the interaction of non-allelic genes, a deviation from Mendeleev splits is observed, and instead of the classical splitting of phenotype classes 9:3:3:1, 13:3, 9:3:4, 15:1 can be observed.
Let's see if the examples we have considered really contradict Mendeleev's laws. Let's fill in the table.
Table. The influence of the interaction of non-allelic genes on the ratio of phenotypic classes in F2 during dihybrid crossing. (Slide 20)
(Independent work students)
Type of gene interaction
Cleavage by phenotype
Genotypic composition of phenotypic classes
complementarity
Inheritance of the comb shape in chickens
Dominant epistasis
Inheritance of feather pigmentation in chickens.
3 I-cc white
1 iicc painted
recessive epistasis
Inheritance of coat color in house mice
9 A -C - agouti a 2 a 2 non-feathered
Conclusion: like wine from the table, splitting in some cases flows atypically. However, these deviations concern only phenotypic classes. Splitting according to genotypes in all cases occurs in full accordance with the laws established by Mendel. Thus, considering different kinds interaction of genes, we can assume that the genotype is a balanced system of interacting genes; the development of a trait is the result of the manifestation of several genes.
An example of the influence of one gene on several traits is:
Pleiotropy or multiple action of genes is the phenomenon of the simultaneous influence of one gene on several traits. Electronic supplement to the textbook “Biology. Living systems and ecosystems”, p. 7, Animated table "Multiple actions of genes"
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4. Homework : $ 43
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Slides captions:
From purely human relations, Giving life to the omnipresent course, Giving birth to both joy and sorrow, There are relations between a woman and a man. And you can say the opposite. Everything else, if you like, is derived from these relations. Vasily Fedorov.
Subject. The genotype as an integral system. Interaction of genes.
I need to figure it out myself. And to figure it out yourself, you need to think together... Boris Vasiliev
Objectives: 1. Know: types of gene interaction, genetic terminology; 2. Understand the essence of various gene interactions; 3. Be able to: operate with genetic concepts, explain the integrity of the genotype; 4. Apply terms and concepts in situations Everyday life. 5. Evaluate the results of gene interaction in terms of their significance for a particular organism.
Gene Trait Pleiotropic (from the Greek pleion - set and tropos - direction) or multiple action of a gene is the influence of one gene on the formation of several traits. Feature 1 Feature 3 2
Gene Trait Gene interaction is the influence of several genes on the development of one trait. Gene 1 Gene 3 2
Interaction of genes Non-allelic Allelic 1. Complementarity. 2. Epistasis. 3. Polymer. 1. Complete dominance. 3. Codominance. 2. Incomplete dominance.
Express - lottery! 1 2 3 4 5
Conclusions: 1. Genotype is a system of interacting genes. 2. The integrity of this system is characterized by the relationship and consistency of biochemical and physiological processes. 3. Both allelic and non-allelic genes located in different loci of the same and different chromosomes interact with each other.
Creative task. Burime. Create a poetic work using rhymes: 1. Heredity is responsibility. 2. Locus - focus. 3. Genotype - phenotype. 4. Once - epistasis. 5. Pleiotropy is a utopia. 6. Complementarity - gratitude. 7. Century - a person. Allowed: 1. Any sequence. 2. Use of rhymes with other genetic terms. Evaluation criteria: 1. Content. 2. Sympathy.
Complete dominance A - yellow peas a - green peas P ♀ AA ♂ aa yellow green gametes A a F 1 Aa yellow x
Incomplete dominance B – purple color of petals b – white color of petals P ♀ BB ♂ bb purple white gametes B b F 1 Bb pink x
Codominance I A - antigens A I B - antigens B type of interaction of allelic genes, in which both allelic genes are manifested in heterozygous organisms. i 0 – absence of antigens Genotype Antigens on the surface of erythrocytes Blood group i 0 i 0 0 (I) I A I A I A i 0 A (II) I B I B I B i 0 B (III) I A I B AB (IV) absence of antigens antigens A antigens B antigens A and B ( codominant)
(from lat. kompementum - addition) a type of interaction of non-allelic genes, in which the trait manifests itself only in the case of the simultaneous presence of two dominant non-allelic genes in the genotype of the organism. A and B - normal hearing other options - deafness deaf deaf gametes Ab aB Complementarity normal hearing (complementarity) P ♀ AAbb ♂ aaBB x F 1 AaBb
Epistasis (from the Greek epistasis - stop, obstacle) is a type of interaction of non-allelic genes, in which one gene suppresses the action of another non-allelic gene. S - suppresses I A and I B gr. blood 0 gr. blood B gametes i 0 S I B s I A - antigens A I B - antigens B i 0 - lack of antigens s - does not suppress I A and I B gr. blood 0 (epistasis) P ♀ i 0 i 0 SS ♂ I B I B ss x F 1 I B i 0 Ss
(from Greek poly - many) a type of interaction of non-allelic genes, in which the degree of manifestation of a trait depends on the number of dominant non-allelic genes in the genotype of the organism. A - dark skin color black woman white mulatto gametes AB ab a - light skin color B - dark skin color b - light skin color P ♀ AABB ♂ aabb x F 1 AaBb Polymeria
1 The integrity of the genotype is evidenced by the interaction of genes. How does it manifest itself?
The characteristics of any organism are determined by the proteins that make up the cells. Why is it believed that the formation of the characteristics of an organism occurs under the influence of genes? 2
What is the relationship between genes, proteins and traits of an organism? 3
The genotype cannot be viewed as the sum of genes. Explain why? 4
What does the interaction and multiple action of genes indicate? What are the differences between these phenomena? 5
The term "genotype" was proposed in 1909 by the Danish geneticist Wilhelm Johansen. He also introduced the terms: "gene", "allele", "phenotype", "line", "pure line", "population".
The genotype is the totality of the genes of an organism. A person has about 100 thousand genes.
The genotype as a single functional system of the body has developed in the process of evolution. A sign of the systemic nature of the genotype is the interaction of genes.
Allelic genes (more precisely, their products - proteins) can interact with each other:
In the composition of chromosomes - an example is the complete and incomplete linkage of genes;
In a pair of homologous chromosomes - examples are complete and incomplete dominance, codominance (independent manifestation of allelic genes).
Non-allelic genes interact in the following forms:
Cooperation - the appearance of neoplasms when two outwardly identical forms are crossed. For example, the inheritance of the crest shape in chickens is determined by two genes:
R - pink comb;
P - pea-shaped comb.
pink pea
F1 RrPp - the appearance of a walnut crest in the presence of two dominant genes; with the rrpp genotype, a leaf-shaped ridge appears;
Complementary interaction - the appearance of a new trait in the presence of two dominant non-allelic genes in the genotype. With such an interaction, four variants of splitting may appear in the second generation. An example is the development of anthocyanin (coloring pigment) in sweet pea flowers. If there is at least one recessive allele in the homozygous state, the color does not develop and the petals remain white:
Epistasis, or an interaction in which the gene of one allelic pair suppresses the action of the gene of another allelic pair. If two different dominant alleles are present in the genotype, then one of them appears during epistasis. The manifested gene is called the suppressor, the repressed gene is called hypostatic. When crossing two white chickens (leghorn Aabb and Wyandotte Aabb), in the second generation, phenotypic splitting will occur in relation to 13/16 whites - in cases where both are found in the genotype dominant gene, or in the case of a complete recessive genotype and 3/16 - colored - in cases where there is only one of the domi-
nant genes. In this case, gene A suppresses gene B. In the absence of gene A, gene B appears and the hens are colored;
Polymeria is the influence of several non-allelic genes of the same type on one trait. As a result, the degree of expression of a trait depends on the number of dominant alleles of different genes in the organism's genotype;
Pleiotropy - the influence of one gene on the development of several traits. In humans, a gene is known that causes the appearance of spider fingers (Marfan syndrome). At the same time, this gene causes a defect in the lens of the eye. The gene that causes red hair color affects skin pigmentation, the appearance of freckles.
The term "genotype" was proposed in 1909 by the Danish geneticist Wilhelm Johansen. He also introduced the terms: "gene", "allele", "phenotype", "line", "pure line", "population".
Genotype is the totality of the genes of an organism. A person has about 100 thousand genes.
The genotype as a single functional system of the body has developed in the process of evolution. A sign of the systemic nature of the genotype is the interaction of genes.
Allelic genes (more precisely, their products - proteins) can interact with each other:
- in the composition of chromosomes - an example is the complete and incomplete linkage of genes;
- in a pair of homologous chromosomes - examples are complete and incomplete dominance, codominance (independent manifestation of allelic genes).
Non-allelic genes interact in the following forms:
1.19. Variability, its types and biological significance
Variability- this is a universal property of living systems associated with variations in the phenotype and genotype that arise under the influence of the external environment or as a result of changes in hereditary material. Distinguish between hereditary and non-hereditary variability.
Hereditary variability is combinative, mutational, indefinite.
Combination variability arises as a result of new combinations of genes in the process of sexual reproduction, crossing over, and other processes accompanied by gene recombinations. As a result of combinative variability, organisms arise that differ from their parents in genotypes and phenotypes.
Mutational variability is associated with changes in the sequence of nucleotides in DNA molecules, deletions and insertions of large sections in DNA molecules, changes in the number of DNA molecules (chromosomes). Such changes are called mutations. Mutations are inherited.
Mutations are:
- genes that cause changes to a specific gene. Gene mutations are both dominant and recessive. They can support or, conversely, inhibit the vital activity of the organism;
- generative, affecting germ cells and transmitted during sexual reproduction;
- somatic, not affecting germ cells. In animals they are not inherited, but in plants they are inherited during vegetative propagation;
- genomic (polyploidy and heteroploidy) associated with a change in the number of chromosomes in the cell karyotype;
- chromosomal, associated with rearrangements in the structure of chromosomes, a change in the position of their sections resulting from breaks, loss of individual sections, etc.
The most common gene mutations, as a result of which there is a change, loss or insertion of DNA nucleotides in the gene. Mutant genes transmit different information to the site of protein synthesis, and this, in turn, leads to the synthesis of other proteins and the emergence of new traits. Mutations can occur under the influence of radiation, ultraviolet radiation, and various chemical agents. Not all mutations are effective. Some of them are corrected during DNA repair. Phenotypically, mutations are manifested if they did not lead to the death of the organism. Most gene mutations are recessive. Of evolutionary importance are phenotypically manifested mutations, either providing individuals with advantages in the struggle for existence, or, conversely, causing their death under the pressure of natural selection.
The mutation process increases the genetic diversity of populations, which creates the prerequisites for the evolutionary process.
The frequency of mutations can be increased artificially, which is used for scientific and practical purposes.
Non-hereditary variability
Non-hereditary, or group (certain), or modification variability are changes in the phenotype under the influence of environmental conditions. Modification variability does not affect the genotype of individuals. The limits in which the phenotype can change are determined by the genotype. These limits are called the reaction rate. The reaction norm sets the boundaries within which a particular feature can change. Various features have different norm reactions - wide or narrow. For example, the variability of the mammalian eye is small and has a narrow reaction rate. Milk yield of cows can vary over a fairly wide range depending on the conditions of the breed.
The phenotypic manifestations of a trait are influenced by the cumulative interaction of genes and environmental conditions. The degree of manifestation of a trait is called expressivity. The frequency of manifestation of a trait (%) in a population where all of its individuals carry this gene is called penetrance. Genes can manifest themselves with varying degrees of expressivity and penetrance. For example, a baldness gene can be expressed with a penetrance of 100% or 50%, depending on the specific environmental conditions, the number and interaction of the genes responsible for the development of the trait.
Modification changes are not inherited in most cases, but they do not necessarily have a group character and do not always appear in all individuals of a species under the same environmental conditions. Modifications ensure that the individual is adapted to these conditions.
