Mendel's laws. Mendel's laws Splitting according to Mendel's 1st law

This article briefly and clearly describes Mendel's three laws. These laws are the basis of all genetics; by creating them, Mendel actually created this science.

Here you will find a definition of each law and learn a little something new about genetics and biology in general.

Before you start reading the article, you should understand that the genotype is the totality of the genes of an organism, and the phenotype is its external characteristics.

Who is Mendel and what did he do?

Gregor Johann Mendel is a famous Austrian biologist, born in 1822 in the village of Gincice. He studied well, but his family had financial difficulties. To deal with them, Johann Mendel in 1943 decided to become a monk at a Czech monastery in the city of Brno and received the name Gregor there.

Gregor Johann Mendel (1822 - 1884)

Later he studied biology at the University of Vienna, and then decided to teach physics and natural history in Brno. At the same time, the scientist became interested in botany. He conducted experiments on crossing peas. Based on the results of these experiments, the scientist derived three laws of heredity, which are the subject of this article.

Published in the work “Experiments with Plant Hybrids” in 1866, these laws did not receive wide publicity, and the work was soon forgotten. It was remembered only after Mendel’s death in 1884. You already know how many laws he derived. Now it's time to move on to looking at each.

Mendel's first law - the law of uniformity of first generation hybrids

Consider the experiment conducted by Mendel. He took two types of peas. These species were distinguished by the color of their flowers. One had them purple, and the other had them white.

Having crossed them, the scientist saw that all the offspring had purple flowers. And yellow and green peas produced completely yellow offspring. The biologist repeated the experiment many more times, checking the inheritance of different traits, but the result was always the same.

Based on these experiments, the scientist derived his first law, here is its formulation: all hybrids in the first generation always inherit only one trait from their parents.

Let us designate the gene responsible for purple flowers as A, and for white flowers as a. The genotype of one parent is AA (purple), and the second is aa (white). The A gene will be inherited from the first parent, and a from the second. This means that the genotype of the offspring will always be Aa. A gene designated by a capital letter is called dominant, and a lowercase letter is called recessive.

If the genotype of an organism contains two dominant or two recessive genes, then it is called homozygous, and an organism containing different genes is called heterozygous. If the organism is heterozygous, then the recessive gene, designated by a capital letter, is suppressed by a stronger dominant one, resulting in the manifestation of the trait for which the dominant one is responsible. This means that peas with genotype Aa will have purple flowers.

Crossing two heterozygous organisms with different characteristics is a monohybrid cross.

Codominance and incomplete dominance

It happens that a dominant gene cannot suppress a recessive one. And then both parental characteristics appear in the body.

This phenomenon can be observed in the example of camellia. If in the genotype of this plant one gene is responsible for red petals and the other for white, then half of the camellia petals will become red and the rest white.

This phenomenon is called codominance.

Incomplete dominance is a similar phenomenon, in which a third characteristic appears, something between what the parents had. For example, a night beauty flower with a genotype containing both white and red petals turns pink.

Mendel's second law - the law of segregation

So, we remember that when two homozygous organisms are crossed, all offspring will take on only one trait. But what if we take two heterozygous organisms from this offspring and cross them? Will the offspring be uniform?

Let's get back to peas. Each parent is equally likely to pass on either gene A or gene a. Then the offspring will be divided as follows:

• AA - purple flowers (25%);
• aa - white flowers (25%);
• Aa - purple flowers (50%).

It can be seen that there are three times more organisms with purple flowers. This is a splitting phenomenon. This is the second law of Gregor Mendel: when heterozygous organisms are crossed, the offspring are split in a ratio of 3:1 in phenotype and 1:2:1 in genotype.

However, there are so-called lethal genes. If they are present, a deviation from the second law occurs. For example, the offspring of yellow mice are split in a 2:1 ratio.

The same thing happens with platinum-colored foxes. The fact is that if in the genotype of these (and some other) organisms both genes are dominant, then they simply die. As a result, a dominant gene can only be expressed if the organism is heterozyotic.

The law of gamete purity and its cytological basis

Let's take yellow peas and green peas, the yellow gene is dominant, and the green gene is recessive. The hybrid will contain both of these genes (although we will only see the manifestation of the dominant one).

It is known that genes are transferred from parent to offspring using gametes. A gamete is a sex cell. There are two genes in the hybrid genotype; it turns out that each gamete - and there are two of them - contained one gene. Having merged, they formed a hybrid genotype.

If in the second generation a recessive trait characteristic of one of the parent organisms appeared, then the following conditions were met:

• the hereditary factors of the hybrids did not change;
• each gamete contained one gene.

The second point is the law of gamete purity. Of course, there are not two genes, there are more of them. There is a concept of allelic genes. They are responsible for the same sign. Knowing this concept, we can formulate the law as follows: one randomly selected gene from an allele penetrates into the gamete.

The cytological basis of this rule: cells in which there are chromosomes containing pairs of alleles with all the genetic information, divide and form cells in which there is only one allele - haploid cells. In this case, these are gametes.

Mendel's third law - the law of independent inheritance

The fulfillment of the third law is possible with dihybrid crossing, when not one trait is studied, but several. In the case of peas, this is, for example, the color and smoothness of the seeds.

We will denote the genes responsible for seed color as A (yellow) and a (green); for smoothness - B (smooth) and b (wrinkled). Let's try to carry out dihybrid crossing of organisms with different characteristics.

The first law is not violated during such crossing, that is, the hybrids will be identical in both genotype (AaBb) and phenotype (with yellow smooth seeds).

What will the split be like in the second generation? To find out, you need to find out what gametes the parent organisms can secrete. Obviously these are AB, Ab, aB and ab. After this, a circuit called a Pinnett lattice is constructed.

All the gametes that can be released by one organism are listed horizontally, and all the gametes that can be released by another are listed vertically. Inside the grid, the genotype of the organism that would appear with the given gametes is recorded.

If you study the table, you can come to the conclusion that the splitting of second-generation hybrids by phenotype occurs in the ratio 9:3:3:1. Mendel also realized this after conducting several experiments.

In addition, he also came to the conclusion that which of the genes of one allele (Aa) gets into the gamete does not depend on the other allele (Bb), that is, there is only independent inheritance of traits. This is his third law, called the law of independent inheritance.

Conclusion

Mendel's three laws are the basic genetic laws. Thanks to the fact that one person decided to experiment with peas, biology received a new section - genetics.

With its help, scientists from all over the world have learned many things, from disease prevention to genetic engineering. Genetics is one of the most interesting and promising branches of biology.

In the 50-60s of the 19th century, the Austrian biologist and monk Gregor Mendel conducted experiments on crossing peas. As a result of statistical processing of data, Mendel not only established, but was also able to explain a number of genetic patterns. This is despite the fact that at that time they knew nothing about DNA and genes as carriers of hereditary information. Gregor Mendel is considered the father of genetics.

Even before Mendel, a number of scientists at the beginning of the 19th century noted that hybrids of some plants exhibit the trait of only one parent. But only Mendel thought of studying the statistical relationships of hybrids over several generations. In addition, he was lucky with the choice of object for experiments - peas. Mendel studied seven traits of this plant, and almost all of them were inherited as being on different chromosomes and complete dominance was observed. If linked traits were found, as well as those inherited by the type of incomplete dominance or codominance, etc., this would introduce confusion into the scientist’s research.

The patterns of inheritance established by Mendel are now called Mendel's first, second and third laws. Mendel's first law is the law of uniformity of first generation hybrids.

Mendel carried out monohybrid crosses. He took pure lines that differed only in one alternative pair of characteristics. For example, plants with yellow and green seeds (or smooth and wrinkled, or high and low stems, or axillary and apical flowers, etc.) cross-pollinated pure lines and obtained first-generation hybrids. (The designation of generations F 1, F 2 was introduced at the beginning of the 20th century.) In all F 1 hybrids, the trait of only one of the parents was observed. Mendel called this trait dominant. In other words, all first generation hybrids were the same.

The second, recessive trait disappeared in the first generation. However, it manifested itself in the second generation. And this required some explanation.

Based on the results of two crosses (F 1 and F 2), Mendel realized that two factors are responsible for each trait in plants. In pure lines they were also paired, but identical in essence. First generation hybrids received one factor from each parent. These factors did not merge, but remained separate from each other, but only one could manifest itself (which turned out to be dominant).

Mendel's first law is not always formulated as the law of uniformity of first-generation hybrids. There is also a similar formulation: nThe signs of an organism are determined by pairs of factors,and ingametes by one factorfor every sign. (These “factors” of Mendel are now called genes.) Indeed, an important conclusion that could be drawn from Mendel’s experiments is that organisms contain two carriers of information about each trait, transmit one factor to their descendants through gametes, and In the body, the factors that cause the same symptom do not mix with each other.

Mendel's laws received a deeper genetic, as well as cytological and molecular explanation later. Exceptions to the laws were identified and explained.

Pure lines are homozygotes. They have the same pair of alleles under study (for example, AA or aa). Acting as the parent (P), one plant produces gametes containing only the A gene, and the other produces only the a gene. The first generation hybrids (F 1) obtained from their crossing are heterozygous, since they have the Aa genotype, which, with complete dominance, phenotypically manifests itself as the homozygous AA genotype. It is this pattern that Mendel's first law describes.

In the diagram below, w is the gene responsible for the white color of the flower, R is for the red color (this trait is dominant). Black lines indicate different options for meeting gametes. They are all equally likely. (Such a “drawing” of the meeting of gametes will be important in explaining Mendel’s second law.) In any case (at any meeting of parental gametes), the first generation hybrids form the same genotypes - Rw.

Having obtained uniform first-generation hybrids from crossing two different pure lines of peas, differing only in one trait, Mendel continued the experiment with F 1 seeds. He allowed the first generation pea hybrids to self-pollinate, resulting in second generation hybrids - F 2. It turned out that some of the plants of the second generation had a trait that was absent in F1, but present in one of the parents. Consequently, it was present in F 1 in a latent form. Mendel called this trait recessive.

Statistical analysis showed that the number of plants with a dominant trait is related to the number of plants with a recessive trait as 3:1.

Mendel's second law is called the law of segregation, since uniform hybrids of the first generation give different offspring (i.e., they seem to split).

Mendel's second law is explained as follows. First generation hybrids from crossing two pure lines are heterozygotes (Aa). They form two types of gametes: A and a. The following zygotes can be formed with equal probability: AA, Aa, aA, aa. Indeed, let’s say a plant produces 1000 eggs, 500 of which carry the A gene, 500 carry the a gene. 500 sperm A and 500 sperm a were also produced. According to probability theory approximately:

250 eggs A will be fertilized by 250 sperm A, 250 zygotes AA will be obtained;

250 eggs A will be fertilized by 250 sperm a, 250 zygotes Aa will be obtained;

250 eggs a will be fertilized by 250 sperm A, 250 zygotes aA will be obtained;

250 eggs a will be fertilized by 250 sperm a, resulting in 250 zygotes aa.

Since genotypes Aa and aA are the same thing, we get the following distribution of the second generation by genotype: 250AA: 500Aa: 250aa. After reduction we get the relation AA: 2Aa: aa, or 1: 2: 1.

Since, with complete dominance, genotypes AA and Aa appear phenotypically identically, then the phenotypic split will be 3:1. This is what Mendel observed: ¼ of the plants in the second generation turned out to have a recessive trait (for example, green seeds).

The diagram below (represented in the form of a Punnett grid) shows the crossing (or self-pollination) of first-generation hybrids (Bb), which were previously obtained by crossing pure lines with white (bb) and pink (BB) flowers. F 1 hybrids produce gametes B and b. Found in different combinations, they form three varieties of the F 2 genotype and two varieties of the F 2 phenotype.

Mendel's second law is a consequence law of gamete purity: only one allele of the parent gene enters the gamete. In other words, the gamete is pure from the other allele. Before the discovery and study of meiosis, this law was a hypothesis.

Mendel formulated the hypothesis of the purity of gametes, based on the results of his research, since the splitting of hybrids in the second generation could only be observed if the “hereditary factors” were preserved (although they might not appear), were not mixed, and each parent could transmit to each offspring only one (but any) of them.

Mendel's laws- principles of transmission of hereditary characteristics from parent organisms to their descendants, resulting from the experiments of Gregor Mendel. These principles formed the basis for classical genetics and were subsequently explained as a consequence of the molecular mechanisms of heredity. Although three laws are usually described in Russian-language textbooks, the “first law” was not discovered by Mendel. Of particular importance among the patterns discovered by Mendel is the “hypothesis of gamete purity.”

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Subtitles

Mendel's predecessors

At the beginning of the 19th century, J. Goss ( John Goss), experimenting with peas, showed that when crossing plants with greenish-blue peas and yellowish-white peas in the first generation, yellow-white ones were obtained. However, during the second generation, the traits that did not appear in the first generation hybrids and later called recessive by Mendel appeared again, and plants with them did not split during self-pollination.

Thus, by the middle of the 19th century, the phenomenon of dominance was discovered, the uniformity of hybrids in the first generation (all hybrids of the first generation are similar to each other), splitting and combinatorics of characters in the second generation. However, Mendel, highly appreciating the work of his predecessors, pointed out that they had not found a universal law for the formation and development of hybrids, and their experiments did not have sufficient reliability to determine numerical ratios. The discovery of such a reliable method and mathematical analysis of the results, which helped create the theory of heredity, is the main merit of Mendel.

Mendel's methods and progress of work

• Mendel studied how individual traits are inherited.
• Mendel chose from all the characteristics only alternative ones - those that had two clearly different options in his varieties (the seeds are either smooth or wrinkled; there are no intermediate options). Such a conscious narrowing of the research problem made it possible to clearly establish the general patterns of inheritance.
• Mendel planned and carried out a large-scale experiment. He received 34 varieties of peas from seed-growing companies, from which he selected 22 “pure” varieties (which do not produce segregation according to the studied characteristics during self-pollination). Then he carried out artificial hybridization of varieties, and crossed the resulting hybrids with each other. He studied the inheritance of seven traits, studying a total of about 20,000 second-generation hybrids. The experiment was facilitated by a successful choice of object: peas are normally self-pollinating, but it is easy to carry out artificial hybridization on them.
• Mendel was one of the first in biology to use precise quantitative methods to analyze data. Based on his knowledge of probability theory, he realized the need to analyze a large number of crosses to eliminate the role of random deviations.

Mendel called the manifestation of the trait of only one of the parents in hybrids as dominance.

Law of uniformity of first generation hybrids(Mendel’s first law) - when crossing two homozygous organisms belonging to different pure lines and differing from each other in one pair of alternative manifestations of the trait, the entire first generation of hybrids (F1) will be uniform and will carry the manifestation of the trait of one of the parents.

This law is also known as the "law of trait dominance." Its formulation is based on the concept clean line regarding the trait being studied - in modern language this means homozygosity of individuals for this trait. The concept of homozygosity was later introduced by W. Batson in 1902.

When crossing pure lines of purple-flowered peas and white-flowered peas, Mendel noticed that the descendants of the plants that emerged were all purple-flowered, with not a single white one among them. Mendel repeated the experiment more than once and used other signs. If he crossed peas with yellow and green seeds, all the offspring would have yellow seeds. If he crossed peas with smooth and wrinkled seeds, the offspring would have smooth seeds. The offspring from tall and short plants were tall.

Codominance and incomplete dominance

Some opposing characters are not in the relation of complete dominance (when one always suppresses the other in heterozygous individuals), but in the relation incomplete dominance. For example, when pure lines of snapdragons with purple and white flowers are crossed, the first generation individuals have pink flowers. When pure lines of black and white Andalusian chickens are crossed, gray chickens are born in the first generation. With incomplete dominance, heterozygotes have characteristics intermediate between those of recessive and dominant homozygotes.

The crossing of organisms of two pure lines, differing in the manifestations of one studied trait, for which the alleles of one gene are responsible, is called monohybrid crossing.

The phenomenon in which the crossing of heterozygous individuals leads to the formation of offspring, some of which carry a dominant trait, and some - a recessive one, is called segregation. Consequently, segregation is the distribution of dominant and recessive traits among the offspring in a certain numerical ratio. The recessive trait does not disappear in the first generation hybrids, but is only suppressed and appears in the second hybrid generation.

Explanation

Law of gamete purity- each gamete contains only one allele from a pair of alleles of a given gene of the parent individual.

Normally, the gamete is always pure from the second gene of the allelic pair. This fact, which could not be firmly established in Mendel's time, is also called the gamete purity hypothesis. This hypothesis was later confirmed by cytological observations. Of all the laws of inheritance established by Mendel, this “Law” is the most general in nature (it is fulfilled under the widest range of conditions).

Law of independent inheritance of characteristics

Definition

Law of independent inheritance(Mendel’s third law) - when crossing two individuals that differ from each other in two (or more) pairs of alternative traits, genes and their corresponding traits are inherited independently of each other and are combined in all possible combinations (as in monohybrid crossing).

When homozygous plants differing in several characters, such as white and purple flowers and yellow or green peas, were crossed, the inheritance of each character followed the first two laws, and in the offspring they were combined in such a way as if their inheritance had occurred independently of each other. The first generation after crossing had a dominant phenotype for all traits. In the second generation, a splitting of phenotypes was observed according to the formula 9:3:3:1, that is, 9:16 had purple flowers and yellow peas, 3:16 had white flowers and yellow peas, 3:16 had purple flowers and green peas, 1 :16 with white flowers and green peas.

Explanation

Mendel came across traits whose genes were located in different pairs of homologous chromosomes (nucleoprotein structures in the nucleus of a eukaryotic cell, in which most of the hereditary information is concentrated and which are intended for its storage, implementation and transmission) of the pea. During meiosis, homologous chromosomes of different pairs are randomly combined in gametes. If the paternal chromosome of the first pair gets into the gamete, then with equal probability both the paternal and maternal chromosomes of the second pair can get into this gamete. Therefore, traits whose genes are located in different pairs of homologous chromosomes are combined independently of each other. (It later turned out that of the seven pairs of characters studied by Mendel in the pea, which has a diploid number of chromosomes 2n = 14, the genes responsible for one of the pairs of characters were located on the same chromosome. However, Mendel did not discover a violation of the law of independent inheritance, since as linkage between these genes was not observed due to the large distance between them).

Basic provisions of Mendel's theory of heredity

In modern interpretation, these provisions are as follows:

• Discrete (separate, non-mixable) hereditary factors - genes (the term “gene” was proposed in 1909 by V. Johansen) are responsible for hereditary traits.
• Each diploid organism contains a pair of alleles of a given gene responsible for a given trait; one of them is received from the father, the other from the mother.
• Hereditary factors are transmitted to descendants through germ cells. When gametes are formed, each of them contains only one allele from each pair (the gametes are “pure” in the sense that they do not contain the second allele).

Conditions for the fulfillment of Mendel's laws

According to Mendel's laws, only monogenic traits are inherited. If more than one gene is responsible for a phenotypic trait (and the absolute majority of such traits), it has a more complex pattern of inheritance.

Conditions for fulfilling the law of segregation during monohybrid crossing

Splitting 3:1 by phenotype and 1:2:1 by genotype is performed approximately and only under the following conditions:

1. A large number of crosses (large number of offspring) are studied.
2. Gametes containing alleles A and a are formed in equal numbers (have equal viability).
3. There is no selective fertilization: gametes containing any allele fuse with each other with equal probability.
4. Zygotes (embryos) with different genotypes are equally viable.
5. The parent organisms belong to pure lines, that is, they are truly homozygous for the gene being studied (AA and aa).
6. The trait is truly monogenic

Conditions for the implementation of the law of independent inheritance

1. All conditions necessary for the fulfillment of the law of splitting.
2. The location of the genes responsible for the traits being studied is in different pairs of chromosomes (unlinked).

Conditions for fulfilling the law of gamete purity

1. The normal course of meiosis. As a result of chromosome nondisjunction, both homologous chromosomes from a pair can end up in one gamete. In this case, the gamete will carry a pair of alleles of all genes that are contained in a given pair of chromosomes.

Formulation 1 of Mendel's law The law of uniformity of the first generation of hybrids, or Mendel's first law. When crossing two homozygous organisms belonging to different pure lines and differing from each other in one pair of alternative traits, the entire first generation of hybrids (F1) will be uniform and will carry the trait of one of the parents

Formulation of the 2nd law of Mendel The law of segregation, or the second law of Mendel Mendel When two heterozygous descendants of the first generation are crossed with each other in the second generation, segregation is observed in a certain numerical ratio: by phenotype 3:1, by genotype 1:2:1.

Formulation 3 of Mendel's law Law of independent inheritance (Mendel's third law) When crossing two homozygous individuals that differ from each other in two (or more) pairs of alternative traits, genes and their corresponding traits are inherited independently of each other and are combined in all possible combinations (as and with monohybrid crossing). (The first generation after crossing had a dominant phenotype for all characteristics. In the second generation, a splitting of phenotypes was observed according to the formula 9: 3: 3: 1)

P AA BB aa bb x yellow, smooth seeds green, wrinkled seeds G (gametes) ABabab F1F1 Aa Bb yellow, smooth seeds 100% Mendel’s 3rd law DIHYBRID CROSSING. For the experiments, peas with smooth yellow seeds were taken as the mother plant, and peas with green wrinkled seeds were taken as the father plant. In the first plant both characters were dominant (AB), and in the second plant both were recessive (ab

The first generation after crossing had a dominant phenotype for all traits. (yellow and smooth peas) In the second generation, a splitting of phenotypes was observed according to the formula 9:3:3:1. 9/16 yellow smooth peas, 3/16 yellow wrinkled peas, 3/16 green smooth peas, 1/16 green wrinkled peas.

Task 1. In spaniels, black coat color dominates over coffee, and short hair dominates over long hair. The hunter bought a black dog with short hair and, to be sure that it was purebred, he carried out an analytical crossbreeding. 4 puppies were born: 2 short-haired black, 2 short-haired coffee. What is the genotype of the dog purchased by the hunter? Dihybrid crossing problems.

Problem 2. In a tomato, the red color of the fruit dominates over the yellow color, and the high stem dominates over the low stem. By crossing a variety with red fruits and a high stem and a variety with yellow fruits and a low stem, 28 hybrids were obtained in the second generation. The first generation hybrids were crossed with each other, resulting in 160 second generation hybrid plants. How many types of gametes does a first generation plant produce? How many plants in the first generation have red fruit and a tall stem? How many different genotypes are there among second-generation plants with red fruit color and tall stems? How many plants in the second generation have yellow fruit and a tall stem? How many plants in the second generation have yellow fruit and a low stem?

Task 3 In humans, brown eye color dominates over blue color, and the ability to use the left hand is recessive in relation to right-handedness. From the marriage of a blue-eyed, right-handed man with a brown-eyed, left-handed woman, a blue-eyed, left-handed child was born. How many types of gametes does the mother produce? How many types of gametes does the father produce? How many different genotypes can there be among children? How many different phenotypes can there be among children? What is the probability of having a blue-eyed, left-handed child in this family (%)?

Task 4 Crestedness in chickens dominates over the absence of a crest, and black plumage color dominates over brown. From crossing a heterozygous black hen without a crest with a heterozygous brown crested rooster, 48 chickens were obtained. How many types of gametes does a chicken produce? How many types of gametes does a rooster produce? How many different genotypes will there be among the chickens? How many tufted black chickens will there be? How many black chickens will there be without a crest?

Task 5 In cats, the short hair of the Siamese breed is dominant over the long hair of the Persian breed, and the black coat color of the Persian breed is dominant over the fawn color of the Siamese breed. Siamese cats crossed with Persian cats. When crossing hybrids with each other in the second generation, 24 kittens were obtained. How many types of gametes are produced in a Siamese cat? How many different genotypes were produced in the second generation? How many different phenotypes were produced in the second generation? How many second generation kittens look like Siamese cats? How many second generation kittens look like Persians?

Solving problems at home Option 1 1) A blue-eyed right-hander married a brown-eyed right-hander. They had two children - a brown-eyed left-hander and a blue-eyed right-hander. From this man’s second marriage to another brown-eyed, right-handed woman, 8 brown-eyed children were born, all right-handed. What are the genotypes of all three parents? 2) In humans, the gene for protruding ears dominates over the gene for normal flat ears, and the gene for non-red hair dominates over the gene for red hair. What kind of offspring can be expected from the marriage of a floppy-eared red-haired man, heterozygous for the first sign, with a heterozygous non-red-haired woman with normal flat-back ears. Option 2 1) In humans, clubfoot (R) dominates over the normal structure of the foot (R) and normal carbohydrate metabolism (O) over diabetes. A woman with a normal foot structure and normal metabolism married a club-footed man. From this marriage two children were born, one of whom developed clubfoot and the other diabetes mellitus. Determine the genotype of parents from the phenotype of their children. What phenotypes and genotypes of children are possible in this family? 2) In humans, the gene for brown eyes dominates over the gene for blue eyes, and the ability to use the right hand dominates left-handedness. Both pairs of genes are located on different chromosomes. What kind of children can they be if: the father is left-handed, but heterozygous for eye color, and the mother is blue-eyed, but heterozygous for the ability to use her hands.

Let's solve problems 1. In humans, normal carbohydrate metabolism dominates over the recessive gene responsible for the development of diabetes mellitus. The daughter of healthy parents is sick. Determine whether a healthy child can be born in this family and what is the probability of this event? 2. In people, brown eye color is dominant over blue. The ability to better use the right hand dominates over left-handedness; the genes for both traits are located on different chromosomes. A brown-eyed right-hander marries a blue-eyed left-hander. What kind of offspring should be expected in this pair?