Inheritance of eye color in humans: formation and patterns. Blue eyes are the result of a genetic mutation. The dominant eye color is blue or brown.
married a brown-eyed woman whose father had brown eyes and whose mother had blue eyes. What kind of offspring can be expected from this marriage?
In humans, the gene for brown eyes is dominant over the gene causing blue eyes. A blue-eyed man, one of the parents who had brown eyes, got marriedon a brown-eyed woman whose father had brown eyes and his mother had blue eyes. What kind of offspring can be expected from this marriage?
from crossing a cow and a bull,
heterozygous for coat color?
Problem No. 3. Guinea pigs have frizzy hair
wool is determined by a dominant gene, and
smooth - recessive.
1. Crossing two curled pigs between
produced 39 individuals with shaggy fur and
11 smooth-haired animals. How many among
individuals having a dominant phenotype,
must be homozygous for this
sign?
2. Guinea pig with shaggy fur
crossed with an individual with a smooth
wool, gave birth to 28 frizzy and 26
smooth-haired offspring. Define
genotypes of parents and offspring.
Task No. 4. An offspring was obtained at the fur farm
in 225 minks. Of these, 167 animals have
brown fur and 58 bluish-gray minks
coloring. Determine the genotypes of the original
forms, if it is known that the gene is brown
coloring dominates the gene,
defining bluish-gray color
wool
Problem No. 5. A person has a gene for brown eyes
dominates the gene causing
Blue eyes. Blue-eyed man, one
of whose parents had brown eyes,
married a brown-eyed woman who
the father had brown eyes, and the mother had blue eyes.
What kind of offspring can be expected from this
marriage?
Problem No. 6. Albinism is inherited in
human as a recessive trait. In family,
where one of the spouses is an albino, and the other has
pigmented hair, have two children.
One child is albino, the other is
dyed hair. What is the probability
birth of the next albino child?
Problems on di- and polyhybrid crossing
Problem No. 8. At a large cattle gene
polledness dominates the horned gene, and
gene for black coat color - above the gene
red color. Both pairs of genes are located
in different pairs of chromosomes.
1. What will the calves turn out to be like if they are crossed?
heterozygous for both pairs
signs of a bull and a cow?
2. What kind of offspring should be expected from
crossing a black polled bull,
heterozygous for both pairs of traits,
with a red horned cow?
Problem No. 9. Dogs have black fur
dominates the coffee, and the short coat
- over the long one. Both pairs of genes are in
different chromosomes.
1. What percentage of black shorthairs
puppies can be expected from crossing two
individuals heterozygous for both traits?
2. The hunter bought a black dog with a short
wool and wants to be sure that it is not
carries genes long hair coffee color.
Which partner according to phenotype and genotype do you need?
select for crossing to check
genotype of the purchased dog?
Problem No. 10. A person has a gene for brown eyes
dominates the gene that determines
development of blue eye color, and the gene
conditioning the ability to better master
right hand, predominates over the gene,
determining the development of left-handedness. Both
pairs of genes are located in different
chromosomes. What kind of children can they be if
Are their parents heterozygous?
3) One of the forms of glaucoma is determined by a dominant autosomal gene, and the second has an autosomal recessive type of inheritance. These genes are located on different pairs of chromosomes.
What is the probability of having a sick child if both parents are diheterozygous?
4) The gene for black color in cats is sex-linked. The other allele of this gene corresponds to the red color; heterozygous animals have a spotted ("tortoiseshell") coloration.
What will be the offspring from crossing a “tortoiseshell” cat with a ginger cat?
5) The forensic medical examination is tasked with finding out whether the boy in the family is his own or adopted. A blood test of the husband, wife and child showed: the wife is Rh-AB-IV blood type, the husband is Rh+O (I) blood type, the child is Rh-B (III) blood type.
What conclusion should the expert give and on what is it based?
6) When crossing a brown Great Dane with a white one, all the offspring are white. When breeding the resulting offspring "in themselves" we got 40 white, 11 black and 3 brown.
What type of gene interaction determines the inheritance of coat color in Great Danes? What is the genotype of the parents and offspring?
7) In chickens, striped color is due to the sex-linked dominant (B), and the absence of such striping is due to its recessive alleles (c). The presence of a crest on the head is a dominant autosomal gene (C), and its absence is a recessive allele (c). Two striped, combed birds were crossed and produced two chicks: a striped cockerel with a comb and a non-striped hen without a comb. Indicate the genotypes of the parental forms and offspring.
heard; but one has smooth hair and the other has curly hair, a deaf child was born with smooth hair. Their second child heard well and had curly hair.
What is the probability of having a deaf child with curly hair in such a family?
2) The gene for brown eyes is dominant over the gene for blue eyes. Brown-eyed man, whose parent had blue eyes, married a brown-eyed woman whose father had blue eyes and whose mother had brown eyes.
What kind of offspring can be expected from this marriage?
Right-handedness predominates over the left-handedness gene. What is the probability of having blue-eyed, left-handed children from the marriage of two diheterozygous parents?
in humans, the gene for brown eyes dominates the gene causing blue eyes, a blue-eyed man, one of whose parents has brown eyes, marriesa brown-eyed woman whose father has brown eyes and whose mother has blue eyes. What kind of offspring can be expected from this marriage.
1. A blue-eyed man, whose parents had brown eyes, married a brown-eyed woman, whose father had blue eyes and whose mother had blue eyes.brown. What kind of offspring can be expected from this marriage if it is known that the gene for brown eyes dominates the gene for blue eyes?
2. There were two brothers in the family. One of them is sick hemorrhagic diathesis, married a woman also suffering from this disease. All three of their children (2 girls and 1 boy) were also sick. The second brother was healthy and married healthy woman. Of their four children, only one was sick with hemorrhagic diathesis. Determine which gene determines hemorrhagic diathesis.
3. In a family where both parents had normal hearing, a deaf child was born. Which trait is dominant? What are the genotypes of all members of this family?
4. A man suffering from albinism marries a healthy woman whose father suffered from albinism. What kind of children can be expected from this marriage, given that albinism is inherited in humans as an autosomal recessive trait?
Many mothers, while expecting a baby, often think about how he will be born, what color eyes and hair he will have, what nose, lips and height he will have. Will he look like his parents or will he inherit the features of one of his relatives? Genetics can provide answers to these questions even before the baby is born.
Based on the laws of genetics, let's look at the algorithms by which a child's appearance is most often formed.
Eye color
If dad's eyes are dark brown, and mom's are blue, then the child has high probability There will be brown eyes. The gene for brown eyes is dominant (strong), and the gene for blue eyes is recessive (weak). If both parents have brown eyes, then they are unlikely to have a child with green, gray or blue eyes. Time will pass- and they will begin to darken, gradually turning into brown.
But if both parents are blue-eyed, then the baby will most likely have blue eyes.
Dominant traits
If at least one parent has dimples on the cheeks, a hooked (or large/crooked) nose, or protruding ears, then there is a very high probability that the child will also have this appearance feature. The fact is that these, as we generally believe, shortcomings are dominant signs and “peck out” in the baby’s appearance.
But, as a rule, only one such feature appears, less often - two at once.
Hair color
Gene dark hair outweighs the light gene because its pigment is strong. If both parents are fair, then the baby will also be born blonde or light brown. And if dad is a bright brunette, and mom is blonde, then the baby’s hair will be dark or light brown.
Interesting fact: a child who was born dark from this combination may have light-colored children in the future. The fact is that children of mixed genes receive both a strong gene from their father and a weak gene from their mother. Later, the weak gene can “merge” with the weak gene of the partner - and the child’s appearance will be light.
Also, the child may be completely different from you if he inherits wandering genes distant relatives. Thus, in a brown-haired family, a red-haired baby may suddenly be born, and there are also cases when a dark-skinned child was born to white-skinned parents, even if there were mulattoes in the family even several generations ago.
Source: instagram @sarahdriscollphoto
Curly or smooth hair
Wavy and curly hair is also a dominant trait that is most likely to appear in a child if at least one of the parents has it.
Blue and green, their inheritance results in two pairs of genes. The shades of these colors are determined individual characteristics The body distributes melanin in chromatophores, which are located in the iris. Other genes that are responsible for hair color and skin tone also affect the shade of eye color. For blond people with fair skin are typical, and representatives of the Negroid race have dark brown eyes.
The gene that is responsible only for eye color is located on chromosome 15 and is called HERC2, the second gene - EYCL 1 is located on chromosome 19. The first gene carries information regarding brown and blue color, the second is about green and blue.
The dominant color in the HERC2 allele is brown, in the EYCL 1 allele - green color, and blue eyes are inherited if there is a recessive trait in two genes. In genetics, it is customary to designate dominant capital letter Latin alphabet, the recessive trait is a lowercase letter. If a gene contains capital letters and lower case- the organism is heterozygous for this trait and has a dominant color, but a hidden recessive trait can be inherited by a child. A “suppressed” trait will appear in a baby when an absolute recessive allele is inherited from two parents. That is, parents may well have a blue-eyed child or with.
Using letters, brown eye color, which is determined by the HERC2 gene, can be designated AA or Aa, blue eyes correspond to the set aa. When a trait is inherited, the child receives one letter from each parent. Thus, if dad has a homozygous trait of brown eyes, and mom has blue eyes, then the calculations look like this: AA+aa=Aa, Aa, Aa, Aa, i.e. a child can only achieve the Aa set, which manifests itself according to the dominant, i.e. the eyes will be brown. But if the father is heterozygous and has the Aa set, and the mother is blue-eyed, the formula looks like: Aa+aa=Aa, Aa, aa,aa, i.e. there is a 50% chance that a child with a blue-eyed mother will have the same eyes. For blue-eyed parents, the eye inheritance formula looks like: aa+aa=aa,aa, aa, aa, in this case the baby inherits only the recessive allele aa, i.e. his eye color will be blue.
In the EYCL 1 allele, eye color is inherited in the same way as in the HERC2 gene, but only the letter A indicates green. Nature arranges it in such a way that the existing dominant trait of brown eyes in the HERC2 gene “defeats” the existing green trait in the EYCL 1 gene.
Thus, a child will always inherit brown eye color if one of the parents has a homozygous dominant set of AA in the HERC2 gene. If the parent brown eyes passes on the recessive gene a to the child, i.e. a sign of blue eyes, then the color of the eyes determines the presence of a green dominant trait in the EYCL 1 gene. In cases where a parent with green eyes does not transmit the dominant trait A, but “gives” the recessive allele a, the child is born with blue eyes.
Since eye color is determined by two genes, its shades are obtained from the presence of undetected characteristics. If a child has the AA genetic set in the HERC2 allele, then the eyes will be dark brown. Presence of the trait in the HERC2 gene brown eyes by type Aa, and in the EYCL 1 gene of the recessive trait aa, causes light brown eyes. Homozygous trait green eyes AA in the EYCL 1 locus determines a more saturated color than the heterozygous set Aa.
The color of the iris is formed by coloring pigments (melanocytes) and depends on their concentration in the stroma. If a small amount of coloring pigment is produced, the eyes will most likely be light (blue or gray). In people with brown and black eyes, melanocytes in the stroma are located in large quantities. The number of cells producing coloring pigment is determined at the level of genotype formation and is a hereditary factor.
Many newborns are born with a light blue iris. This happens due to the fact that the mechanism of melanin production has not yet been fully established. Around six months, the number of melanocytes increases and the baby's eyes may change color to a darker one. If a baby is born with brown eyes, the possibility that they will eventually become blue is zero, since brown is the predominant color, and blue is weaker (recessive).
Mechanisms of inheritance of eye color in humans
It is impossible to predict with absolute accuracy what color the baby’s iris will be. Mendel's laws say that iris color is inherited in the same way as hair color. Programming genes dark colors, are considered stronger (dominant), and the genes that create a light color are considered weaker. When forming a phenotype dominant gene takes over the recessive giving the eyes a stronger and more saturated color
Basic situations of gene interaction
Brown-eyed parent and blue-eyed parent (AA and aa)
The child of such a couple will have the genotype Aa, which means that the genotype of his brown-eyed father is AA, and his mother is aa. During the merger, the dominant genes interacted with the recessive ones and created the Aa pair, where the father's genes predominate. The probability that a child's eyes will be brown is 90%. There are exceptions, mostly girls, for some reason, fall under them, so the possibility of having a blue-eyed baby is also quite real, although only in 10% of general cases.
Brown-eyed parent (genotype Aa) and blue-eyed parent (aa)
In this situation, after the merger, the following four genotypes will appear: Aa, Aa, aa, aa. The chances of both genotypes are equal, since the probability of having a brown-eyed or blue-eyed child is the same (50 to 50).
Brown-eyed parents (genotype Aa)
In this case we see the formation of three pairs dominant genotype Ah, so in 75% of cases this couple will have a child with brown eyes.
Both parents with blue eyes (genotype aa)
In such a tandem, the probability of having a child with eyes like their parents is almost 100%, since the genotype of this couple absolutely does not contain the dominant gene “A”, which is responsible for dark color iris.
In relation to himself rare color eyes - green, blue will dominate, forming, so the probability of having a baby with green eyes will be 40%. If one parent has brown eyes and the other has green eyes, their child:
- in 50% of cases, be born with brown eyes;
- in 37% of cases with greens;
- and in 13% of cases will have blue eyes.
Recently, genetic scientists have identified 4 additional genes that affect the mechanism of inheritance of iris color. It was found that the genes of the ancestors, as well as their ancestors up to the 16th generation, are also responsible for the mechanism of formation of the color of the iris. Therefore, if parents with brown eyes give birth to a child with sky-colored eyes, this may be the result of a predominance of the grandparents' genes.
The mechanism of color inheritance is a rather complex genetic process, which is determined by the interaction of dominant and recessive genes. The formation of the number of melanocytes and their location as well as others hereditary factors and geographic location of a person.
