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 are found in the stroma 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. Genes that program dark colors are considered stronger (dominant), and genes that create light colors are considered weaker. When forming a phenotype, the dominant gene takes precedence over the recessive one, 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, this 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 of the dominant genotype Aa, 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 giving birth to a child with eyes like those of the parents is almost 100%, since the genotype of this couple absolutely does not contain the dominant “A” gene, which is responsible for the dark color of the iris.

In relation to the rarest eye color - green, blue will dominate, forming, therefore 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 are also influenced by other hereditary factors and the geographic location of a person.

My friends know how much I am interested in the question of the color of my son's eyes.

For those who don’t know, I’ll tell you: Our dad has brown eyes. My eyes are green with pronounced heterochromia (there are brown veins in the eyes, the rim of the eyes is gray, the iris is green. That is, the eyes are three-colored).

Eye color: from grandparents to our grandchildren: how it is transmitted genetically.
Tables for calculating the eye color of an unborn child.

During pregnancy, many parents are eager to find out what eye color their unborn child will have. All answers and tables for calculating eye color are in this article.

Good news for those who want to pass on their exact eye color to their descendants: it is possible.

Recent research in the field of genetics has discovered new data on the genes that are responsible for eye color (previously 2 genes were known that were responsible for eye color, now there are 6). At the same time, today genetics does not have answers to all questions regarding eye color. However, there is a general theory that, even with the latest research, provides a genetic basis for eye color. Let's consider it.

So: every person has at least 2 genes that determine eye color: the HERC2 gene, which is located on human chromosome 15, and the gey gene (also called EYCL 1), which is located on chromosome 19.

Let's look at HERC2 first: humans have two copies of this gene, one from their mother and one from their father. HERC2 can be brown and blue, that is, one person has either 2 brown HERC2 or 2 blue HERC2 or one brown HERC2 and one blue HERC2:

HERC2 gene: 2 copies* Human eye color
Brown and Brown brown
Brown and blue brown
Blue and cyan blue or green

(*In all tables in this article, the dominant gene is written with a capital letter, and the recessive gene is written with a small letter, eye color is written with a small letter).

Where does the owner of two blue HERC2 green eyes come from - is explained below. In the meantime, here is some data from the general theory of genetics: brown HERC2 is dominant, and blue is recessive, so a carrier of one brown and one blue HERC2 will have brown eye color. However, a carrier of one brown and one blue HERC2 can pass on both brown and blue HERC2 to their children with a 50x50 probability, that is, the dominance of brown does not in any way affect the transmission of a copy of HERC2 to children.

For example, a wife has brown eyes, even if they are “hopelessly” brown: that is, she has 2 copies of brown HERC2: all children born with such a woman will be brown-eyed, even if the man has blue or green eyes, so how she will pass on one of her two brown genes to her children. But grandchildren can have eyes of any color:

So, for example:

HERC2 from the mother is brown (in the mother, for example, both HERC2 are brown)

HERC2 from father - blue (father, for example, has both HERC2 blue)

The child's HERC2 is one brown and one blue. The eye color of such a child is always brown; at the same time, he can pass on his blue HERC2 to his children (who can also receive blue HERC2 from the second parent and then have eyes either blue or green).

Now let's move on to the gey gene: it can be green and blue (blue, gray), each person also has two copies: a person receives one copy from his mother, the second from his father. Green gey is a dominant gene, blue gey is recessive. A person thus has either 2 blue gey genes or 2 green gey genes, or one blue and one green gey gene. At the same time, this affects the color of his eyes only if he has blue HERC2 from both parents (if he received brown HERC2 from at least one of his parents, his eyes will always be brown).

So, if a person received blue HERC2 from both parents, depending on the gey gene, his eyes may be the following colors:

Gey gene: 2 copies

Human eye color

Green and Green

Green

Green and blue

Green

blue and blue

Blue

General table for calculating the color of a child's eyes, brown eye color is indicated by “K”, green eye color is indicated by “Z” and blue eye color is indicated by “G”:

Eye color

Brown

Brown

Brown

Brown

Brown

Brown

Green

Green

Blue

Using this table, we can say with a high degree of probability that a child will have green eyes if both parents have green eyes or one parent has green eyes and the other has blue eyes. You can also say for sure that the child's eyes will be blue if both parents have blue eyes.

If at least one of the parents has brown eyes, their children may have brown, green or blue eyes.

Statistically:

With two brown-eyed parents, the probability that the child will have brown eyes is 75%, green - 18.75% and blue - 6.25%.

If one of the parents is brown-eyed and the other is green-eyed, the probability that the child will have brown eyes is 50%, green - 37.5%, blue - 12.5%.

If one of the parents is brown-eyed and the other is blue-eyed, the probability that the child will have brown eyes is 50%, blue - 50%, green - 0%.

Thus, if a child’s eyes are not the same color as his parents, there are genetic reasons and justifications for this, because “nothing disappears without a trace and nothing comes out of nowhere.”

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 has dark brown eyes and mom has blue eyes, then the child is likely to have 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. As time passes, they will begin to darken, gradually turning 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

The gene for dark hair outweighs the gene for light hair 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 from 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.

Eye color: how it is passed on from parents to child. Calculate the child's eye color.

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Eye color: from grandparents to our grandchildren: how it is transmitted genetically.
Tables for calculating the eye color of an unborn child.

During pregnancy, many parents are eager to find out what eye color their unborn child will have. All answers and tables for calculating eye color are in this article.

Good news for those who want to pass on their exact eye color to their descendants: it is possible.

Recent research in the field of genetics has discovered new data on the genes that are responsible for eye color (previously 2 genes were known that were responsible for eye color, now there are 6). At the same time, today genetics does not have answers to all questions regarding eye color. However, there is a general theory that, even with the latest research, provides a genetic basis for eye color. Let's consider it.

So: every person has at least 2 genes that determine eye color: the HERC2 gene, which is located on human chromosome 15, and the gey gene (also called EYCL 1), which is located on chromosome 19.

Let's look at HERC2 first: humans have two copies of this gene, one from their mother and one from their father. HERC2 can be brown and blue, that is, one person has either 2 brown HERC2 or 2 blue HERC2 or one brown HERC2 and one blue HERC2:

(*In all tables in this article, the dominant gene is written with a capital letter, and the recessive gene is written with a small letter, eye color is written with a small letter).

Where does the owner of two blue ones come from? HERC2 green eye color - explained below. In the meantime, some data from the general theory of genetics: brown HERC2 - dominant, and blue is recessive, so the carrier has one brown and one blue HERC2 eye color will be brown. However, to his children the bearer of one brown and one blue HERC2 with a 50x50 probability it can transmit both brown and blue HERC2 , that is, the dominance of brown has no effect on the transfer of the copy HERC2 children.

For example, a wife has brown eyes, even if they are “hopelessly” brown: that is, she has 2 copies of brown HERC2 : All children born to such a woman will be brown-eyed, even if the man has blue or green eyes, since she will pass on one of her two brown genes to the children. But grandchildren can have eyes of any color:

So, for example:

HERC2 about the mother's t is brown (the mother, for example, has both HERC2 brown)

HERC2 from the father - blue (father, for example, has both HERC2 blue)

HERC2 The child has one brown and one blue. The eye color of such a child is always brown; at the same time your HERC2 he can pass on the blue color to his children (who can also receive it from the second parent HERC2 blue and then have eyes either blue or green).

Now let's move on to the gene gay: it comes in green and blue (blue, grey); each person also has two copies: a person receives one copy from his mother, the second from his father. Green gay is the dominant gene, blue gay - recessive. A person thus has either 2 blue genes gay or 2 green genes gay or one blue and one green gene gay . At the same time, this affects the color of his eyes only if he has HERC2 from both parents - blue (if he received brown from at least one of the parents HERC2 , his eyes will always be brown).

So, if a person received blue from both parents HERC2 , depending on the gene gay his eyes can be the following colors:

gay gene: 2 copies	Human eye color
Green and Green	green
Green and blue	green
blue and blue	blue

General table for calculating a child's eye color, brown eye color is designated "K", green eye color is designated "Z" and blue eye color is designated "G":

HERC2	Gey	eye color
QC	ZZ	brown
QC	Zg	brown
QC	GG	brown
Kg	ZZ	brown
Kg	Zg	brown
Kg	GG	brown
yy	ZZ	green
yy	Zg	green
yy	GG

In humans, the gene for normal hearing (B) dominates over the gene for deafness and is located in the autosome; the gene for color blindness (color blindness - d) is recessive and linked to the X chromosome. In a family where the mother suffered from deafness but had normal color vision, and the father had normal hearing (homozygous) and was color blind, a color blind girl with normal hearing was born. Make a diagram for solving the problem. Determine the genotypes of the parents, daughters, possible genotypes of the children and the likelihood of the future birth of color-blind children with normal hearing and deaf children in this school.

Answer

B – normal hearing, b – deafness.

The mother is deaf, but has normal color vision bbX D X _ .
Father with normal hearing (homozygous), color blind BBX d Y.

The colorblind girl X d X d received one X d from her father and the second from her mother, therefore the mother is bbX D X d .

P	bbX D X d	x	BBX d Y
G	bX D		BX d
	bX d		BY
F1	BbX D X d		BbX D Y	BbX d X d	BbX d Y
	girls from normal hearing and vision		boys from normal hearing and vision	girls from normal hearing, colorblind	boys from normal hearing, colorblind

Daughter BbX d X d . Probability of having colorblind children = 2/4 (50%). All of them will have normal hearing, the probability of being born deaf = 0%.

In humans, the gene for brown eyes dominates over blue eyes (A), and the gene for color blindness is recessive (color blindness - d) and linked to the X chromosome. A brown-eyed woman with normal vision, whose father had blue eyes and suffered from color blindness, marries a blue-eyed man with normal vision. Make a diagram for solving the problem. Determine the genotypes of the parents and possible offspring, the likelihood of having color-blind children with brown eyes and their gender in this family.

Answer

A – brown eyes, and – blue eyes.
X D – normal vision, X d – color blindness.

Brown-eyed woman with normal vision A_X D X _ .
The woman's father is aaX d Y, he could only give his daughter aX d, therefore, the brown-eyed woman is AaX D X d.
The woman's husband is aaX D Y.

P AaX D X d x aaX D Y

The probability of having a colorblind child with brown eyes is 1/8 (12.5%) and it is a boy.

One form of anemia (blood disease) is inherited as an autosomal dominant trait. In homozygotes this disease leads to death, in heterozygotes it manifests itself in a mild form. A woman with normal vision, but a mild form of anemia, gave birth to two sons from a healthy (by blood) color-blind man - the first, suffering from a mild form of anemia and color blindness, and the second, completely healthy. Determine the genotypes of the parents, sick and healthy sons. What is the probability of having the next son without anomalies?

Answer

AA – death, Aa – anemia, aa – normal.
X D – normal vision, X d – color blindness.

A woman with normal vision but mild anemia AaX D X _ .
A healthy blood color-blind man aaX d Y.
The first child is AaX d Y, the second child is aaX D Y.

The first child received Y from his father, therefore, he received X d from his mother, therefore, his mother AaX D X d.

P AaX D X d x aaX d Y

The probability of having the next son without anomalies is 1/8 (12.5%).

Deafness is an autosomal trait; color blindness is a gender-linked trait. In the marriage of healthy parents, a child was born who was deaf and color blind. Make a diagram for solving the problem. Determine the genotypes of the parents and the child, its gender, genotypes and phenotypes of possible offspring, the likelihood of having children with both anomalies. What laws of heredity are manifested in this case? Justify your answer.

Answer

Healthy parents gave birth to a sick child, therefore, deafness and color blindness are recessive traits.

A - normal. hearing, a - deafness
X D - normal. vision, X d - color blindness.

The child has aa, the parents are healthy, therefore they are Aa.
The father is healthy, therefore he is X D Y. If the child were a girl, then she would have received X D from her father and would not be color blind. Consequently, the child is a boy and received the color blindness gene from his mother. The mother is healthy, therefore fire X D X d .

P AaX D X d x AaX D Y

	AX D	AY	aX D	aY
AX D	AAX D X D normal hearing normal vision girl	AAX D Y normal hearing normal vision boy	AaX D X D normal hearing normal vision girl	AaX D Y normal hearing normal vision boy
AX d	AAX d X D normal hearing normal vision girl	AAX d Y normal hearing colorblind boy	AaX d X D normal hearing normal vision girl	AaX d Y normal hearing colorblind boy
aX D	AaX D X D normal hearing normal vision girl	AaX D Y normal hearing normal vision boy	aaX D X D deafness normal vision girl	aaX D Y deafness normal vision boy
aX d	AaX d X D normal hearing normal vision girl	AaX d Y normal hearing colorblind boy	aaX d X D deafness normal vision girl	aaX d Y deafness color blindness boy

The probability of having a child with two anomalies is 1/16 (6.25%).

In this case, Medel's third law (the law of independent inheritance) appeared.

The shape of the wings in Drosophila is an autosomal gene, the gene for eye color is located on the X chromosome. The male sex is heterogametic in Drosophila. When female fruit flies with normal wings and red eyes were crossed and males with reduced wings and white eyes, all offspring had normal wings and red eyes. The resulting F1 males were crossed with the original parent female. Make a diagram for solving the problem. Determine the genotypes and phenotypes of parents and offspring in two crosses. What laws of heredity appear in two crosses?

Answer

In the first generation, uniform offspring were obtained (Mendel's first law), therefore the parents were homozygotes, F1 were heterozygotes, and heterozygotes showed dominant genes.

A - normal wings, a - reduced wings
B - red eyes, b - white eyes

P AAX B X B x aaX b Y
F1 AaX B X b , AaX B Y

AaX B Y x AAX B X B

	AX B	aX B	AY	aY
AX B	AAX B X B	AaX B X B	AAX B Y	AaX B Y

All offspring turned out to have normal wings and red eyes. In the second crossing, Mendel's third law (the law of independent inheritance) appeared.

In Drosophila, the heterogametic sex is male. Drosophila females with a gray body, red eyes and males with a black body, white eyes were crossed, all the offspring were uniform in body and eye color. In the second crossing of Drosophila females with a black body, white eyes and males with a gray body, red eyes, the offspring were females with a gray body, red eyes and males with a gray body, white eyes. Draw up crossing schemes, determine the genotypes and phenotypes of the parents, offspring in two crosses and the sex of the offspring in the first cross. Explain why the characteristics split in the second crossing.

Answer

A - gray body, a - black body
X E - red eyes, X E - white eyes

Since in the first crossing all the offspring were uniform, therefore, homozygotes were crossed:
P AA X E X E x aaX e Y
F1 AaX E X e, AaX E Y (all with gray body and red eyes)

Second crossing:
P aa X e X e x AAX E Y
F1 AaX e X E, AaX e Y (females with a gray body and red eyes, males with a gray body and white eyes)

The splitting of characters in the second generation occurred because the eye color trait is linked to the X chromosome, and males receive the X chromosome only from the mother.

In humans, the inheritance of albinism is not sex-linked (A - the presence of melanin in skin cells, and - the absence of melanin in skin cells - albinism), and hemophilia is sex-linked (X H - normal blood clotting, X h - hemophilia). Determine the genotypes of the parents, as well as the possible genotypes, sex and phenotypes of children from the marriage of a dihomozygous woman, normal for both alleles, and an albino man with hemophilia. Make a diagram for solving the problem.

Answer

A is normal, a is albinism.
X H - normal, X h - hemophilia.

Woman ААХ Н Х Н, man ааХ Н Х h.

Wing shape in Drosophila is an autosomal gene; the gene for eye size is located on the X chromosome. The male sex is heterogametic in Drosophila. When two fruit flies with normal wings and normal eyes were crossed, the offspring produced a male with curled wings and small eyes. This male was crossed with the parent. Make a diagram for solving the problem. Determine the genotypes of the parents and the resulting F1 male, and the genotypes and phenotypes of the F2 offspring. What proportion of females from the total number of offspring in the second cross is phenotypically similar to the parent female? Determine their genotypes.

Answer

Since crossing two fruit flies with normal wings resulted in a child with curled wings, therefore A - normal wings, a - curled wings, parents Aa x Aa, child aa.

The gene for eye size is linked to the X chromosome, therefore, a male with small eyes received Y from his father, and the gene for small eyes from his mother, but the mother herself had normal eyes, therefore, she was a heterozygote. X B - normal eyes, X b - small eyes, mother X B X b, father X B Y, child X b Y.

F1 AaX B X b x aaX b Y

Phenotypically similar to the parent female will be F2 AaX B X b, their 1/8 (12.5%) of the total number of offspring.