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
	bXd		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.

A question that many parents ask. However, it is impossible to answer this question unequivocally, since the answer depends 90% on genetic predisposition and 10% on chance.

Only one thing is clear here - the baby will be born with cloudy gray-blue or dark brown eyes.

What color will my child's eyes be?

Almost always, the eyes of newborns have a blue color, which subsequently, starting from 6 months, begins to change and darken as it is exposed to sunlight (although in most children this occurs between the ages of 6 months and a year). Around the age of three or four, the child’s eyes acquire their permanent color that remains for life.

Predicting a child's eye color

Below is a diagram that shows the “chances of success” of a particular eye color (in % ratio) depending on the eye color of the parents.

Also look at the site - determining the color of a child’s eyes by the color of the eyes of the baby’s parents and the color of the eyes of your parents. This is an English-language resource, but it won’t be difficult to figure out what’s what.

How reliable is this? Let's check it together! Please let us know in the comments whether the eye color in reality coincided with the predictions calculated and proposed using these methods.

Inheritance of eye color from a genetic point of view

The color of a child's eyes is determined by the parents' genes, but great-grandparents also contribute to the child's appearance. It turns out that their colors and shades have a polygenic inheritance pattern and are determined by the number and types of pigments in the iris cornea of ​​the eye.

In general, the color of a person’s eyes depends on the amount of melanin in the iris (melanin is also responsible for the color of our skin). In the spectrum of all possible variety of colors, one extreme point will be blue eye color (the amount of melanin is minimal), and the other is brown (the maximum amount of melanin). People with different eye colors fall somewhere between these extremes. And the gradation depends on the genetically determined amount of melanin in the iris.

Genetic studies show that the pigment component of the iris is controlled by 6 different genes. They interact with each other according to certain clear patterns, which ultimately leads to a wide variety of eye colors.

There is an established opinion that the color of a child’s eyes is inherited according to Mendel’s laws - eye color is inherited in almost the same way as hair color: genes for dark color are dominant, i.e. the distinctive features (phenotypes) encoded by them take precedence over the distinctive features encoded by the lighter color gene.

Parents with dark hair are more likely to have children with dark hair; the offspring of blond parents will be blond; and a child of parents whose hair color is different will have hair whose color will be somewhere in between the parents'.

However, the idea that brown-eyed parents can only have brown-eyed children is a fairly common misconception. A brown-eyed couple may well have a blue-eyed child, especially if one of the close relatives has a different eye color). The fact is that a person copies two versions of one gene: one from the mother, the other from the father. These two versions of the same gene are called alleles, with some alleles in each pair being dominant over the others. When it comes to genes that control eye color, brown will be dominant, however, a child can also receive a recessive allele from either parent.

Let us note some patterns in the inheritance of eye color by a child:

• Your husband and you have blue eyes - 99%, that the child will have exactly the same color or light gray. Only 1% gives the chance that your baby will have green eyes.
• If one of you has blue eyes and the other has green eyes, then the chances of the child having both eye colors are equal.
• If both parents have green eyes, then there is a 75% chance that the baby will have green eyes, a 24% chance of blue eyes, and a 1% chance of brown eyes.
• The combination of blue and brown eyes in parents gives a 50% to 50% chance for the child to have one or the other eye color.
• Brown and green parental eyes are 50% of children's brown eyes, 37.5% of green eyes and 12.5% ​​of blue eyes.
• Both parents have brown eyes. This combination will give the baby the same color in 75% of cases, green in 19%, and only in 6% babies can be blue-eyed.

Some fun facts about eye color

• The most common eye color around the world is brown.
• The rarest eye color is green - less than 2% of the total population of the Earth.
• Turkey has the highest percentage of citizens with green eyes, namely: 20%.
• For residents of the Caucasus, blue eye color is the most characteristic, not counting amber, brown, gray and green. Also, more than 80% of Icelandic residents have either blue or green eye color.
• There is such a phenomenon as heterochromia (from the Greek ἕτερος - “different”, “different”, χρῶμα - color) - different color of the iris of the right and left eyes or unequal coloring of different parts of the iris of one eyes.

Now you know what color your child’s eyes will be, and we, in turn, wish that, regardless of color, there is only happiness and joy in his beloved eyes!

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.

To answer the question The gene for brown eyes is considered dominant. Does he always win if the other parent's eyes are not brown? given by the author old-timer the best answer is 3:1, unless I forgot the arithmetic. That is, such parents will have three children with brown eyes, and the fourth with blue eyes. But if the brown-eyed person himself has grandparents with different eye colors, the likelihood that the child will be blue-eyed increases MAYBE....

Answer from Alina[guru]
No not always. Mom's eyes are brown, father's are blue. I have brown ones, my sister has blue ones, and my second sister has green ones. My son's father has brown eyes, that is, both parents have brown eyes, but his son's eye color is green.

Answer from Neurosis[guru]
no, in my opinion this is nonsense... if he doesn’t always win, why is he dominant?

Answer from Accomplice[newbie]
No, no and NO! My mom and dad are brown-eyed, and I have blue eyes! My husband has brown ones, and our children have blue ones! Here!

Answer from Alexey 11[guru]
Unfortunately it is so

Answer from Larisa Pavlova[guru]
no, not always, my eyes are gray and my husband’s are brown, our daughter’s eyes are gray like mine

Answer from EYES GREEN KNEES BLUE[guru]
In our case, the brown one won))) as you know, I have green eyes))

Answer from Diver[active]
not always but often

Answer from N.[guru]
We went through this at school, there are calculations on the power of probability, open the textbook “General Biology”.)

Answer from Yatyana[guru]
I have brown eyes, my husband has blue eyes, but my daughter still has blue eyes like her husband, which means that brown ones do not always dominate

Answer from Olka[newbie]
Not always!! ! A child does not necessarily inherit a dominant gene, but can also inherit a recessive one if it was present in previous generations). And we have brown-eyed parents and a blue-eyed daughter))

Answer from Anna Zilina[active]
won against us. My husband has brown eyes, my daughter also has brown eyes.

Answer from Kisa[expert]
Biology textbook for 9th grade. No not always.

Answer from ~Give me the Crown, Darling~[guru]
not always. my father is brown, and my mother is green

Answer from MarS[guru]
My wife and I have brown eyes, and my daughter has blue eyes, like her grandfather’s. AND.. . such a paradox. Until I was seven years old, my eyes were blue, and then they suddenly turned brown, that is, they became caried-dominated:.... (my father had blue eyes, my mother had brown eyes).

Answer from Irina I[guru]
Not always.

Answer from Hyperv strat[newbie]
We cannot isolate all alleles. Compared to all common alleles, it wins. But what if there is such a gray-brown-crimson color that its allele is more dominant? It's impossible to say for sure.

Answer from Vita[guru]
not always

Answer from Lyubov Semyonova[guru]
My eyes are green, my husband's are brown, and my daughter's are blue.

Answer from [email protected] [guru]
No. I have brown eyes, but our dad has blue eyes and our daughter has blue eyes.

Incredible facts

Researchers have proven that Blue eye color is the result of a genetic mutation that probably occurred between 6,000 and 10,000 years ago. Scientists say they have discovered the reason why some of us have blue pigment in the iris.

Professor Hans Eiberg, leader of the research team at the University of Copenhagen, claims that all humans originally had brown eyes. As a result of a genetic mutation, the color of the eyes has changed, and both of these pigments are present in the iris of the eyes of modern people.

According to experts, most likely blue eye color comes from the countries of the Middle East or the northern part of the Black Sea coast. It was in this area that the largest migration took place during the Neolithic period (about 6,000 - 10,000 years ago). People moved in huge groups to the northern part of Europe.

"These are just our guesses," says Professor Eyberg. According to him, this could also be the territory of the northern part of Afghanistan.

Genetic mutation

This mutation, which occurred thousands of years ago, affected the so-called OCA2 gene and literally, “turned off” the ability of brown eyes to produce dark pigment.

For those less educated on this issue, it is worth explaining that the OCA2 gene is involved in the production of melanin, the pigment that gives color to hair, eyes and skin. A mutation in neighboring genes does not completely immobilize the OCA2 gene, but it certainly limits its action, thereby reducing the production of melanin in the iris. Thus, brown eyes are “diluted” with blue pigment.

If the OCA2 gene were completely turned off, those who inherited this mutation would lose melanin for their skin, hair and iris. Sometimes this happens. We call people with a complete lack of melanin albinos.

Professor Eiberg and his colleagues examined the DNA of blue-eyed people from countries where the majority of the population has brown eyes. Residents of Jordan, India, Denmark and Turkey took part in a number of experimental observations.

The results of Professor Eyberg's research are very important for genetics in general. For the first time in 1996, a scientist suggested that the OCA2 gene is responsible for eye and hair color. From this moment, a very important stage began in the study of the OCA2 gene, as well as all processes in the body associated with this gene.

The results of this study were published in the journal Human Genetics, which clearly indicate that all blue-eyed inhabitants of our planet were once the owners of brown eyes, and only as a result of the mutation that occurred, the pigment of the eyes changed.

Albinism in humans

It is known that the cause of albinism is the absence of the enzyme tyrosinase, which is involved in the normal synthesis of melanin.

There are several main types of this genetic disorder:

1. Oculocutaneous albinism.

2. Temperature-sensitive albinism.

3. Ocular albinism.

Treatment of any of these types is unsuccessful. It is impossible to compensate for the lack of melanin or prevent various visual disorders that are an integral part of the disease.