Skip navigation

3.5.1.3. Eye color (problems solved)

Autosomal dominant inheritance. Eye color (Page 4)

The color of the eyes is somewhat more complicated than what we are going to see here. It is not only determined by a single gene, but two are involved. The chromosome 15 with alleles M and m, where the presence, at the least, a M determines that the eyes are brown and the presence of the two eyes mm determines that are clear, blue or green. We, in the simulation, will stay here.

As we say, this type of inheritance is complicated because the other gene, on chromosome 19, will determine in people with light eyes (mm) whether the eyes will be  blue or green . Individuals who already have M in the first gene will have brown eyes regardless of the combination in the second gene. Therefore, this second gene only influences the phenotype in individuals of genotype mm. It has two alleles, V and v, the green eye color being dominant. Thus, if we have at least one V ( VV or Vv ) in this gene, the eye color will be green, and if we have both vv alleles, the eye color will be blue..

As we have said, in the simulation we will see what the eyes of the descendants (brown or light) look like depending on the genotype of the parents.

Genetics problem 19

In humans, the brown color of the eyes (A) is dominant over the blue color (a). A brown-eyed man and a blue-eyed woman have two children, one with brown eyes and the other with blue eyes. Find out all the genotypes:

Genetics problem 20

The blue color of the eyes in men is due to a recessive gene with respect to its allele for the color brown. The parents of a blue-eyed male both have brown eyes. What are their genotypes?

Genetics problem 21

a) Olga and Juan, both with brown eyes, have a male child (Luis) with blue eyes. What type of inheritance occurs? Indicate the genotype of the three individuals.

b) Luis, the son of Olga and Juan, married María, with brown eyes, whose mother (Pilar) was blue-eyed and whose father was brown-eyed. Maria had a brother with blue eyes. Luis and María had a son (Álvaro), with brown eyes. Indicate the genotypes of all the characters in this question.

Genetics problem 22

In the human species the color of the eyes is determined by a pair of alleles. A blue-eyed man marries a brown-eyed woman. The woman's mother was blue-eyed and the father, who had a blue-eyed brother, was brown-eyed. From the marriage a son with brown eyes was born. Indicates the probability of having a child with blue eyes. The color of brown eyes dominates over that of blue eyes.

Genetics problem 23

In the human species, the color of the eyes is an autosomal character where the allele of the brown color "A" dominates over that of the blue color "a". A brown-eyed man, whose mother has blue eyes, has two descendants with a blue-eyed woman. What are the genotypes of men and women? And those of the descendants? What is the probability that this couple has descendants with blue eyes? And the probability of having descendants with brown eyes? Reason for the answers.

Genetics problem 24

In the human species, black eyes dominate over blue eyes. A black-eyed man is joined by a  blue-eyed woman and they have a blue-eyed son.

  1. What are the genotypes of the black-eyed man, the blue-eyed woman, and the blue-eyed son?
    Give reasons for the answer.
  2. Can this couple have a child with black eyes? Give reasons for the answer.

Genetics problem 25

We assume that eye color in humans is controlled by a gene with two alleles: -b- responsible for blue eyes and -B, which produces brown eyes and is dominant over -b-:

a) What is the genotype of a brown-eyed man who has a blue-eyed son with a blue-eyed woman? Reason for the answer;

b) Considering the same previous mating, what proportion of the two eye colors would be expected in the offspring?;

c) What proportion would be expected in terms of eye color in the progeny of a mating between two brown-eyed individuals, each of which had a parent with blue eyes? Represents mating;

d) Which of Mendel's laws is supposed to apply in the proposed crossing in the question? Reason for the answer.