Question

Brown eyes in humans are dominant to blue eyes. A brown-eyed man, whose mother was blue-eyed, marries a brown-eyed woman whose father had blue eyes. What is the probability that this couple will have a blue-eyed child?

Answer 1

about a 50:50 chance

Answer 2

How?

Answer 3

well if the father had blue eyes then had a daughter with brown eyes that would mean that her mother had brown eyes so mixing brown eyes with blue eyes would result with a child of either brown or blue eyes. Yet there is a slight chance of a child with bluish-brown eyes. Therefore you have a 50:50 chance

Answer 4

facts

Answer 5

Let B = brown eyes and b = blue eyes. Just make a punnett square of both generations. Also, this is an autosomal trait so the sex will not matter.

For the brown-eyed man, the mother was blue eyes. That means the mother was bb, and there is no chance the brown-eyed man is homozygous dominant. He is likely to receive a recessive allele from his mom, and in order to be brown eyed, received a dominant allele from his father.

Now this man marries a brown-eyed woman whose father had blue eyes. Same principle here, the father of this woman was homozygous recessive or bb. As a result, the mother obtained the dominant phenotype via heterozygous inheritance, or Bb.

In short, both the husband and wife are Bb, or heterozygous.

The product of the combinations of two heterozygous inheritances, or Bb x Bb is always in the genotypic ratio of 1:2:1, and phenotypic ratio of 3:1. Thereafter, the probability the child of the next generation is blue eyed is the probability of getting a homozygous recessive, which is only 25%.

Answer 6

\(\color{#0cbb34}{\text{Originally Posted by}}\) @katkit25
well if the father had blue eyes then had a daughter with brown eyes that would mean that her mother had brown eyes so mixing brown eyes with blue eyes would result with a child of either brown or blue eyes. Yet there is a slight chance of a child with bluish-brown eyes. Therefore you have a 50:50 chance
\(\color{#0cbb34}{\text{End of Quote}}\)


By bluish brown eyes do you mean an incomplete inheritance? That's only possible if they mention it in the question, you cannot simply assume incomplete inheritance.

Answer 7

Even on the basis of your assumption, blue-eyed strictly means blue eyes. No incomplete or codominance. So it is still 25%

Answer 8

i was not assuming things it was just something to put out there bc one of my friends has one blue eye and one brown eye.

Answer 9

I see. well in fact, that is not exactly incomplete or codominance. The pigmentation of eye color is a pleiotropy. So that is definitely not applicable in the study of one gene.