Percentage phenotype in eye color in humans

In humans, brown eyes are dominant to blue eyes. If a blue-eyed man marries a brown-eyed woman whose mother has blue eyes, what percentage of the brown-eyed offspring do you expect will be heterozygous?

so the man would be bb and the woman would be Bb, the kids would be Bb,bb,Bb,bb so the answer should be 50% but the webpage says that that's incorrect.

I agree with you. Possibly that is a typo on the web page.

To determine the percentage of brown-eyed offspring that are heterozygous in this scenario, we need to understand the principles of Mendelian genetics and eye color inheritance.

First, let's assign symbols to represent the alleles responsible for eye color. We'll use "B" to represent the dominant brown eye allele and "b" for the recessive blue eye allele. Since brown eyes are dominant, individuals with either BB (homozygous dominant) or Bb (heterozygous) genotypes will have brown eyes, while individuals with the bb (homozygous recessive) genotype will have blue eyes.

Now let's examine the given scenario. The blue-eyed man has the genotype bb, as blue eyes are always represented by the recessive allele bb. The brown-eyed woman has at least one dominant allele for brown eyes, so her genotype could be either BB or Bb.

Since the woman's mother has blue eyes, this implies that she inherited a recessive allele for blue eyes from her mother. This means the woman's genotype must be Bb. Therefore, the possible genotypes for the woman are BB and Bb (we can eliminate bb as she has brown eyes).

Now, let's consider the possible genotypes of the offspring. When two individuals with genotypes Bb (the woman) and bb (the man) have children, they can produce offspring with the following genotypes:

- Bb (25% probability): This represents a heterozygous individual with the potential to pass on either the dominant brown allele (B) or the recessive blue allele (b).
- bb (25% probability): This represents a homozygous recessive individual with blue eyes.
- Since the man is bb, there is no chance of getting a BB genotype, so no homozygous dominant individuals.

Therefore, in this scenario, there is a 25% chance that the brown-eyed offspring will be heterozygous (Bb).

To summarize, you can expect that approximately 25% of the brown-eyed offspring from a blue-eyed man and a brown-eyed woman whose mother has blue eyes will be heterozygous for eye color (Bb).