The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.
What is the probability that female I-3 is a heterozygous carrier of the allele for albinism?

Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

Pedigree chart illustrating the inheritance of albinism in a family, highlighting individual I-3's potential carrier status.

What is the probability that female I-3 is a heterozygous carrier of the allele for albinism?

Accepted Answer

Hi, everyone. Let's look at our next question. If the mother is affected by an XLI dominant disorder, heterozygous, how will it affect their offspring? Well, to think this through, let's go ahead and draw a little punt square to predict the offspring. Since I'm talking about inheritance of the sex chromosomes, I just need a four square and it square. So I'll put that up here and across the top. I'm going to put the mother's chromosomes. So XX for the two sex chromosomes, we know the mother is heterozygous for an X link dominant disorder. So I'm just gonna call the allele for the disorder A for affected. So she's got one unaffected alley. I'll just leave that as plain X and the second X has a little superscript A to show that that is an affected allele for this disorder. The father is not affected. So down on the left side will be X just in a plain X unaffected X and Y. So we'll draw out the offspring recalling that this is a dominant disorder, meaning that being heterozygous for the disorder will cause the offspring to be affected. They don't need two copies as you would with the recessive disorder. So as I fill in my boxes, I've got an XX female in the top left who's inherited a normal from the mother, then we have normal XY down below. Then top, right. We've got another female XX superscript A because that females affected the inherited the affected allele from the mother and then bottom. Right, we have xay. So a male who's inherited the affected X chromosome from the mother. So we have two offspring out of four that are affected because they've inherited that copy of the defective exhale from their mother. The other two offspring inherited the normal ex all are, are unaffected. So we see, we see here, there's no gender difference. In this case when the mother is heterozygous. Um there obviously would be uh if the trait were carried by the father because the father only passes an X chromosome to female offspring. But in this case, it's one copy carried by the mother. And therefore you, since you only need to inherit one copy, it doesn't matter that the females have two XS and the males just have one since they only need to inherit one copy. So our answer choice is choice. B 50% of the offspring will get affected. See you in the next video.

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

What is the probability that female I-3 is a heterozygous carrier of the allele for albinism?

Verified video answer for a similar problem:

Key Concepts

Pedigree Analysis

Autosomal Recessive Inheritance

Genotype Probability Calculation