Match each statement (a–e) with the best answer from the follo...

Question

Match each statement (a–e) with the best answer from the following list: consultand, 50%, prior probability, 66.7%, obligate carrier, 100%.

The probability that the healthy brother of a woman with an autosomal recessive condition is a heterozygous carrier

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. It says a man has a brother suffering from cystic fibrosis, which is an autosomal recessive disorder. What is the probability that the man is a carrier? If neither of his parents have cystic fibrosis? And our answer choices are A zero B 1/4 C one half or D 3/4. So we want to think through what this man's genotype has the probability of being. So we know we're talking about an autism recessive disorder. So to have the disease, the genotype has to be little c little C we'll say that C is the gene for cystic fibrosis. And we're saying, what is the probability the man is a carrier if neither of his parents have cystic fibrosis, but his brother does. So, if neither parent has cystic fibrosis, we know they can't be homozygous recessive. The parents would have to be either homozygous dominant or heterozygous for the gene. However, since they have a child who is homozygous recessive, since their child is affected by the disease, the parents must be heterozygous, not homozygous dominant. Since their child who's affected must have inherited one alley for the disease from each of them. So with that in mind, we can look at the pundit square um for this particular family, for these parents to determine the probability that the man our problem is asking about is a carrier of the disease. So I've put up a four square puet square, since we're talking about just one gene here, and we know that both parents are heterozygous for the gene. So on the top, for one parent, we have Big C and Little Sea. And then on the left side, also big C and little C representing two heterozygous parents. So the probability of their offspring then in the top left box, we have homozygous dominant, big C big C, bottom, left, big C little C, top, right, big C, little C and bottom, right, little C little C. So we're looking for the probability that a man is a carrier given that these are his parents. Well, a carrier will be having one, all one copy of this all um because they do carry the gene but they're not affected by the disease. So that means they're a heterozygote. And as we see from our square, we had two out of four offspring predicted to be heterozygous, our lower left box and our upper right box. So that probability is going to equal 2/4 which will equal one half. And as we recall from our answer, choices, choice C is one half. So if a man has a brother suffering from cystic fibrosis which is autosomal recessive. What is the probability that the man is a carrier if neither of his parents have cystic fibrosis? And that's choice. C one half see you in the next video.

Match each statement (a–e) with the best answer from the following list: consultand, 50%, prior probability, 66.7%, obligate carrier, 100%.
The probability that the healthy brother of a woman with an autosomal recessive condition is a heterozygous carrier

Key Concepts

Autosomal Recessive Inheritance

Carrier Probability

Prior Probability

Watch next