A 40-year-old woman whose father had Huntington disease curren...

Question

A 40-year-old woman whose father had Huntington disease currently shows no symptoms of the disease. She is newly pregnant with her first child and seeks your best estimate of the chance her child will inherit the disease. What is your estimate and how did you arrive at it? (Hint: See Figure 4.11)

Accepted Answer

Hello, everyone and welcome to today's video. So sco cell anemia is an auto recessive disorder. This means that in order to express sco cell anemia, we need both recessive all to be present in the genotype. Now, suppose we use a in lower case to denote the recessive allele associated with this condition. So which of the following process can produce offspring in which 50% are affected by this condition. Now, all we have to do is go over each of our answer choices and determine which one is going to yield a 50% probability of obtaining these homozygous recessive genotype. For answer choice A, we have homozygous dominant A and heterozygous A for answer choice. B, we have heterozygous A and heterozygous A for answer choice C, we have heterozygous A and homozygote recessive A. And as answer choice D we have homozygous recessive A and homozygous recessive A. Well, in order to solve this problem, like we said, we need to perform this process. And so we're going to be using these four, 2 x 2 punnet squares that we just inserted into the page in order to perform this process. So let's begin by A which is going to be homozygous A and heterozygous A and the cross is going to look like this. So as we can see, there is a 0% probability of obtaining the homo cys recessive phenotype. So we're going to cancel this out. Then let's look at B which is going to be Zaga A on top and he A on the bottom and perform these cross on the screen. As we can see, there is a 25% or 1/4 chance of obtaining the homo cycles, recessive phenotype. This is not going to be our answer. So we're going to cancel this out. Then let's look at D which is going to be homozygous, recessive A and homo cycles recessive A. So we're going to put one on top and one on the side and perform these cross as well as we can see, we're going to have a 100% chance of obtaining this S cell anemia genotype because of this. It is also going to be incorrect. Finally, let's look at C which is going to be heteros A being crossed with homozygosis A and that's what we're going to put at the top and on the sides. If we perform this cross, we can see that we're going to obtain A chance or a 1/2 chance of obtaining this sickle cell anemia genotype, which are going to be highlighted on the screen as we can see because of this answer choice. C heterozygous A being crossed with homozygous recessive A is going to be the correct answer to our question. I really hope this helped you and I hope to see you on the next one.

A 40-year-old woman whose father had Huntington disease currently shows no symptoms of the disease. She is newly pregnant with her first child and seeks your best estimate of the chance her child will inherit the disease. What is your estimate and how did you arrive at it? (Hint: See Figure 4.11)

Key Concepts

Autosomal Dominant Inheritance

Penetrance and Age of Onset

Risk Estimation Using Family History and Genetic Testing

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