In Exercises 21-28, find the probability and answer the questi...

Question

In Exercises 21-28, find the probability and answer the questions.

X-Linked Genetic Disease Men have XY (or YX) chromosomes and women have XX chromosomes. X-linked recessive genetic diseases (such as juvenile retinoschisis) occur when there is a defective X chromosome that occurs without a paired X chromosome that is not defective. In the following, represent a defective X chromosome with lowercase x, so a child with the xY or Yx pair of chromosomes will have the disease and a child with XX or XY or YX or xX or Xx will not have the disease. Each parent contributes one of the chromosomes to the child.

a. If a father has the defective x chromosome and the mother has good XX chromosomes, what is the probability that a son will inherit the disease?

Accepted Answer

Hello there. Today we're gonna solve the following practice problem together. So, first off, let us read the problem and highlight all the key pieces of information that we need to use in order to solve this problem. Males have the XY chromosomes, and females have the XX chromosomes. Capital X-linked recessive traits such as red, green color blindness appear when a defective X chromosome is not paired with a healthy capital X. Represent the defective X chromosome with lowercase x, so a child with lowercase x Y or Yx will express the trait. A child with X X X Y Y X X X or X X will not express the trait. Each parent passes one of their chromosomes to the child. What is the probability that a son will exhibit the trait if the father has the faulty X chromosome and the mother has normal XX chromosomes? Awesome. So it appears for this particular problem, we're ultimately trying to figure out our end goal of sorts is we're trying to figure out what the probability is that a son of a parent who has a father that has a faulty X chromosome, and a mother who has a normal pair of X X chromosomes, will be that the son will exhibit the trait that the father has. So the father has this recessive trait. That will result in the defective X chromosome that has the, that will lead to this color blindness. So, with that said, we're now trying to figure out the probability that's we're ultimately trying to solve for. So let's read off our multiple choice answers to see what our final answer might be. A is 0.25, B is 0.50, C is 0.75, and D is 0. Awesome. So first off, in order to solve for this particular problem, we need to understand the parent's chromosomes. So the father, which I'll denote as capital F, so the father has a lowercase X Y pair of chromosomes because they have a defective X chromosome. And our mother, which I'll denote as capital M, has two healthy X, both normal X chromosomes. Awesome. Our second step now is we need to determine the possible chromosome combinations for the sun. So the son must inherit the capital Y chromosome from their mother or father and a capital X, so they need a capital Y and a capital X chromosome from the other. But mothers always give a capital X chromosome, and fathers give either a X or Y for the sons. So from the mother, there will always give a X, and from the father, they will give a capital Y. So that means that so all sons will have the combination of, so let's make a note of this, so I'll make an and simple. So that means the sun, which I'll put an S in quotation marks, so the sun will have the combination capital X capital Y. Fantastic. So now our third step is we need to determine if the son will have this color blindness trait. So, since the mother gives a normal X chromosome, and the father gives a capital Y chromosome, the son's genotype will be X, Y, which will be, I'll put in parenthesis, a capital N for normal. So let's say that again. So, since the mother will give a normal X chromosome, and the father will give a Y chromosome, that will mean that the son's genotype will be XY, both capitalized, and this will be normal. So that will mean, as a result, the son will not receive the defective lowercase X chromosome. So the sun will not receive the defective XX chromosome. So that will mean, as a result for our 4th step, we need to make our final conclusions. So the probability of the sun having the trait, which I'll call SHT for short, so the probability of the sun having the trait will be equal to 0 because we know that the combination is going to result in a normal combination of X, Y chromosomes. And that will mean because it's a normal type, it will, the sun will not receive the defective X. So the final answer, without a doubt has to be 0, and this corresponds with multiple choice answer letter D, which once again is 0. Thank you so much for watching. Hopefully that helped, and I can't wait to see you in the next video. Bye.

Key Concepts

X-Linked Inheritance

Probability in Genetics

Punnett Square

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