Consider the following pedigree. Assume individuals marrying...

Consider the following pedigree. Assume individuals marrying in do not carry the trait – but also note that individuals in the first generation are NOT marrying in (I-1, I-2) and may be any genotype. A. What is the most likely mode of inheritance for this pedigree? B. What is the probability that III-6 and III-7 had those children (in order left to right)? C. What is the probability that II-1 and II-2 have 4 more children – 3 unaffected daughters and one affected son?

Transcript

00:01 So i've done part of a pedigree for you here so we can examine what's happening and try to figure out genetically how we can label everything.

00:09 So first off, what i noticed that in this multi -generational family, the ones that are affected by this particular trait are almost all males.

00:23 So the fact that it's mostly males, almost entirely males, tells me that this is most likely.

00:31 A sex -linked trait.

00:36 Now, because we do have one female that's down here that does have this trait, it's not going to be in the x chromosome because then it wouldn't be possible for her to have it.

00:45 So that tells me that this is almost certainly on the x chromosome.

00:53 Now, because we have, say, in this first family, we have a dad who has this trait, and then of their children, you know, they have some daughters, a son and none of them have the trait.

01:13 Whereas in the second family, we have a father who has it, and then of their children, you know, the son has it and the daughter doesn't.

01:24 It looks like this is not going to be a dominant trait because it's not just wreaking havoc every time it's in a family.

01:32 So this is probably recessive.

01:37 So the way that i'm going to write it is x with a little r.

01:44 And if you have this, then you have the particular trait that we are tracking.

01:53 Okay, so given that information, i'm going to go ahead and label all of the people that are colored in that i know have the trait because they're easy.

02:01 Their x chromosome has this recessive trait on it, and then they have the y chromosome.

02:20 And then lastly, we have this female that does have the trait, so we would say that both of her x chromosomes have this recessive trait.

02:29 Okay, but this so far has been a guess.

02:32 If we are going to test this guess, then we need to go back through the family and write out what their genotypes would be to the best of our knowledge so we can see if this is even possible.

02:45 So first off, i'm going to start with this little family over here.

02:53 So this son has the trait that we're tracking because his one x chromosome has, the recessive trait.

03:07 Since this is a boy, we know he has a y chromosome, he can only get his y chromosome from dad, which means this recessive r trait on the x chromosome had to come from mom.

03:18 So we know that mom would have to have that recessive trait.

03:24 But since she doesn't have the recessive phenotype, we are saying that the other x chromosome has dominant trait on it...

Question

Please give Ace some feedback