The pedigree below traces the inheritance of Marfan...

The pedigree below traces the inheritance of Marfan syndrome, a rare genetic disorder. 2 2 3 5 6 2 3 5 Question 5 Based on the pedigree provided above, determine the genotypes of the individuals indicated. 1. AA 2. Aa 3. aa 7_ What is the genotype of individual II-3? 4. $X^AX^A$ 6 What is the genotype of individual II-4? 5. $X^A X^a$ 6. $X^aX^a$ 7. $X^AY$ 8. $X^aY$ Question 6 0/1 point 0/1 point If individuals III-3 and III-5 had 3 children, what is the probability that all of their offspring will be affected? a) 0 b) 1/64 c) 1/8

Transcript

00:01 Pedigrees are always fun and they're particularly interesting when we get to figure out how a disease is being transferred in it.

00:08 And that's what we're going to walk through today.

00:10 In this example, there is a family which you can see in the pedigree that has marfan syndrome in it.

00:16 And we're asked, is this marfan syndrome sex -linked, autosomal dominant, or autosomal recessive? i'm going to start with sex -linked because sex -linked is the easiest one to identify or eliminate.

00:31 Because there's two options for sex -linked.

00:33 It could be connected to the y chromosome, and we know that females have two x chromosomes, males have one x and one y.

00:41 So if it was connected to the y, only males could get it, which clearly, according to the pedigree, is not the case.

00:48 So we know it's not y chromosome linked.

00:52 Could it be x chromosome linked? this family right here, and even this top one, tell me that it is not likely to be x -linked disease.

01:12 That is because, say in this first family, where the mom does not have the disease, so it is not on either of her x chromosomes, but the dad does.

01:25 So it is on his x chromosome.

01:31 When we look at their children, we see that any of their sons can't have the disease, can't be carriers at all, because any x chromosome they get from their mom is not going to be affected.

01:51 But number three here is their son and is affected.

01:55 So it is not going to be sex linked.

01:59 So it must be either autosomal dominant or autosomal recessive.

02:04 For both of these, the easiest way to tell is just to do some dihospalelial.

02:07 Hybrid crosses.

02:09 So we're going to start with autosomal dominant.

02:12 And if we're assuming autosomal dominant, it would mean that if you do have the disease, if the square or circle is colored black, they must have at least one dominant allele, the other may or may not be dominant.

02:25 But if they're not blacked out, then they must be homozygous recessive.

02:31 They can't have any dominant alleles.

02:36 All right, so we'll start with this first couple.

02:40 We'll make a cross for them.

02:44 So we know that the mom is not affected at all, so she's homozygous recessive.

02:49 However, the male has at least one dominant allele.

02:58 And since all of their children have the disease, we say it's likely that he's homozygous dominant.

03:08 And if we play that out, we see that 100 % of the disease, we say that's likely that he's homozygous dominant.

03:13 And if we say that it's likely that.

03:13 Their children would have one dominant allele so they would have the disease and that is what we see so we can continue on and see if this keeps going.

03:25 For the second couple, second family, which is going to be right here.

03:33 We know that the mother is a child of the first couple.

03:41 So she has to be heterozygous for this.

03:44 And the father does not have the disease...

Question

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