Question 12 0 3 pts a couple who are about to have children...

Question 12 0 / 3 pts A couple who are about to have children discover they each had a single grandparent whose sibling was affected with cystic fibrosis (a rare autosomal recessive disease). If the couple has a child, what is the probability that the child will have cystic fibrosis? 0. 021 You Answered 1. 025 2. 004 Correct Answer ○ 0. 007 Ο 0.015

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00:01 Okay, so in both these parents ' families, their unaffected grandparents had siblings with cystic fibrosis.

00:07 Their great -grandparents were unaffected, and we want to know the probability that the child will have cystic fibrosis.

00:15 So if the couple marries and has a child, what is the probability that the child will have cystic fibrosis? i'm going to call this question a.

00:24 So the unaffected siblings, i'm not going to write that.

00:31 So the unaffected siblings have a two -thirds chance of being heterozygous.

00:36 Therefore, each person has two -thirds times one -half times one -half again.

00:45 So a one -and -sixth chance of being heterozygous carriers.

00:58 So if both heterozygous, then there is a one -fourth chance of passing the recessive genes.

01:06 So one -fourth chance.

01:12 So b states if they have four children, what is the chance that the children will have the precise mendelian ratio of 3 to 1 for normal cystic fibrosis? so four children with a 3 to 1 ratio would mean that 3 normal and 1 abnormal.

01:31 So normal, and i use that word likely, but you know, you get the point, occurs 3 fourths of the time, and abnormal occurs.

01:49 One -fourth of the time.

01:51 So we want to know what is the probability of this happening.

01:55 So let's do some math...

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