The following pedigree illustrates the inheritance of...

The following pedigree illustrates the inheritance of Nance-Horan syndmome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth. a. On the basis of this pedigree, what do you think is the most likely mode of inheritance for Nance-Horan syndrome? b. If couple III-7 and III - 8 have another child, what is the probability that the child will have Nance-Horan syndrome? c. If III- 2 and III-7 were to mate, what is the probability that one of their children would have Nance-Horan syndrome?

The following pedigree illustrates the inheritance of Nance-Horan syndmome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth.
a. On the basis of this pedigree, what do you think is the most likely mode of inheritance for Nance-Horan syndrome?
b. If couple III-7 and III - 8 have another child, what is the probability that the child will have Nance-Horan syndrome?
c. If III- 2 and III-7 were to mate, what is the probability that one of their children would have Nance-Horan syndrome?

Key Concepts

Pedigree Analysis

This concept involves interpreting family trees to deduce how a trait or disorder is passed down through generations. It includes recognizing patterns of affected individuals, determining whether the trait skips generations, and observing any differences in male versus female transmission. Pedigree analysis is fundamental in identifying the mode of inheritance and estimating the probabilities of occurrence in offspring.

X-linked Inheritance

X-linked inheritance refers to genetic traits that are associated with genes found on the X chromosome. In many cases, these traits affect males and females differently because males have one X chromosome while females have two. The pattern may be characterized by a higher incidence in one sex, often with affected males more likely than affected females, making it a crucial concept when predicting the transmission of X-linked conditions.

Genetic Probability Calculations

This concept involves using principles of genetics, such as Punnett squares and probability theory, to estimate the likelihood that offspring will inherit a particular trait or disorder. It requires understanding how alleles are transmitted from parents to children and calculating the chances of each combination, which is essential for providing risk assessments in genetic counseling.

Transcript

00:01 Okay.

00:03 So here we're given a pedigree and we want to answer a few questions.

00:08 The first one is what's the mode of inheritance for this syndrome? and so the syndrome is represented in the red and we know that the square represents males and the circle represents females.

00:25 And because we're seeing only the disease or the condition in all these, red squares, that means we're only seeing it in males.

00:37 So there's something about the males.

00:40 And that tells us that it's sex -linked.

00:47 And now the question is, is it on the x chromosome or the y chromosome? and because we're seeing it only in males really here, that suggests that it's probably on the x chromosome, because the males only need one copy of this of this disease, we can call it a d here, one copy of it for them to get the disease.

01:14 Whereas if we had females, females would need two copies if i should preface.

01:19 This is if it's recessive.

01:23 And the females need two copies for them to get the disease.

01:26 So it's much easier for the males to get the disease.

01:29 And we can see how a female could be a carrier, like this female here with the x here.

01:35 She could be a carrier who is giving the male her male offspring of the disease.

01:43 So we can say this is x -linked recessive of a trait.

01:54 Okay, the next question is if couple seven in three, generation three, seven, and eight have another child.

02:01 What is the probability that they will have this syndrome? so we have to think about, um, we have to figure out what the genotypes of the parents are.

02:12 And so we can do that.

02:15 Pretty quickly.

02:17 Let's just erase this so we have more space here.

02:22 So i circled them in blue, the two that we want.

02:26 So these guys.

02:28 And so they have two children who are males who have this disease.

02:32 So if we think about we have this kind of punnet square and some of these children have the disease and these are the males.

02:40 So we can say they have x with the disease and y.

02:44 And this is like also the x with the disease and y.

02:47 So that means the mom must have, must be a carrier for this disease.

02:55 And this is because the dad only contributes the y chromosome.

03:00 So the dad is going to give the y chromosome here...