The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.
From these data, can you conclude that Rh and elliptocytosis loci are genetically linked in this family? Why or why not?

Question

The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.

From these data, can you conclude that Rh and elliptocytosis loci are genetically linked in this family? Why or why not?

Lod score graph showing the relationship between theta values and genetic linkage for Rh blood group and elliptocytosis.

From these data, can you conclude that Rh and elliptocytosis loci are genetically linked in this family? Why or why not?

Accepted Answer

Welcome back. Let's look at our next problem. It says the values of the recombinant frequencies of different gene pairs are given as follows Ac 50% BC, 30% BD, 12%. Which of the following statements about the link gene is true based on the data presented above. And our statements are a gene A is very close to gene C B. Gene B is very close to gene D choice C genes A and D are more closely linked than others or D genes B and C are a greater distance apart than others in questions like this. That's good to sort of start with a tentative map. We're recalling from our content video that recommit frequencies are proportional to the physical distance. Genes are apart on the chromosomes. So we can essentially use them as a measure of distance. I always like to start with the largest distance apart and set those two genes at either end of my tentative segment. I might have to put other genes on the outside depending on which side of my starting genes they're on. But I just find it easier to start with the largest distance. So in that case, that's the distance between A, the recoin frequency um between A and C is 50% which is the highest number. So I'll draw a line here with a, at the left side, see at the right side, and I'm going to label this distance 50%. Now, we'll look at our other recombinant frequencies to map the other genes with relation to A and C. So my next largest is BC, which is 30%. But I actually like to start with a smaller distance uh as I put things apart. So my smallest distance is 12%, but that's between B and D, neither of which I have on my line yet. So we'll go back to BC 30%. Well, I have C on my line. So that tells me that B is a distance of 30% from C. So I'll start by putting B in the middle between A and C. It might have to end up on the other side when I put everything together, but I'll start with it in the middle. So with C on my right side, I'll put B sort of more than half a little more than halfway between C N A and I'm gonna label that distance Between B&CS 30%. And then I have that the distance between B&D is 12%. Well, I've tentatively put B here in the middle. So I'm going to put, and I, I know that B and A then since I have my 50% between A and C, 30% between B and C, the distance between A and B would then be 20%. So I will tentatively put D in between B and A. So we'll put, uh, D here sort of more than halfway between B N A and then the distance between B and D is 12%. And I don't see any contradictory evidence to this linkage here. So I'll then label that distance between A and D. Since I know that A to B is 20% D two B is 12% I'll Tenn label that A through D distin 8%. So my map puts them in the order AD BC. So let's evaluate our statements here. Choice A says, Gene A is very close to gene C. Well, that's not true because they have the greatest distance between them at 50%. So we'll eliminate that. Choice. B says Gene B is very close to gene D. Uh Well, it is close. It's just 12%. There is a smaller distance between A and D of 8%. So I'm going to kind of put a little dot Next to Choice B. That may be my correct answer. But I'd like to see if there's a better statement choi says, genes A and D are more closely linked than the others. And A and D I have a tentative distance of 8%, which is the smallest distance of any list on my map. So that would definitely be true. They are more closely linked than others. So I'm gonna go ahead and circle, see and assume that's my answer. That choice B which described GB as very close to Gene B very close is a nebulous term. What exactly does that mean? So since choice C is definitely true, I will go ahead and erase my little dot And cross out choice B and then finally, choice D says genes B and C are a greater distance apart than the others. They are the second greatest distance at 30% but not as large a distance as that between A and C at 50%. So choice D is definitely not correct. So again, given these recombinant frequencies, which of the following statements about the linked gene is true and that would be choice C. Genes A and D are more closely linked than others. See you in the next video.

Verified video answer for a similar problem:

Key Concepts

Genetic Linkage

Lod Score

Autosomal Dominant Inheritance