The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family.
What is the genotype of each family member, including II-4, for the VNTR?

Question

The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family.

What is the genotype of each family member, including II-4, for the VNTR?

Gel electrophoresis results displaying VNTR genotypes for family members in a genetic study.

What is the genotype of each family member, including II-4, for the VNTR?

Accepted Answer

Hello, everyone. Welcome back. Here's our next problem. It says and autism or recessive disorder with a little big A and little A has been linked to a V N tr. The recombination frequency of the disease gene and the VNTR is 10.7%. The accompanying pedigree shows a two generation family in which the disease is present. The V N tr has two alleles V one and V two and the gel electrophoresis pattern of each family member has been shown below. And then we're presented with two figures here. One is the pedigree mentioned in the question and one is an electrophoresis gel with a sample from each family member. Um And then I'm going to scroll down words here because this doesn't all fit to get to the question itself and the answer choices. And it then says based on this information, identify the genotype of Roman numeral 2-5 for the disease gene. Our answer choices being choice. A big, a big A choice. B big, a little A choice, C little, a little A or choice D can be either a big, a big A or big, a little A. So we're presented with information about two different genetic pieces of information, a disease gene with all those big and little A and then these V N T R s with two different alleles, scroll back up to our question. So let's recall what A B N tr is. And that stands for variable nucleotide tandem repeats. And these are different lengths of repeated DNA sequences. So you can have a specific DNA sequence repeated five times or 10 times or 16 times. And each different length or different number of repeats is a different alley. All these vary from individual to individual and therefore, can be used to distinguish between individuals. Um although they are inherited, so they're going to be similar based on um a person's relatedness to another person. In this case, we're just talking about two different lengths because we're talking about two alleles V one and V two inherited by these different family members. And because they're different sized pieces of D N A when they're run on a gel, the DNA is cleaved by restriction enzymes that cut it at either side of the V N tr. And so because there are different lengths, the fragments will be different sizes and so it can be separated by running a gel. So with that in mind, let's work through what we have here. We've got a lot of information being thrown at us. Um kind of kind of systematically work through what we're looking at here. And before we even start to analyze the figures were given, let's think about the information given at the beginning of the problem about the gene linkage and what that means. So basically, we're talking about two genes are disease gene with its big, a little a alleles, it's recessive. So we know that any affected family members must be homos, I guess recessive. I'm gonna scroll down now a little bit and we have our V N tr Alleles of V one and V two. These jeans are pretty closely linked. We see that the recombination frequency we're given is 10.7% recombination frequency of 50% means that either they're on separate chromosomes or they're so far away that they recombine frequently or freely. Um 10.7 is pretty low and so our genes are fairly closely linked. So in general will be inherited together. So if an individual has big A and V one, Most likely the offspring will inherit big A and B one together. So with that in mind, let's turn our attention to the figures were given here that will scroll down. So they both fit. So first, we have our pedigree, we have two generations, generation, one is our parents. So two individuals both unaffected. So we know that these individuals are either homesick is dominant or heterocyclic. However, then we have our second generation moment in world to their five Children, child, number one or individual number one is affected by the disease, then 23 and four are unaffected. And then number five is our question mark that we're trying to determine. So now we know because our disease is recessive and we have one child that is affected, the parents must both be hetero six carriers of this gene. So I'm going to right above each of the parents big a little a as I know that must be their genotype for the disease. Now, we're also given our information about this V one V two. Well, we're given this information because we're supposed to figure out what the genotype is for individual five, for whom we've not been given the phenotype. So we don't have that to go on. So we're going to have to look at the linkage between R V N T R and R disease gene. And then we can use the gel information to reason backward to our disease gene genotype. So our second figure is our electrophoresis gel. It's got a sample for every individual on the pedigree showing whether they have a band for V1 V2 or both. So let's start with the parents and see what their V N T R genotype is. While parent, number one and number two, we know they're both hetero sickness for the aging. And we see when we look at our gel that they have bands for V one and V two, both of them. So both of them are hetero sickness for the V N tr as well. So they're big a little a and then their V one V two, I'm going to write that in next to their, a genotype above their symbol on the pedigree. So that lets us know that um, they're headers, I guess for both traits, but we don't know which is big a link to V one, little, a link to V one. We don't know, but we might get a clue by looking at our offspring and seeing what's different in their vien tr pattern based on their genotype. Well, we do know one individual's genotype for certain in generation two And that is our affected individual Roman numeral 2- because this is recessive. We know that this individual must have a little, a little a as their disease genotype. So let's look at what their V anti R genotype is. When we look at that sample on the, well, for Roman in world 2-1, they have no band for V one, just a band for V two. So therefore that little a little a genotype comes with a V two V 2 genotype. So that indicates that the little A gene and the V two or a little a little and the V two allies are linked together. And then we can assume that the big a little and the V one gene are linked together as well. Now, a complicating factor here could be if the two parents have a different linkage from each other. So perhaps in parent, one big A's linked with the one and parent too big is linked with the two. Um We can see and get a clue about this by looking at our other individuals. So numbers 2, 3 and four in generation two and looking at their VNT Arjuna types, we know they have to be either hetero Ziegesar homos, I guess dominant since they're all unaffected. So let's look at individual Roman in world 2- that they're gel pattern. And we see that this individual has only a V one band, no V two band. So this individual must be big a and then we'll just put blank because we don't know the second value is But then V one, V 1. Well, this seems to indicate that it would be a good guess that this individual is homos, I guess dominant With that big a being linked to the V- one alil in all these cases. Let's look at individual number three. When we look at that gel sample, We see a band for V one and a band for V two. So we're going to see an individual three is hetero sickness for big a little, a little a along with being hetero ziggy's for V one V two. And then number four, Roman world 2-4 also shows both a V one and V two band. So we're gonna say big a little A and then V one V two as the genotype for individual four. So now let's think about our mystery individual number five. Let's look at the gel pattern for Roman and World 2-5. And we see that this individual has no gel band for V one only for V two. So this individual is V two, V two for the VNT are. So based by the pattern we've seen in this individual siblings, we are going to guess that the disease genotype is little a little a. So let's scroll down to our answer choices and that is going to be choice. E little a little A based on that linkage we established between the big a little and the V one a little, the little a little and the V two a little based on the patterns we see with the other individuals. So again, based on the information we've been given, identify the genotype of Roman Roman numeral 2-5 for the disease gene choice C little a little a see you in the next video.

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Key Concepts

Autosomal Recessive Inheritance

Variable Number Tandem Repeats (VNTR)

Gel Electrophoresis