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 chance II-4 has the disease?

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 chance II-4 has the disease?

Pedigree chart showing family members with an autosomal recessive disorder and VNTR genotypes.

What is the chance II-4 has the disease?

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together an autosomal recessive disorder with a Lil's capital A and lower case A has been linked to a V N T R. The recombination frequency of the disease gene and the V and T R is 10.7%. The accompanying pedigree shows a two generation family in which the disease is present. The V and T R has two allys V one and V two and the gel electrophoresis pattern of each family member has been shown below. I will describe these images and results in a second. But for now, let's look at what the question asks based on this information. What is the genotype of the fifth individual of the second generation for V N T R? The answer options are a V 1, V BV 1, V 2 CV two, V two and D can be either V one V one or V one V two. So let's go back up and take a look at the pedigree and gel results. The pedigree is a two generation family. There are two parents in the first generation that are unaffected by the autosomal recessive disorder. They have five in five Children of which the first individual is affected by the disorder. Individuals, 23 and four are unaffected. And the fifth individual information is not given the gel electrophoresis results are given by testing samples from each individual. The image shows the wells on the gel electrophoresis. Then it shows whether bands are present for the two V N T R all lies B one and B two alis migrate through the gel at different speeds. And V two moves faster than V one. Therefore, individuals with a band on the top have the V one A lil and individuals with a bottom band have the V two A lil. Both parents in the first generation have both V one and V two bands. Individual, one of the second generation only has a V two band individual. Two of the second generation only has a V one band. Individuals three and four have both V one and V two bands and the fifth individual has only a V two band. So let's review some information. The autosomal recessive disorder we are told is linked to a V N T R which stands for variable number tandem repeat. These are locations of short repeated nucleotide sequences. And we are also told that there are two lies V one and V two for that V N T R. Now the question remember asks us to determine the V N T R genotype for the 5th individual in the second generation. So we're determining what ails, whether it's V one and or V two are present for this individual. So we will focus more on the gel electrophoresis results. Since it gives information about those V one and V two ails, the gel results show that individual five of the second generation has only the V two band. This means that only the V two A lil is present. Therefore, because a genotype must include two. Ails. His genotype is V two V two. That means the correct answer is option CV 2 V 2. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

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Key Concepts

Autosomal Recessive Inheritance

Variable Number Tandem Repeats (VNTR)

Recombination Frequency