Neurofibromatosis 1 (NF1) is an autosomal dominant disorder in...

Question

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member. What is the estimated recombination frequency between the NF1 gene and the DNA marker? <
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Pedigree chart showing NF1 gene segregation with genotypes for a DNA marker in family members.

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Accepted Answer

Hey, everyone. Let's take a look at this question together. Marfan syndrome is a rare autosomal dominant condition affecting one in 5000 individuals caused by a mutation in a gene called F B N one mapping. The F B N one gene on chromosome 15 requires genetic linkage studies to test segregation of F B N one gene and DNA genetic markers on different chromosomes. A DNA marker comprising of two alleles denoted as one and two is linked to F B N one. The pedigree diagram given below gives the genotype of each family member. And here we have a pedigree diagram of two parents with six offspring and the genotype for each family member. Which of the following options gives the correct estimate of the recombination frequency of DNA markers among offspring. Is it answer choice. A 25% answer choice. B 50% answer choice C 75% or answer choice. D 100%. Let's work this problem out together to try to figure out what the correct estimate is for the recombination frequency of DNA markers among the offspring. So from the pedigree, we can see that we have two parents where the male parent is denoted by having a one and a two. And the female parent is denoted by having a two and a two. And we note that the two parents have six offsprings, which we can number one through six. And we want to know the recombination frequency of the DNA markers among the offspring. And the formula for recombination frequency is the number of recombinant divided by the number of offspring multiplied by 100. So now we need to determine the number of recombinant in the offspring, which we can identify that offspring. One, which is the female with the one and two de notion is a recombinant because it has a different combination of alleles than both of the parents as well as offspring two for the same reason. And we can also identify that offspring five, which is the male with the one and two de notion is a recombinant as well because it has the one allele from the father and the two allele from the mother, which means that we have 12 and three recombinant out of a total of six offspring. So our recombination frequency is equal to three, divided by six multiplied by 100 which is equal to 50%. So answer choice B 50% is the correct answer. Since three out of six of the offspring are recombinant which is 0.5 multiplied by that 100% to give us that 50% recombination frequency of DNA markers among the offspring. I hope you found this video to be helpful. Thank you and goodbye.

Key Concepts

Autosomal Dominant Inheritance

Recombination Frequency

Genetic Linkage Studies

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