Genetic linkage mapping for a large number of families identifies 4% recombination between the genes for Rh blood type and elliptocytosis (see Problem 18). At the Rh locus, alleles R and r control Rh+ and Rh- blood types. Allele E producing elliptocytosis is dominant to the wild-type recessive allele e. Tom and Terri each have elliptocytosis, and each is . Tom's mother has elliptocytosis and is Rh- while his father is healthy and has Rh+. Terri's father is Rh+ and has elliptocytosis; Terri's mother is Rh- and is healthy.

What is the probability that the first child of Tom and Terri will be Rh− and have elliptocytosis?

Question

Genetic linkage mapping for a large number of families identifies 4% recombination between the genes for Rh blood type and elliptocytosis (see Problem 18). At the Rh locus, alleles R and r control Rh+ and Rh- blood types. Allele E producing elliptocytosis is dominant to the wild-type recessive allele e. Tom and Terri each have elliptocytosis, and each is . Tom's mother has elliptocytosis and is Rh- while his father is healthy and has Rh+. Terri's father is Rh+ and has elliptocytosis; Terri's mother is Rh- and is healthy.

What is the probability that the first child of Tom and Terri will be Rh− and have elliptocytosis?

What is the probability that the first child of Tom and Terri will be Rh− and have elliptocytosis?

Accepted Answer

Everyone. Let's take a look at this question together. What is the highest recombination frequency that may be seen in a genetic cross? If the two genes are on the same chromosome, is it answer choice? A 25% answer choice. B 50% answer choice C 70% or answer choice. D 100%. Let's work this problem out together to try to figure out which of the following answer choices is the highest recombination frequency that can be seen if the two genes are on the same chromosome. So we know that recombination events occur during meiosis. And we know that in meiosis homologous chromosomes pair up to exchange genetic material. And we know that when it comes to that frequency of recombination, when those two genes are close together on the same chromosome recombination is less likely. However, when those two genes are far apart, recombination is more likely. And in the case of them being far apart in that they are on opposite ends of the chromosome, the frequency of recombination is 50%. And since the opposite ends of the chromosome are the furthest apart, they can be. That means that the maximum recombination frequency is 50% since they cannot go further than the oppo ends of the chromosome. And the frequency when they are at opposite ends is 50% that means that the maximum is 50%. So answer choice, b 50% is the correct answer. Because the frequency of recombination between two genes on the same chromosome cannot exceed 50%. Because those recombination events occur during meiosis in which the homologous chromosomes pair up to exchange genetic material. And when the two genes are close recombination is less likely. However, when they're far apart, it is more likely. And the furthest apart that they can be is on opposite ends of the chromosome in which the frequency is 50%. So the highest recombination frequency that can be seen in the genetic cross if the two genes are on the same chromosome is 50% which is answer choice. B, the correct answer. I hope you found this video to be helpful. Thank you and goodbye.

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Key Concepts

Genetic Linkage and Recombination

Alleles and Dominance

Punnett Squares and Probability