The father of Mr. Spock, first officer of the starship Enterprise, came from pla
ID: 148603 • Letter: T
Question
The father of Mr. Spock, first officer of the starship Enterprise, came from planet Vulcan; Spock's mother came from Earth. A Vulcan has pointed ears (determined by allele P), adrenals absent (determined by A), and a right-sided heart (determined by R). All these alleles are dominant to normal Earth alleles. The three loci are autosomal, and they are linked as shown in this linkage map:
If Mr. Spock marries an Earth woman and there is no (genetic) interference, what proportion of their children will have
a.
Vulcan phenotypes for all three characters?
b.
Earth phenotypes for all three characters?
c.
Vulcan ears and heart but Earth adrenals?
d.
Vulcan ears but Earth heart and adrenals
Explanation / Answer
Answer: Part A.
This problem is solved two ways, once in the standard way, once in a way that emphasizes a more mathematical approach. The cross is: the outline of the P and F1 generations is the same in both editions. a.In order to find what proportion will have the Vulcan phenotype for all three characteristics, we must determine the frequency of the parentals. Crossing over occurs 10 percent of the time between Pand A, which means it does not occur in 90 percent of the time. Crossing over occurs 25 percent of the time between Aand R, which means that it does not occur 75 percent of the time. p(no crossover between either gene)=p(no crossover between P and A) x p(no crossover between Aand R) = (0.9)(0.75)=0.68 Half of the parentals are Vulcan, so the proportion that are completely Vulcan is ½(0.68)=0.34. Mathematical method: Number of parentals = 1- (single CO individuals – DCO individuals) = 1 - 0.10+0.25 – 2(0.10)(0.25) - (0.1)(0.25) = 0.68 Because half the parentals are Earth alleles and half are Vulcan, the frequency of children with all three Vulcan characteristics is ½(0.68) = 0.34.
b. Answer is identical in both editions .
c. worded answer is identical in both editions. Calculation reads like this: ½ (0.1)(0.25)=0.0125. d. worded answer is identical in both editions. Calculation reads like this: p (CO P - A ) x p (noCO A-R ) = (0.1)(0.75) = 0.75
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