How did they get the numbers at the end? 34%, 0.015, 0.06? Why did they use 0.68

Question

How did they get the numbers at the end? 34%, 0.015, 0.06? Why did they use 0.68/2*100=34%. Where did the 0.68 come from?

Here is the question

The father of Mr Spock is Vulcan, his mother is of terrestrial origin. A vulcan has pointed ears (determined by the allele P), adrenals absent (determined by A) and a right handed heart determined by R. All are dominant to earth alleles. The three alleles are atuosomal and are linked as shown

P______15 mu____A______20mu_____R

If Mr Spock marries an Earth woman, what portion of their children will be

a) Vulcan phenotypes for all 3 characters?
b) Earth phenotypes for all 3 characters?

c) Vulcan ears and heart but earth adrenals

d) Vulcan ears but earth heart and adrenals?

Explanation / Answer

Since the distance between P and A is 15 mu then

the probability of single crossover between them = 15/100 = 0.15

Likewise,

The probability of single crossover between A and R = 20/100 = 0.20

Hence,

The observed Double crossover frequency would be = 0.15 x 0.20 = 0.03

We know that most often double crossover resulted genotype would be same as the parental, therefore, the probability of the Vulcan and earth phenotype for all three character would be 0.03.

Vulcan ears and heart but earth adrenals manifest single crossover between A------R and a------r then frequency would be 20/100 = 0.20

Vulcan ears but earth heart and adrenals manifest single crossover between P-----A and p------a then frequency would be 15/100 = 0.15

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