Question

The father of Mr. Spock, first officer of the starship Enterprise, came from the planet Vulcan. Mr. Spock’s mother came from Earth. Pure-bred Vulcans like Mr. Spock’s father have pointed ears (P), no adrenal glands (A), and a right-sided heart (R) and are homozygous for all of these alleles. These Vulcan alleles are dominant over normal earthling alleles. These three genes are autosomal, and they are linked as shown in this map:

P__15 map units_________A_____20 map units________R

If Mr. Spock marries a woman from Earth, what is the likelihood (expressed as a percentage or as a decimal) that their children would:

a) have Vulcan traits for all three of these characteristics?

b) have Vulcan ears, earthling adrenal glands, and earthling heart?

c) have Vulcan ears, earthling adrenal glands, and Vulcan heart?

Answer 1

P          A           R

==============     (Spock)

p          a             r

            X

p          a           r

==============      (Wife)

p          a             r

a) We need to calculate P       A        R from Spock.

Need to calculate the percent of non-recombinant.

We know that 15% have CO between P-A.

We know that 20% have CO between A-R.

This crossover fragments include SCO plus DCO.

So, 35% recombinant, and this counts DCO twice.

If, no interference, DCO = .15 X .20 = .03 = 3 %.

So, total percent of recombinant children is 35% - 3% = 32%.

So, 68% are non-recombinant, meaning that 34% inherit P        A          R.

b) We need to calculate, how any inherit P       a        r

This is a SCO type of offspring. We calculate this as total CO frequency minus DCO, which is

15% - 3% = 12%

But this includes both SCO products.

So, percent of children inherit P       a        r is 6%.

c) We need to figure out percent that inherit P       a        R

This is a DCO type. DCO frequency = 3%.

So, 1.5% inherit P       a        R, which is one of two possible DCO products.