Zaphod, a space alien from a planet near the star Betelgeuse, meets and marries

Question

Zaphod, a space alien from a planet near the star Betelgeuse, meets and marries a phenotypically normal Earth woman, Jane. Interestingly, Zaphod himself has a father from his home planet and a human mother. Aliens from the Betelgeus region like Zaphod have pointed noses (specified by allele Q), purple ears (specified by B), and extra long arms (specified by S). All three alleles are dominant to corresponding wild type Earth alleles. The three gene loci are located on autosomes. The three genes are known to have the linkage arrangement where gene B is in the middle of Q and S with the Q-B distance equal to 15 mu and the B-S distance equal to 20 mu. If Zaphod and Jane have children, and there is no genetic interference, what proportion will have:

A] Alien phenotypes for nose, ears and arms ?

B] Earth phenotypes for nose, ears and arms?

C] Alien nose and arms but Earth ears?

D] Alien nose, but Earth arms and ears?

Explanation / Answer

Zaphod's father is alien with genotype : QQBBSS

Zaphod's mother is human with genotype : qqbbss

Zaphod genotype : QqBbSs

QBS are dominant to qbs

Zaphod x Jane

QqBbSs x qqbbss

Possible genotypes are : QBS, qbs, QBs, Qbs, QbS, qBS, qbS, qBs

Total map units = 35

35 m.u = 35% recombinant genotype

remaining 65 % parental genotype (QBS ans qbs)

Parental phenotype (2)

A] Alien phenotypes for nose, ears and arms : QBS: 1/2

1/2 x 65 = 32.5 %

B] Earth phenotypes for nose, ears and arms : qbs : 1/2

1/2 x 65 = 32.5 %

Recombinant phenotype (6) : QBs, Qbs, QbS, qBS, qbS, qBs

C] Alien nose and arms but Earth ears : QbS : 1/6

1/6 x 35 = 5.833 %

D] Alien nose, but Earth arms and ears : Qbs : 1/6

1/6 x 35 = 5.833 %

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