1. Zaphod, a space alien from a planet near the star Betelgeuse, meets and marri

Question

1. 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 ? (1 mark) B] Earth phenotypes for nose, ears and arms? (1 mark) C] Alien nose and arms but Earth ears? (1.5 mark) D] Alien nose, but Earth arms and ears? (1.5 mark)

Explanation / Answer

According to the information, the alient father and earth's mother have offsprings with ut any genetic intereference. Here, it is very important to note that the map distance between the genes Q-B is 15mu and B-S is 20 mu. It must be recalled that according to Mendelian pattern of inheritance, two genes located less than 50 mu apart will be completely linked to each other and hence, will be inherited as a single unit despite the fact that other parent might contain other pair of alleles for those genes. Since the gene distance is very low, these genes will not show recombination at any place and hence will be inherited in the offsprings as it is.

According to the information, it must also be noted that the father's alleles are dominant over mother's alleles. Considering the fact that the distance between the alleles is too low to undergo recombination, these alleles will be inherited as a single unite due to complete linkage and all offsprings of this couple will be like father only.

Thus, based upon this explanation, answers can be found as below:

Part A: All (due to complete linkage)

Part B:None (Since Earth genotype is recessive to alient genotype)

Part C: None (no recombination will occur)

Part D: None (no recombination will occur)

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