Question 1: Consider a diploid organism that has three pairs of chromosomes. Ass

Question

Question 1:

Consider a diploid organism that has three pairs of chromosomes. Assuming no crossing-over occurs, what proportion of gametes would be expected to ...

a. …contain chromosomes of maternal origin only?

b. … contain some chromosomes from both paternal and maternal origin?

Question 2:

Consider the two X-linked genes, z and w, in Drosophila. The two loci are 30 cM apart and each segregates a dominant allele (z+, w+) and a recessive allele (z, w). For each of the following crosses, predict the offspring’s phenotypic frequencies by sex?

a.            Heterozygous female in cis configuration x hemizygous z+w male.

b.            Heterozygous female in trans configuration x hemizygous zw male.

Please answer both parts of both questions for full points. Thank you.

Explanation / Answer

1a) Three chromosomes can be assumed as A, B and C. Each of the chromosome contributes maternal inheritance is 1/2 . Therefore, 1/2 x 1/2 x 1/2 = 1/8

b) Among A, B and C chromosomes contributing to both maternal and paternal would be AB and AC.

Hence, (1 - (1/8+1/8) ) = 0.9375 or approximately 3/4

2a)

Heterozygous female in cis configuration x hemizygous z+w male

z/z+ w+ x z+ w

z/z+w+ = 1/4

z/z+ z+ = 1/4

z/z+ w = 1/4

w+ w = 1/4

b) Heterozygous female in trans configuration x hemizygous zw male.

w/z+w+ x zw

w/z+ w+ - 1/4

w/z+ z - 1/4

w/z+ w - 1/4

w/w+ w - 1/4

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