Yellow bodies in Drosophila are caused by a mutant allele y of a gene located at
ID: 166979 • Letter: Y
Question
Yellow bodies in Drosophila are caused by a mutant allele y of a gene located at the tip of the X chromosome. (wild-type allele causes a brown-black body). A wild-type male is zapped with X rays (hint: known to cause chromosomal rearrangements like deletions, inversions, and translocations), then crossed with a yellow-(yy) female. Most of the male progeny were yellow, but two males were recovered which had dark bodies (y+). When these males were crossed to yellow females, the following results were observed:
Male # 1
Females all yellow, males all dark-bodied
Male # 2
Females: half yellow, half dark-bodied
Males: half yellow, half dark-bodied
a. At the cytological level, how did Male # 1 arise, and how does it account for the pattern of inheritance of his y+gene?
b. Explain what happened to the chromosomes of Male # 2 that accounts for the pattern of inheritance observed.
Male # 1
Females all yellow, males all dark-bodied
Male # 2
Females: half yellow, half dark-bodied
Males: half yellow, half dark-bodied
Explanation / Answer
Q.No a
The dark body male#1 is crossed with a yellow female yielding yellow female and dark male body, which is reversed sex linkage. If the e+ allele is tranloacted to the Y chromosome, then the dark male body would be XeYe+ or dark. When these are crossed with yellow females the result as follows:
XeY-e+ Dark Body Males XeXe Yellow females
Q.No b
The dark body male#2 is crossed with a yellow female, yielding dark and yellow males and females in equal proportions. If the e+ allele is translocated to an autosome, the resulting progeny as follows:
P Ae+/A; Xe/Y * A/AXe/Xe
F1 Ae+/A;Xe/Xe -- Dark Female
Ae+/A;Xe/Y -- Dark Male
A/A;Xe/Xe -- Yellow Female
A/A;Xe/Y -- Yellow Male
Where,
A - indicates an autosome involved in the translocation
“/” separates male and female contributions
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