It is given that when curly winged fly (Cc) mated with homozygous straight winged (cc) fly they deliver 50% curly winged (Cc) and 50% straight winged (CC) progeny. This means curly winged offsprings from cross 1 and 2 are heterozygous (Cc).
From cross 1 and cross 2 it is understandable that the eye colour is sex-linked (X chromosome-linked) recessive trait.
Let me discuss the crosses in brief:
1st white eye Xw (recessive)
Red-eye X (Dominant)
Male sex chromosome Y
Curly wing Cc
Straight wing CC
Now the 1st cross :
White-eyed straight winged male XwYCC x Red-eyed curly winged female XXCc
Male |
XwC |
YC |
|
Female |
|||
XC |
Xw XCC |
XYCC |
|
Xc |
Xw XCc |
XYCc |
Progeny: All red-eyed but 50% Curly winged Cc and 50% straight winged CC.
Now the 2nd cross :
Red-eyed curly winged male XYCc x White eyed straight winged female XwXwCC
Male |
XC |
Xc |
YC |
Yc |
|
Female |
|||||
XwC |
XwXCC |
XXwCc |
XwYCC |
XwYCc |
Progeny: All males are white eyed. All females are red-eyed. Half of each has a curly or straight wing.
Now, when curly winged (Cc) crossed with homozygous straight winged (CC) the cross is:
Curly |
C |
c |
|
Straight |
|||
C |
CC |
Cc |
50% curly and 50% straight winged offspring
Cross 3 :
Red-eyed curly winged male XYCc x Red-eyed curly winged female XwXCc
Male |
XC |
Xc |
YC |
Yc |
|
Female |
|||||
XwC |
XwXCC |
XwXCc |
XwYCC |
XwYCc |
|
Xwc |
XwXCc |
XXwcc |
XwYCc |
XwYcc |
|
XC |
XXCC |
XXCc |
XYCC |
XYCc |
|
Xc |
XXCc |
XXcc |
XYCc |
XYcc |
Phenotype:
Red-eyed curly winged male XYCc 2
White-eyed curly winged male XwYCc 2
Red-eyed straight winged male XYCC 1
White-eyed straight winged male XwYCC 1
Red-eyed curly winged female XwXCc/XXCc 4
Red-eyed straight winged female XwXCC/XXCC 2
The bold marking indicates the lethal effect of the gene.
If the ratios of the offspring are like above then the previous question illustrate recessive lethality (for wings) and the sex-linked inheritance (for eye colour)
But if the progeny show any other form (marked as bold) of a wing (cc) other than curly or straight, then its an example of incomplete dominance and sex linkage.
Please revert back if have any query
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