Female Drosophila melangaster that are homozygous for the X-linked, recessive wh
ID: 52251 • Letter: F
Question
Female Drosophila melangaster that are homozygous for the X-linked, recessive white eye allele and the autosomal, dominant normal wing shape allele are crossed eith males that carry the X-linked, dominant red eye autosomal recessive vestigial wing.
1) WHat is the proportion of female F2 progeny that are white eye and vestigial wing?
37.5%
25%
12.5%
From my understanding the parents are xrxrNN x xRyNn (n=normal wing and r(superscript=White eye). When crossed these I could not fiigure out which F1 progeny to cross to get the F2 progeny as I got two different types of girls adn two different types of guys. Could you please explain how to get teh F2 progeny????
Explanation / Answer
In Drosophila, the chromosomal basis of sex determination is due to the ratio of X chromosomes to sets of autosomes i.e. the X/A ratio. A normal Drosophila with 2 X chromosomes (XX AA) has an X:A ratio of 1.0 and is phenotypically female. A normal Drosophila with a X and a Y chromosome (XY AA) has an X:A ratio of 0.5 and is male.
So, the X-Y method of sex determination does not help here.
XR= X linked dominant red eye allele
X= X linked recessive white eye allele( XR > X)
N= normal wing allele
n= recessive wing allele (N> n)
female XXNN * XR0nn male
gametes XN XRn 0n
F1 XRXNn ( female with red eye & normal wing) & X0Nn (male with white eye & normal wing)
They are crossed for F2 progenies
F1 XRXNn * X0Nn
Gametes XRN, XRn, XN, Xn XN, Xn, 0N, 0n
Do a Punnett’ square
Male/female
XRN
XRn
XN
Xn
XN
XRXNN
fem, red, normal wing
XRXNn
fem, red, normal wing
XXNN
fem, white, normal wing
XXNn
fem, white, normal wing
Xn
XRXNn fem, red, normal wing
XRXnn
fem, red, recessive wing
XXNn
fem, white, normal wing
XXnn
fem, white, recessive wing
0N
XR0NN
Male, red, normal wing
XR0Nn
Male, red, normal wing
X0NN
Male, white, normal wing
X0Nn
Male, white, normal wing
0n
XR0Nn
Male, red, normal wing
XR0nn
Male, red, recessive wing
X0Nn
Male, white, normal wing
X0nn
Male, white, recessive wing
Hence, out of 16 progeny, 8 are female and 8 are male
Out of 8 female progeny, 1 is white eyed and vestigial winged.
Hence, proportion = 1/8 * 100 = 12.5 %
Male/female
XRN
XRn
XN
Xn
XN
XRXNN
fem, red, normal wing
XRXNn
fem, red, normal wing
XXNN
fem, white, normal wing
XXNn
fem, white, normal wing
Xn
XRXNn fem, red, normal wing
XRXnn
fem, red, recessive wing
XXNn
fem, white, normal wing
XXnn
fem, white, recessive wing
0N
XR0NN
Male, red, normal wing
XR0Nn
Male, red, normal wing
X0NN
Male, white, normal wing
X0Nn
Male, white, normal wing
0n
XR0Nn
Male, red, normal wing
XR0nn
Male, red, recessive wing
X0Nn
Male, white, normal wing
X0nn
Male, white, recessive wing
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