Wild-type mice are black. Crosses of pure-breeding parents produced the followin
ID: 63571 • Letter: W
Question
Wild-type mice are black. Crosses of pure-breeding parents produced the following F1 generations, and intercrossing the F1 from each cross gave the ratios shown for the F2 generation. The phneotypes are: Bl (black), Y (yellow), Br (brown), and W (white).
Cross
Parents
F1
F2
1
Bl x Br
Bl
3 Bl: 1 Br
2
Bl x Y
Bl
3 Bl: 1 Y
3
Br x Y
Br
3 Br: 1 Y
4
W x Br
Bl
9 Bl: 3 Br: 4 W
5
W x Y
Bl
9 Bl: 3 Y: 4 W
6
Bl x W
Bl
9 Bl: 3 Y: 4 W
A)From these results, determine the inheritance of these colors.
B) What are the genotypes of the parents, F1, and F2 offspring of each cross?
Cross
Parents
F1
F2
1
Bl x Br
Bl
3 Bl: 1 Br
2
Bl x Y
Bl
3 Bl: 1 Y
3
Br x Y
Br
3 Br: 1 Y
4
W x Br
Bl
9 Bl: 3 Br: 4 W
5
W x Y
Bl
9 Bl: 3 Y: 4 W
6
Bl x W
Bl
9 Bl: 3 Y: 4 W
Explanation / Answer
Cross 1: Cross between the parental genes, BIBI* brbr = all the progeny are BIbr (Black) ----> F1
Cross between F1 gives, BIbr* BIbr = BIBI, BIbr, BIbr, brbr = 3:1 (Black: brown).
Means BI is dominant to Br and it is an autosomal dominant inheritance.
Cross 3 also shows the same inheritance.
Cross 4 and 5: White and brown show complementation, that is, production of wild type phenotype when the two mutations are combined in a heterokaryon
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