In: Biology
A mouse from a true-breeding population with normal gait was crossed to a mouse displaying an odd gait called “dancing.” The F1 animals all showed normal gait. If dancing is caused by homozygosity for the recessive allele of a single gene, what proportion of the F2 mice should be dancers if you cross two F1 mice?
25%
50%
75%
0%
33%
The proportion of the F2 mice should be dancers when you cross two F1 mice = 25%
Let's assume a gene code for the gait character.
G - Dominant allele
g - Recessive allele
Here a true-breeding mouse with normal gait was crossed with a mouse with a dancing trait ( dancing is caused by homozygosity for the recessive allele).
parental genotypes: GG (Normal) gg (Dancing)
gametes: G g
F1 :
G | |
g | Gg(Normal gait) |
F1 Gg (Normal gait)
(From the F1 progeny, we can understand that normal gait is dominant over dancing).
The crossing of two F1 mice
F1 F1
Parental genotypes: Gg Gg
Gametes: G g G g
F2:
G | g | |
G | GG (Normal) | Gg (Normal) |
g | Gg (Normal) | gg (Dancing) |
Here, out of 4 chances, only one becomes a dancer. i.e., probability of dancers in F2 = 1/4 = 25%
The proportion of the F2 mice should be dancers = 25%