In guinea pigs, the gene for production of melanin is epistatic to the gene for
ID: 55480 • Letter: I
Question
In guinea pigs, the gene for production of melanin is epistatic to the gene for the deposition of melanin. The dominant allele M causes melanin to be produced; mm individuals cannot produce the pigment. The dominant allele B causes the deposition of a lot of pigment and produces a black guinea pig, whereas only a small amount of pigment is laid down in bb animals, producing a lightbrown color. Without an M allele, no pigment is produced so the allele B has no effect and the guinea pig is white. A homozygous black guinea pig is crossed with homozygous recessive white: MMBB × mmbb. Give the phenotypic ratio of the F1 and F2 generations.
Explanation / Answer
Genotype of F1 will be MmBb. M means melanin will be produced. B means lot of pigment will be deposited. So, all the F1 individuals will be black.
In F2 cross will be MmBb crossed with MmBb.
M_B_ = will be black. = 9/16
M_bb= will be light brown = 3/16
mm_B_ = white = 3/16
and mmbb = white.= 1/16
So, 9(black): 3(light brown): 4(white) will be the F2 phenotypic ratio.