Question

A breeder has observed variations in coat colour and pattern in the guinea pigs she has bred over the years. Black coat colour (B) is dominant over red coat colour (b), and white spotted pattern (s) is recessive to solid pattern (S).

a. What progeny will be produced from mating a male that is heterozygous black, and heterozygous solid with a red, homozygous solid female? Show the genotypes, phenotypes, and the phenotypic ratio

b. A third trait for coat type, where curly coat (C) is dominant over straight coat (c) is introduced. What offspring are expected from mating a female guinea pig (BBSsCc) with a male guinea pig (bbssCc)? Show genotypes, genotypic ratio, phenotypes, and phenotypic ratio. How many individuals are homozygous for curly coat?

Answer 1

a. The black coat colour (B) is dominant over red coat colour (b) and white spotted pattern (s) is recessive to solid pattern (S). Now when male with heterozygous black and heterozygous solid (BbSs) is mated with red homozygous solid female (bbSS), then the result of the cross is given below

Parents: BbSs (male) bbSS (female)

gametes: (BS) (bS) (Bs) (bs) (bS) (bS)

Offsprings; (BbSS), (BbSS), (bbSS), (bbSS), (BbSs), (BbSs), (bbSs), (bbSs)

Results:- 2 heterozygous black and homozygous solid (BbSS) (25%)

2 homozygous red and homozygous solid (bbSS) (25%)

2 heterozygous black and heterozygous solid (BbSs) (25%)

2 homozygous red and heterozygous solid (bbSs) (25%)

the phenotypic ratio is 1:1 (black solid:red solid) and the genotypic ratio is 1:1:1:1, with 50% parental combination (BbSs and bbSS) and 50% recombinant combination (BbSS and bbSs).

b. A third trait for coat type, where curly coat (C) is dominant over straight coat (c) is introduced. When a female guineapig (BBSsCc) is mated with a male guineapig (bbssCc), then the following results obtained as follows

Parents: BBSsCc (female)    bbssCc (male)

Gametes: (BSC) (BSc) (BsC) (Bsc) (bsC) (bsc)

Offsprings: (BbSsCC), (BbSsCc), (BbssCC), (BbssCc), (BbSsCc), (BbSscc), (BbssCc), (Bbsscc)

Results: 1 heterozygous black solid and homozygous curly (BbSsCC) (12.5%)

2 heterozygous black solid curly (BbSsCc) (25%)

1 heterozygous black and homozygous white curly (BbssCC) (12.5%)

2 heterozygous black curly and homozygous white (BbssCc) (25%)

1 heterozygous black solid and homozygous straight (BbSscc) (12.5%)

1 heterozygous black and homozygous white straight (Bbsscc) (12.5%)

the phenotypic ratio is 1:3:3:1 (black solid straight : black solid curly : black white curly : black white straight) the genotypic ratio is 1:2:1:2;1:1 (BbSsCC:BbSsCc:BbssCC:BbssCc:BbSscc:Bbsscc).

Number of individuals homozygous for curly coat is 2 (BbSsCC and BbssCC).