In guinea pigs, grey colour (GG) is dominant to white (gg) . Assorting on a different pairs of homologues, short hair (SS) is dominant to long hair (ss). In the parental generation, pure (homologous) grey, short-haired pigs are crossed to White, long haired pigs. In the F2 we expect ?
(1). Grey short in the proportion of ___
(2). White short in the proportion of___
(3). White long in the proportion of___
(4). ggSs progeny in the proportion of___
(5). GgSs progeny in the proportion of___
To determine the expected proportions of different phenotypes in the F2 generation, we can use the principles of Mendelian inheritance.
We are given that grey color (GG) is dominant to white (gg), and short hair (SS) is dominant to long hair (ss).
In the parental generation, the grey short-haired pigs are homozygous for both traits (GGSS), while the white long-haired pigs are homozygous recessive for both traits (ggss).
When these two parental genotypes are crossed, the resulting F1 generation will all be heterozygous for both traits (GgSs).
To determine the expected proportions in the F2 generation, we need to consider the possible combinations of alleles that can result from the cross between the F1 generation pigs.
(1) Grey short in the proportion of ___:
The grey color is dominant, so any pig with at least one G allele will exhibit grey color. In the F1 generation, all pigs are heterozygous (Gg) for color. When these heterozygotes are crossed, the possible genotypes in the F2 generation are GG, Gg, and gg. Therefore, the proportion of grey short-haired pigs in the F2 generation is 3/4 or 75%.
(2) White short in the proportion of___:
The white color is recessive, so a pig must have two copies of the recessive allele (gg) to exhibit white color. In the F1 generation, none of the pigs carry the gg genotype for color. Therefore, there will be no white short-haired pigs in the F2 generation, so the proportion is 0%.
(3) White long in the proportion of___:
The white color is recessive, and the long hair trait is also recessive (ss). The white long-haired phenotype can only occur if a pig has the genotype ggss. Since the white long-haired pigs in the parental generation are ggss, all the recessive traits will be passed on to the F1 generation. Therefore, the proportion of white long-haired pigs in the F2 generation is 100%.
(4) ggSs progeny in the proportion of___:
Since the parental generation white, long-haired pigs are ggss, all their offspring in the F2 generation will possess the genotype ggSs. Therefore, the proportion of ggSs progeny in the F2 generation is 100%.
(5) GgSs progeny in the proportion of___:
The F1 generation is heterozygous for both traits (GgSs). When these heterozygotes are crossed, the possible genotypes in the F2 generation are GGSS, GGss, GgSS, GgSs, Ggss, ggSS, ggSs, and ggss. GgSs is one of the possible genotypes, so the proportion of GgSs progeny in the F2 generation is 1/8 or 12.5%.