Problems
1. The S gene in Tilapia aurea is an example of a dominant lethal gene. The gene S+ produces saddleback and the gene ++ produces normal fin. Find out the genotypic and phenotypic ratios for the following crosses. a) Saddleback x Saddleback b) Saddleback x Normal c) Normal x Normal 2. In common carp, a dominant gene (L) is lethal in homozygous condition. Produces light coloured pigmentation in heterozygous condition (Ll) and normal pigmentation in recessive condition (ll). What will be the phenotype for the F1 produced by a crossing of light coloured and normal pigmented fish ? 3. The genotypes and phenotypes of different varieties of common carp are mentioned below : SSnn, Ssnn - scaled or wild carp ssnn - “scattered” mirror SSNn, SsNn - linear mirror ssNn - “nude” or “leather” SSNN, SsNN and ssNN are non viable (lethal genes) Calculate the phenotypic and genotypic ratio of the offsprings produced from the following crosses of common carp. Also mention the phenotype of the parents. a) ssNn x ssnn b) ssNn x ssNn c) Snn x ssNn d) SsNn x ssNn e) SsNn x SsNn f) ssnn x ssnn 4.In gold fish, the gene M is epistatic with respect to the gene S. Genes m and s produce albino. The following combinations of genes are possible. MS and Ms-dark fishes, mS-light fishes, ms-albino fishes. By using the punnet square find out the phenotypic and genotypic ratio for the mating of the gold fish with following genotypes. a) Two heterozygous MmSs dark gold fish b) Mm Ss x mm ss c) MM Ss x mm ss d) MM Ss x Mm Ss e) Mm Ss x MM ss |