Principles of Genetics and Breeding

Problems

1. In goldfish, orange red colour (B) is dominant over blue (b) and normal eyes (D) over telescopic eyes (d). If the alleles segregate independently, write the most probable genotype for the parents for each of the following cross.

Sl. No.	Phenotypes of parents	Phenotypes of the offspring
		ORN	ORT	BN	BT
1. 2. 3. 4. 5. 6. 7.	ORN x ORN ORN x ORT ORT x BN BN x BN ORT x ORT ORN x ORT ORN x ORT	890 180 200 0 0 460 290	310 190 0 0 320 160 310	290 0 210 280 0 0 90	110 0 0 90 100 0 110

ORN– orange red normal,

BN– blue normal,

ORT– orange red telescopic,

BT–blue Telescopic

2. Normal spine in guppy is governed by a dominant gene (Sn) and curved spine by its recessive allele (Sc). Grey colour results from the action of the dominant genotype (G - ) and gold from the recessive genotype (gg). Determine the expected genotypic and phenotypic ratios in the progeny for the following crosses.

a) SnSc Gg x SnSc Gg

b) SnSc GG x ScSc Gg

c) SnSc gg x SnSn gg

d) ScSc gg x ScSc gg

3. In the case of minnows Grey-green (G) colour is dominant to pink colour. Normal fin (N) is dominant to long fin (n). If a homozygous Gray-green with normal fin male minnow is crossed with a homozygous pink and long fin female What will be the genotypes and phenotypes of the F₁ and F₂ offsprings.

4. In the case of Nile tilapia, two loci A and B are involved in producing normal body colouration. The recessive alleles a and b in combination, and only in combination, would result in pearl colouration. Either recessive allele, when present alone, would not alter the normal colouration of the fish. Determine the expected genotypic and phenotypic ratios in the progeny from the following mating.

a) AA BB x aa bb

b) Aa Bb x Aa Bb

c) Aa BB x AA Bb

d) aa Bb x aa Bb