Principles of Genetics and Breeding

Problems

1. In red tilapia, the allele for red body colour has an effect that is incompletely dominant over grey or black colour allele. If a cross between two tilapias produced 32 red, 68 pink and 28 black tilapias, what are the phenotypes of the parents ?

2. Calculate the ratios of body colour in red tilapia among the offsprings produced for the following crosses ?

a) red x red

b) red x pink

c) black x pink

d) pink x pink

3. When a transparent scaled (T’) goldfish is crossed to a normal scaled goldfish, all the progeny are calico type (T T’). From a cross of two such F₁s repeatedly made, the F₂ showed 6000 transparent scaled, 15000 calico and 5000 normal scaled goldfishes. How this trait is inherited? Give the genotypes of the parents, F₁ and F₂ progeny.

4. Give the genotypic and phenotypic ratio for the offsprings produced for the following crosses in the siamese fighting fish.

a) steel blue x steel blue

b) steel blue x blue

c) steel blue x green

d) blue x blue

e) blue x green

f) green x green

5. Three alleles determine the ABO blood type in brown trout, Salmo trutta fario. Alleles I^a I^a produces the A phenotype, I^b I^b produces the B phenotype, and I^o I^o produces O phenotype. The effects of I^a and I^b are dominant to O but are co dominant with each other. What are the genotypes of the following parents ?

Sl. No.	Phenotypes of parents	Phenotypes of offspring (proportions
		A	B	AB	O
1. 2. 3. 4. 5. 6.	B x B B x AB B x A B x A B x AB B x O	- - - ¼ ¼ -	¾ ½ ½ ¼ ½ 1	- ½ ½ ¼ ¼ -	¼ - - ¼ - -

6. In Tilapia, gold individuals were shown to be homozygous for the recessive allele (GG), while normal (wild) coloured individuals were homozygous for the normal (WW) allele (black colour) expression. Hetrozygotes (WG) displayed a “bronze” skin colour. Give the genotypic and phenotypic ratios for the offsprings produced among the following cross.

a) GG x WW

b) WG x WG

c) WG x WW

d) WG x GG