Principles of Genetics and Breeding

Problems

1. A dominant allele G produces grey guppies. Its recessive allele g produces gold guppies. A group of homozygous grey guppies and gold guppies were crossed and their F₁ progeny were then test crossed. Determine the expected genotypic and phenotypic ratios among the test cross progeny.

2. In the case of goldfish, the cross of normal eye X telescopic eye yields normal and telescopic eyed progeny in equal proportions, but telescopic eyed X telescopic eyed always gives rise to only the telescopic eyed progeny. What does this tell about the genotype of normal and telescopic eyes in goldfish ? Which phenotype is dominant?

3. The colour of the parent and offsprings of grass carp is given below. Explain the results for the crosses and mention the genotypes of all the individuals.

Sl. No.	Parents	Progeny colouration
1.	Wild x Wild	Wild
2.	Wild x Albino	Wild
3.	Albino x Wild	Wild
4.	Albino x Albino	Albino
5.	Albino x Wild	530 Wild, 480 Albino

4. Normal eyes of gold fish is a dominant trait. Telescopic eyes is the alternative recessive trait. When a pure normal eye gold fish is crossed to a telescopic one,what fraction of F₂ is expected to be heterozygous ?

5. In carp, blue colour is recessive to non blue colour. What coloured carp will you choose to breed a given non blue colour fish in order to find its genotype ? Write the type of cross ?

6. Koi carps with known phenotype but with unknown genotype produced the listed progeny.

Sl. No.	Parents	Offsprings
		Pattern	No pattern
1. 2. 3. 4. 5.	Pattern x No pattern Pattern x Pattern No pattern x No pattern Pattern x No pattern Pattern x Pattern	820 1180 0 3500 2800	780 390 1500 0 0

Using D for the light yellow pattern gene and d for no pattern give the most probable genotype of each parent.

7. In carps blue colour is recessive to non-blue colour. A non blue colour carp male has blue colour female parent.
8. What is the genotype of the fish and female parent ?

What are the possible genotypes of male parent ?

If the fish is crossed with a blue coloured female, What are the possible genotypes of their offsprings ?

8. Two light yellow pattern Japanese carps on breeding produce 1678 light yellow pattern and 554 no pattern offsprings. Give the genotypes of the parents and justify your answers with reasons. (Given : Light yellow pattern is dominant to no pattern). If a pure light yellow pattern carp is crossed with a hybrid light yellow pattern, what will be the genotypic ratio of the offsprings ?
9. When a red Medaka was crossed with wild type, the offspring were all wild type (green), but when these offspring were crossed among themselves the result was approximately three greenish offspring to one red. Explain dominant and recessive colour in Medaka. What is the type of inheritance in Medaka?.
10. A dominant gene ‘+’ is responsible for the normal pigmentation of body colour in catfish; its recessive allele ‘a’ produces albino. A testcross of a normal type female gave 5200 normal and 5500 albino in the F₁. If the normal F₁ females are crossed to their albino F₁ brothers, What genotypic and phenotypic ratios would be expected in the F₂? Diagramme the results using the appropriate genetic symbols.