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Biology Class 12 NCERT Solutions: Chapter 5 Principles of Inheritance and Variation Part 3
Q.5 Define and design a test β cross?
Answer:
- Test cross is a cross between an organism with unknown genotype and a recessive parent. It is used to determine whether the individual is homozygous or heterozygous for a trait.
- If the progenies produced by a test cross show 50% dominant trait and 50% recessive trait, then the unknown individual is heterozygous for a trait.
- On the other hand, if the progeny produced shows dominant trait, then the unknown individual is homozygous for a trait.
Q.6 Using a Punnett square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
Answer:
- In guinea pigs, heterozygous male with black coat colour (Bb) is crossed with the female having white coat colour (bb) .
- The male will produce two types of gametes, B and b, while the female will produce only one kind of gamete, r.
- The genotypic and phenotypic ratio in the progenies of F1 generation will be same i.e.. , 1: 1.
Q.7 When a cross in made between tall plants with yellow seeds (TtYy) and tall plant with green seed (TtYy) , what proportions of phenotype in the offspring could be expected to be
(a) Tall and green.
(b) Dwarf and green.
Answer:
A cross between tall plant with yellow seeds and tall plant with green seeds will produce
(a) Three tall and green plants
(b) One dwarf and green plant