Question

In Antirrhinum (dog flower), the phenotypic ratio in ${{F}_{2}}$ generation for the inheritance of flower colour would be
(a) 3:1
(b) 1:2:1
(c) 1:1
(d) 2:1

Answer 1

Hint: The ratio occurs in incomplete dominance where no factor of a gene is dominant causes a blend of dominant and recessive traits. The result of phenotype in ${{F}_{2}}$ is due to neither of the alleles being fully dominant over the recessive allele.

Complete answer:
The Antirrhinum shows incomplete dominance where the dominant allele form of a gene does not completely mask the effects of recessive alleles. Thus the flower of Antirrhinum blending of both alleles. It is also called semi dominance or partial dominance.

- The monohybrid cross between red and white dog flower where the allele that produces the red colour (R) is not completely expressed over the allele that produces the white flower causes offspring are all pink.
- When the red flower of genotype RR is crossed with white flower rr produces all pink colours offspring of genotype Rr in ${{F}_{1}}$ generation.
- The first filial generation consisting of all pink phenotypes is allowed to cross, where the resulting plants are second filial ${{F}_{2}}$ consist of three phenotypes.
One red cloud flower
Two pink colour flower
One white colour flower.
So, the correct answer is, ‘1:2:1.’

Note:
- When the ${{F}_{1}}$ generation is allowed to cross- pollinate with true- breeding red colours flower plants than the resulting ${{F}_{2}}$ generation plants consists of half red and half pink coloured phenotype flower.
- When the ${{F}_{1}}$ generation is allowed to cross- pollinate with true- breeding white colour flower plants than the resulting ${{F}_{2}}$ generation plants consist of half red and half pink coloured phenotype flower.