Question

In petunias, homozygosity for the P allele results in flat flowers, where homozygosity for the P’ allele results in curly flowers. Plants heterozygous for these two alleles have wavy flowers. How many plants out of a total of 200 resulting from a cross between two plants each having wavy flowers would be expected to have curly flowers?

		0.
		150.
		200.
		50.
		100.

Answer 1

50 plants with curly flowers.

Information given in question is that

PP = flat flowers (hmozygous for P allele )

P'P' = curly flowers (heterozygous for P and P' allele )

PP' = wavy flowers (hmozygous for P' allele )

When a croos made between two plants having wavy flowers (PP'), there are three types of offspring produced i.e., PP (flat flowers), PP' (wavy flowers) and P'P' (curly flowers) and there ratio would be 1:2:1 (1/4 plants with flat flowers, 1/2 plants with wavy flowers and 1/4 plants with curly flowers). We can see this in given Punnett square.

Hence, 50 plants out of a total of 200 resulting from a cross between two plants each having wavy flowers would be expected to have curly flowers.

	P	P’
P	PP	PP’
P’	PP’	P’P’

(200 x 1/4 = 50; 200 x 1/2 =100; 200 x 1/4 = 50)