Question

Suppose you have a plant with petals that are normally blue. Suddenly you see some white-petaled plants. Cross 1: You cross the white with the blue and you get all an F1 population that is all blue. In the F2 generation you see a ratio of 101:33 blue to white-petaled plants. Another line of flowers shows pink petals. Cross 2: You cross the pink with the blue and once again the F1 generation shows all plants with blue petals. However, in the F2 generation the ratio is 192:63 blue to pink- petaled plants. Cross 3: You cross the pink and the white. You get all blue in the F1 generation. Cross 4: You cross the F1 individuals obtained from cross 3 and the F2 generation shows a segregation of 272:121:89, blue to white to pink-petaled plants. Which of the crosses above represent an example of complementation. Check all that apply. Cross 1 Cross 2 ✓ Cross 4 Cross 3

Answer 1

Answer-

According to the given question-

Complementation – is defined as a condition when two strains of an organism having different homozygous recessive characteristics are producing the same phenotype then this is called complementation.

Here we have a condition where the blue color petals are normally occurred in the population and are dominant, but we also observed some white color petals.

Cross 1-

When we make a cross between the Blue petals with the white petals, then in the F1 generation we get all the offspring having blue petals. but when we make a self crossed between the offspring of the F1 generation we get the 101: 33 (Blue: White) in the F2 generation.

Suppose the allele for Blue color petals = B

the allele for white color petals = b

The genotype of Blue color petals = BB

The genotype of white color petals = bb

Cross between BB $\times$ bb

	b	b
B	Bb (Blue color petals)	Bb (Blue color petals)
B	Bb (Blue color petals)	Bb (Blue color petals)

All the offspring of the F1 generation will have blue color petals.

A self cross between the offspring of the F1 generation-

Cross between Bb $\times$ Bb

	B	b
B	BB (Blue color petals)	Bb (Blue color petals)
b	Bb (Blue color petals)	bb (White color petals)

Then in the F2 generation, we get the ratio of 3: 1 of blue: white

but the observed number of offspring -

Blue color petals = 101

White color petals = 33

Total = 101 + 33 = 134

Expected Number of offspring -

Blue color petals = 3 $\div$ 4 $\times$ 134 = 100.5

White color petals = 1 $\div$ 4 $\times$ 134 = 33.5

So the number of observed offspring is close to the number of expected offspring, i.e. in the ratio of 3: 1.

Cross 2-

When we make a cross between the Blue petals with the pink petals, then in the F1 generation we get all the offspring having blue petals. but when we make a self crossed between the offspring of the F1 generation we get the 192: 63 (Blue: pink) in the F2 generation.

Suppose the allele for Blue color petals = B

the allele for pink color petals = b

The genotype of Blue color petals = BB

The genotype of pink color petals = bb

Cross between BB $\times$ bb

	b	b
B	Bb (Blue color petals)	Bb (Blue color petals)
B	Bb (Blue color petals)	Bb (Blue color petals)

All the offspring of the F1 generation will have blue color petals.

A self cross between the offspring of the F1 generation-

Cross between Bb $\times$ Bb

	B	b
B	BB (Blue color petals)	Bb (Blue color petals)
b	Bb (Blue color petals)	bb (pink color petals)

Then in the F2 generation, we get the ratio of 3: 1 of blue: pink

but the observed number of offspring -

Blue color petals = 192

pink color petals = 63

Total = 192 + 63 = 255

Expected Number of offspring -

Blue color petals = 3 $\div$ 4 $\times$ 255 = 191.25

pink color petals = 1 $\div$ 4 $\times$ 134 = 63.75

So the number of observed offspring is close to the number of expected offspring, i.e. in the ratio of 3: 1.

Cross 3-

When we make a cross between the pink and white flower then in the F1 generation we get all the offspring having blue color petals- this is an example of complementation, where the two different organisms having different homozygous recessive characteristics are producing the same phenotype.

Cross 4-

When we cross the offspring of the F1 generation obtained from cross 3 , then in the F2 generation we get the ratio of blue : white: pink = 272: 121: 89

Total = 272 + 121 + 89 = 482

Thus the complementation observed in Cross 3.