Question

A plant of $F_1$ generation with genotype "AABbCC". On selfing of this plant what is the phenotypic ratio in $F_2$ -generation : -

• A. 3 : 1
• B. 1 :1
• C. 9 : 3 : 3 : 1
• D. 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

Answer 1

The Correct Option is A

The given question asks about the phenotypic ratio observed in the F_2 generation of a plant with the genotype "AABbCC". Let's solve this problem step-by-step.

Step 1: Understand the Genotype

The genotype of the F_1 generation plant is "AABbCC". This indicates the following alleles:

• AA: Homozygous dominant for the first trait.
• Bb: Heterozygous for the second trait.
• CC: Homozygous dominant for the third trait.

Step 2: Selfing and Gamete Formation

During self-pollination, the plant can produce gametes as follows:

• The "AA" allele will produce only "A" (since it is homozygous).
• The "Bb" allele can produce either "B" or "b".
• The "CC" allele will produce only "C" (since it is homozygous).

Hence, the possible gametes are: A (from AA), B or b (from Bb), and C (from CC), giving combinations of: ABC and AbC.

Step 3: Determine the F_2 Generation

Since the heterozygous pair "Bb" can result in either "B" or "b", we focus on the F_2 offspring ratio for this trait:

• The combination "BB" will exhibit the dominant phenotype.
• The combination "Bb" and "bB" will also exhibit the dominant phenotype (since "B" is dominant).
• The combination "bb" will exhibit the recessive phenotype.

This means that for the trait governed by "B", the phenotypic ratio is 3 (dominant): 1 (recessive).

Step 4: Conclusion

The phenotypic ratio for the F_2 generation of this plant, considering the effect of the heterozygous "Bb" pair, is 3 : 1, since both "AA" and "CC" are homozygous and only "Bb" contributes to a differing phenotypic outcome based on allele combination.