Question

Assume height in a plant is controlled by three genes (A, B and C) and each additive allele contributes equally. The base height is 20 cm and maximum possible height is 38 cm. The height of a plant with genotype AAbbCc will be:

• A. 32 cm
• B. 29 cm
• C. 19 cm
• D. 25.4 cm

Hint:

Calculate the value of a single dominant allele first: (Max - Base) Total Alleles.

Answer 1

The Correct Option is B

Step 1: Concept
Polygenic inheritance involving additive alleles means each dominant allele adds a specific amount to the base phenotype.

Step 2: Meaning
Base height (0 dominant alleles) = 20 cm. Max height (6 dominant alleles: AABBCC) = 38 cm.

Step 3: Analysis
Total increase = $38 - 20 = 18$ cm. Contribution per dominant allele = $18 / 6 = 3$ cm. Genotype AAbbCc has 3 dominant alleles (A, A, C). Height = Base + (3 alleles $\times$ 3 cm/allele) = $20 + 9 = 29$ cm.

Step 4: Conclusion
A plant with 3 additive alleles will be 29 cm tall. Final Answer: (B)