Question

The ratio of 9:7 is due to:

• A. Lethal genes
• B. Supplementary genes
• C. Epistatic genes
• D. Complementary genes

Answer 1

The correct option is D

Complementary genes

The correct option is D.

Explanation of the correct option:

1. Complementary genes are the pair of genes that work together to express a particular human phenotype.
2. For example- In the cross between white flowers of Lathyrus odoratus,a white flower (CCpp) is crossed with another white flower (ccPP).
3. The F1 generation has all purple flowers ( CcPp).
4. When a purple flower is self-fertilized it gives 9 purple flowers and 7 white flowers making the ratio 9:7:
5. Thus the non-mendelian complementary genes show a 9:7 phenotypic ratio.

Explanation of the incorrect options:

Option A:

1. A lethal gene is one that in some (such as homozygous) conditions may prevent the development or cause the death of an organism.
2. Lethal genes show a 2:1 phenotypic ratio.

Option B:

1. Supplementary genes are genes that both contribute to a single characteristic, where one gene can mask the effect of the other.
2. Supplementary genes show a 9:3:4.

Option C:

1. Epistatic gene is one that determines whether or not a trait will be expressed.
2. Epistatic genes have a 9:3:3:1 ratio.

Final answer: The ratio of 9:7 is due to complementary genes.