10. When two independent pure lines of pea with white flowers are crossed, the F1 progeny has purple flowers. The progeny obtained on selfing shows both pruple and white flower in a ratio of 9:7. The following conclusions were made
A. Two different genes are involved, mutation in which lead to formation of white flower.
B. These two genes show independent assortment
C. This is an example of complementary gene action
D. The is an example of duplicate genes
Which of the following conclusions are correct?
(1) A and C only (2) A and D only
(3) A, B and D (4) A, B and C
Explanation of the 9:7 Flower Color Ratio in Pea Plants
The observation of a 9:7 phenotypic ratio of purple to white flowers in the F2 progeny of crossing two pure white flower pea lines indicates an example of complementary gene action. This involves two different genes, both essential for producing the purple flower pigment. Mutation in any one of these two genes leads to white flowers, hence only those plants with at least one dominant allele in both genes exhibit purple flowers. The genes assort independently, but both must be functionally present, resulting in the classic 9:7 ratio.
Analysis of the Given Conclusions
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A. Two different genes are involved, mutation in which lead to formation of white flower: Correct; both genes contribute to pigment production, and mutations cause white flowers.
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B. These two genes show independent assortment: Correct; the genes are non-allelic and segregate independently in Mendelian fashion.
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C. This is an example of complementary gene action: Correct; both dominant alleles are required for purple coloration.
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D. This is an example of duplicate genes: Incorrect; duplicate genes typically produce a 15:1 ratio, where either gene alone can produce the dominant phenotype. Here, both are necessary.
Summary Table of Genetic Concepts for This Case
| Conclusion | Correct or Not | Explanation |
|---|---|---|
| A | Correct | Two genes mutated to cause white flowers |
| B | Correct | Independent assortment of two non-allelic genes |
| C | Correct | Complementary gene action requiring both dominant alleles |
| D | Incorrect | Duplicate genes produce different ratios, not 9:7 |
The correct answer is (4) A, B, and C because the phenotypic ratio and flower color inheritance reflect two independently assorting genes working complementarily to produce purple flowers, and mutations in either cause white flowers.
