hard · Enhanced ACT science
A yellow, round-seeded pea plant (from a true-breeding YYRR line) was crossed with a green, wrinkled-seeded plant (true-breeding yyrr). The yellow, round F1 (YyRr) was then self-pollinated to produce 300 F2 seeds. If the two genes assort independently, the classic 9:3:3:1 ratio predicts about 169 yellow-round, 56 yellow-wrinkled, 56 green-round, and 19 green-wrinkled seeds. The actual F2 counts were:
| Phenotype | Observed count |
| :--- | :--- |
| Yellow, round | 204 |
| Yellow, wrinkled | 18 |
| Green, round | 16 |
| Green, wrinkled | 62 |
Compared with the 9:3:3:1 prediction, these results best support the conclusion that:
- the two genes assort completely independently, as Mendel predicted.
- the genes are linked, since parental types dominate over recombinants.
- the shape allele is fully epistatic to the color allele in offspring.
- a lethal recessive combination is eliminating specific genotype combinations entirely.
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