QQuestion
With the help of a table show the genotypes bearing genotypic ratio two (2) produced in F₂ generation as a result of a cross between a pea plant having pure round yellow coloured seed (RRYY) and another pea plant having pure wrinkled green coloured seed (rryy).
✓Answer
In this dihybrid cross RRYY × rryy, all F₁ plants are RrYy.
Selfing of F₁ (RrYy × RrYy) produces F₂ with 9:3:3:1 phenotypic ratio and a 1:2:2:4:1:2:1:2:1 genotypic ratio.
The genotypes which occur with frequency “2” in F₂ are shown below:
| Genotype | How it appears in F₂ |
|---|---|
| RR Yy | From YR × RY and Yr × RY gamete combinations (2 out of 16) |
| Rr YY | From YR × yR and YR × yR combinations (2 out of 16) |
| Rr yy | From yr × Yr and yr × Yr combinations (2 out of 16) |
| rr Yy | From yR × yr and yR × yr combinations (2 out of 16) |
| rr Yy | Thus each of these genotypes has genotypic ratio 2 in F₂. |
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