In Mendel's experiments with garden pea, round seed shape (RR) was dominant over wrinkled seeds (rr), yellow cotyledon (YY) was dominant over green cotyledon (yy). What are the expected phenotypes in the F2 generation of the cross RRYY × rryy?
- Round seeds with yellow cotyledons, and wrinkled seeds with yellow cotyledons
- Only wrinkled seeds with green cotyledons
- Only wrinkled seeds with yellow cotyledons
- Only round seeds with green cotyledons
Answer
(1) Round seeds with yellow cotyledons, and wrinkled seeds with yellow cotyledons
Solution
As per NCERT, RRYY rryy gives F1 = RrYy (round, yellow).
When the F1 is selfed (RrYy × RrYy), the two characters assort independently, so the F2 shows the ratio 9 : 3 : 3 : 1, i.e. 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.
Hence round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons are both expected in the F2 (along with round green and wrinkled green), while options (2), (3) and (4) are wrong because no single phenotype appears 'only'.
Answer: (1)