Question

A dihybrid cross is done on pea plants with the character colour (P vs. p) and pollen shape (round L vs long l). The resulting F2 generation has the phenotypic ratios; 6:2:2:6 for PL:Pl:pL:pl. Explain this finding.

Answer 1

A dihybrid cross is created on pea plants where the dihybrids separate two genes independent of each other. Consider two traits for pea: – Character Color: P  and p (P vs. p) – Pollen Shape: L (round) and Long l (round L vs long l) Initially, genetically identical line is created for both the PPLL and ppll traits. Growing dihybrid plant produces 4 gamete forms of equal frequency. – Adult PpLl.  Four gamete types are formed : PL, Pl, pL, pl. The resulting F2 generation has the phenotypic ratios; 6:2:2:6 for PL:Pl:pL:pl.

From the above results, we can see that,

• A dihybrid cross follows the law of independent assortment and there is an individual who is heterozygous at two PpLl genes where the F2 is located for parental or recombinant types and new varieties which are not present in the parents.
• F2 generation constituted both parental types and recombinant types.
• F2 revealed four distinct phenotypes: the round and coluored traits appeared opposite to each other.
• Gene alleles assort independently, and can also occur in the offspring for any variation.
• The overall phenotypic ratios; 6:2:2:6 .