A pea plant which is homozygous for green pods which are inflated [GGII] is crossed with a homozygous plant for yellow pods which are constricted [ggii]. Answer the following questions:
Write the possible combinations of the gametes that can be obtained if two F1 hybrid plants are crossed.
Topic: Gametes of a dihybrid
Answer
Each GgIi plant produces FOUR kinds of gamete: GI, Gi, gI and gi
THE RULE: each gamete receives ONE allele from each pair. With two pairs (G/g and I/i), the number of possible combinations is 2 × 2 = FOUR.
Write them SYSTEMATICALLY so none is missed: take G with I, then G with i, then g with I, then g with i.
THE REASON there are four rather than two is MENDEL’S LAW OF INDEPENDENT ASSORTMENT — the G/g pair separates independently of the I/i pair, so G can go with either I or i.
Since each parent makes 4 kinds of gamete, the Punnett square has 4 × 4 = 16 boxes — which is where the numbers 9, 3, 3 and 1 come from.