A homozygous tall plant (T) bearing red coloured (R) flowers is crossed with a homozygous dwarf (t) plant bearing white (r) flowers:
Mention the possible combinations of the gametes that can be obtained from the F1 hybrid plant.
Topic: Gametes of a dihybrid
Answer
Each TtRr plant produces FOUR kinds of gamete: TR — tall and red Tr — tall and white tR — dwarf and red tr — dwarf and white
THE RULE: each gamete receives ONE allele from each pair. With two pairs (T/t and R/r), the number of possible combinations is 2 × 2 = FOUR.
Write them SYSTEMATICALLY so none is missed: take T with R, then T with r, then t with R, then t with r.
THE REASON there are four rather than two is MENDEL’S LAW OF INDEPENDENT ASSORTMENT — the T/t pair separates independently of the R/r pair, so T can go with either R or r.
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.