Dihybrid cross

Gregor Mendel’s pea plant experiment on 2 traits: roundness (Rr) and yellowness (Yy), led to the discovery of a fundamental law of genetics called the Law of Independent Assortment. The ratio 9:3:3:1 is calculated by a Punnett grid.

P Generation

The experiment first crosses two homozygous parental organisms that differed in two traits. Homozygous and dominant for round (RR), yellow (YY) seeds with homozygous and recessive for wrinkled (rr), green (yy) seeds.

F1 Generation

The offspring of the homozygous RRYY seeds with homozygous rryy seeds cross, which is called the F1 generation, are all heterozygous plants with round, yellow seeds phenotype and the genotype YyRr.

Punett grid

It shows the genotypes two individuals can produce when crossed. Capital letters represent dominant alleles, and lower case letters recessive alleles. It shows how these alleles are passed on to offspring from parents.