10.2 Inheritance

Dihybrid crosses

Taking an example studied by Mendel of two unlinked genes. The gene that controls the colour of the peas pods which has 2 alleles.

The dominant allele R (green) and the recessive r (yellow)

and the gene that controls the shape of the pod the dominant allele Y (wrinkled) and the recessive y (smooth).

As these alleles are found on different chromosomes they will be independently assorted. The genes are unlinked. This will mean that 4 possible gametes can be produced during meiosis.Each will have a probabilty of ΒΌ.image

This is a common phenotypic ratio 9:3:3:1. This comes from parents which are heterozygous for both alleles and the genes are unlinked. image

9 Green wrinkled: 3 Green smooth: 3 Yellow wrinkled:1 Yellow smooth

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