Linkage - Non-Independent Events

Locus one and two are located on the same chromosome and are linked with recombination fraction = r. A and B are linked in coupling phase.

Testcross AaBb x aabb.

If r < 0.5, then we do not realize a 1/4:1/4:1/4:1/4 ratio of the progeny.

This result is because the probability of the A and B alleles being in the same gamete is not the product of the probabilities of two independent events.

Example:

Coupling phase linkage between two loci with p = 0.2, testcross progeny.