3. Three linked loci A, B, C (each with two alleles as in Question 2) in a random mating population have the gametic frequencies as shown below. Calculate the linkage disequilibium D/Dmax between each pair of loci. Explain why the results seem paradoxical. [based on Hartl 1.15 try on your own before checking the answer, and show your calculations for D and Dmax]

Gamete ABC ABc AbC Abc aBC aBc abC abc Frequency 0.25 0 0.25 0 0 0.25 0 0.25

in a large population, allele frequencies do not change from one generation to the next if there is random mating, and one generation of random mating is enough to create the Hardy-Weinberg genotype frequencies at loci even if they did not start off that way.

However, Linkage Disequilibrium, as measured by D, becomes smaller in each subsequent generation by a factor of (1-r), where r = recombination.

Suppose you sample a human population and find the following number of individuals that have these allelic combinations at two protein-coding genes (or loci) known to be on the same chromosome. Lets call these locus A and locus B, with two possible alleles A and a at locus A, and two possible alleles B and b at locus B:

Gamete, or chromosome, haplotype: AB, Ab, aB, ab Number in sample: 3, 27, 37, 33