allelic and genotypic frequencies - (Apr/27/2008 )

What is the point of studying both the genotype and allelic frequencies in SNP cancer studies? Why isn't either sufficient?

Thanks
SF

I know nothing about SNP cancer studies, but I'll assume there is nothing unique about them. If you know the genotype frequencies in a population, you then also know the allele frequencies. But not the other way around. An example. Alleles A and B each have a frequency of 0.5. This tells you nothing about what gentotypes are represented. Hardy-Weinberg predicts a 25-50-25 split of AA-AB-BB, but you don't know this. It might be 10-80-10 with a bit of balancing selection going on. You have to genotype individuals to know what the genotype frequencies are. But if you first do the genotyping and find 40-40-20 for AA-AB-BB, then you know the allele frequencies are 0.6 and 0.4 just by counting how many As there are and how many Bs there are.