Finding specific genotype occurrences given allele frequency So let's say I have a tetraploid species and I have 4 possible alleles for a particular locus. I have found that I can have 35 total possible genotypes and I know the allele frequencies for each of the 4 alleles, that I will randomly set as $$F_a = 0.2, F_b = 0.3, F_c = 0.4, F_d=0.1$$ for the sake of the example. However, I am having a hard time wrapping my mind around how to calculate the number of occurrences of a particular genotype, $abc$, in a population of 1000 people. I understand the allele frequencies, for instance, in the population of 1000 people, given all 1000 observed genotypes, 40% of them had allele $c$. But these are individual values and I have no information on how likely they are to be linked. (I am supposed to assume HW principle holds, but not sure how this helps). How do I calculate the number of occurrences of the genotype $abc$ in the population?

Under Hardy-Weinberg conditions, the frequency of the genotype `abcd` (in this particular order) is simply $F_a \cdot F_b \cdot F_c \cdot F_d = 0.24\%$.

If we don't consider the order, then we must ultiply the previous probability by 24. There are indeed 24 (=4*3*2*1) ways you can get this particular combination. The probability of `abcd` in any particular order is therefore $24 \cdot F_a \cdot F_b \cdot F_c \cdot F_d = 5.76\%$.

You might want to have a look at the post Solving Hardy Weinberg problems