The "big five" assumptions are the ones listed in the main text. However, the basic formulation of Hardy-Weinberg equilibrium also relies on a few other assumptions;

Allele and genotype frequencies don't differ between males and females. That is, the basic form of Hardy-Weinberg does not cover sex-linked genes.

so, is there a modified formula?

• What "main text" are you referring to? Mar 31, 2018 at 19:25
• Also, exactly what is your question (modified formula of what?)? Is it on how to calculate genotypic frequencies in the presence of sex-linkage, or on how sex-linkage affects the HW-equilibrium? Mar 31, 2018 at 19:33

Solving Hardy-Weinberg problems

First of all, you might want to have a look at the post

and eventually at

After reading the first post, you should be able to answer your question yourself. I encourage you to try it before reading what follows.

I will make an example. Let's consider a case where males are XY and females XX (like in mammals for example). Let A and B be two alleles of a bi-allelic present on the X chromosome. The frequency of these two alleles in the entire population are $$p$$ and $$q$$. Let's assume the locus is present on the X chromosome. We will assume that the allele frequency do not differ between males and females.

In males, there are two possible genotypes. A and B. Their frequency among males are noted $$f_{m,A}$$ and $$f_{m,B}$$ are

$$f_{m,A} = p$$

$$f_{m,B} = q$$

In females, there are three possible genotypes. AA, AB (or BA) and BB. Their frequency among females are noted $$f_{f,AA}$$, $$f_{f,AB}$$ and $$f_{f,BB}$$ and are

$$f_{f,AA} = p^2$$ $$f_{f,AB} = 2pq$$ $$f_{f,BB} = q^2$$

If the sex ratio (the ratio of the number of males over the number of females) is $$r$$, then the genotypes frequencies in the overall population are the ones from above multiplied by $$r$$ and $$1-r$$ for males and females, respectively.