Using the following settings, press "Generate Pedigree" (NOT "Generate Random Pedigree") three to six times, and notice the frequency of affected sons and daughters in the F1 to F4 progeny.

Settings:

Mode of inheritance - X-linked recessive

Parental generation -

Male - Nonmutant

Female - Heterozygous

Matings between relatives - disallow

Progeny in first generation - 4

Show carriers - turn on

Why aren't there any affected females in the F1 generation under these conditions?