Genetics are forgotten

Genetics! Genetics are just completely thrown out of the window in omegaverses and it always bothers me. Girls have XX chromosomes and boys have XY chromosomes. In lesbian couples, they cannot produce a male child. They have a 100% chance of a girl. In gay couples, there is a 25% chance of a girl, 50% chance of a boy, and 25% chance of an other/not/miscarriage? None of this is ever brought up! Where do they get these extra chromosomes to pass down for equal chances of the sexes? What about the a/b/o genders? How do those genetics work? I understand you are more likely to have an alpha or omega born to an alpha and omega parent, but what about the nuisances?