A recessive genetic disease occurs when both copies of a particular gene have pathogenic variants. If you have one copy of a gene with a variant and one normal copy of that same gene, you are considered a "carrier" for that recessive genetic disease even though you are not affected by that disease.

In order for carriers to pass on a recessive gene, both partners would have to be carriers of the same genetic disease.

A dominant genetic disease occurs when one of the two copies of a particular gene has a pathogenic variant. Only one of the copies of the gene needs to have a pathogenic variant in order for an individual to be affected by a dominant genetic disease (recessive diseases require both copies to have variants). If either you or your partner have a dominant genetic disease, you run a 50% risk of having a child affected by that genetic disease.

The X and Y chromosomes (often called the sex chromosomes) determine whether a baby is male or female. Males have one X and one Y, while females have two X chromosomes. Some disorders are caused by variants or alterations of the X chromosome. Generally, if a woman has a pathogenic variant on one of the genes located on an X chromosome, she is considered a carrier — and has a 50% chance of passing that variant onto her children. If she passes on the variant on to a male child, that child can be affected with the condition. Affected males will not pass the variant onto their sons, but daughters of affected males will be carriers of the variant. Female carriers rarely develop symptoms of the condition but their daughters have a 50% chance of being carriers.