How Did I Get FCS
In order for you to have this condition both of your parents must be carriers of the faulty gene. If you have inherited one faulty gene from each parent you will be born with the condition.
This means that patients with FCS who go on to have children will pass down the carrier status to their children. Depending on their partners – whether they are carriers, patients or have no faulty gene – their children will have a varying risk of having the condition or being carriers themselves.
This can be illustrated using A and Z, A being the faulty gene and Z being the functional gene.
Patients have two faulty genes AA. Carriers have one faulty, one functional AZ. FCS-free people have two functional genes ZZ.
FCS plus FCS-Free
For a patient who has a child with someone with no FCS status their child will be a carrier having one faulty gene from their FCS parent and one functional gene from their non-FCS parent. All options mean the child is a carrier. (So AA plus ZZ leads to AZ, AZ, AZ, AZ).
Carrier plus Carrier (illustrated)
For two carriers of the condition they have a 25% chance of having a child with the condition, a 50% chance of their child being a carrier and a 25% chance of the child being FCS-free. (AZ plus AZ leads to AA, AZ, ZA, ZZ.)
In the very unlikely event that two people with FCS have a child, each child will definitely have the condition. (AA plus AA leads to AA. AA, AA, AA.)