So, here’s something I don’t understand. I have sickle-cell disease and I’m told it’s a genetic condition, but neither my dad nor my mom have it.

Well, genetic inheritance is a bit more complex than most people imagine it to be. There are different “modes” of inheritance. Sickle-cell disease, for example, is transmitted from parents to child in an “autosomal recessive” fashion.

An auto-whatnow? How are cars involved?

No, “autosomal”. It means the mutation that causes the disease is located on one of the 22 human chromosomes that are not sex chromosomes. These 22 chromosomes are known as “autosomes”.

Oh, I see. So you’re saying that I got this mutation from my dad and my mom, though, right?

Yes.

So how come they don’t have the disease?

The most likely explanation is that both your parents are “carriers”. You see, we each have two copies of every chromosome: one copy…