What causes some genetic conditions to be rarer than others?
In: 3
The incidence of those genes in the general population and whether the disease is a recessive or dominant trait. The incidence in the population is obviously determined by just how the genetic disease harms you. If it’s extremely deadly and his at an early age then it’s probably going to be very rare due to natural selection. Conversely if it doesn’t really affect you until old age then there’s a lot less of an evolutionary pressure to eliminate it from the gene pool.
Well, there are a lot of factors.
* Dynamics of mutation: some mutations can happen more easily than others. (For example, the mutation that causes Huntington’s Disease happens in a stretch of repetitive DNA that is supposed to read `CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG CAG`. Because of the repetition, the copying enzyme tends to lose its place, making this an unusually unstable part of the genome.)
* Dynamics of evolution: some genetic conditions are going to interfere with reproduction more than others. (For example, since Tay-Sachs Disease causes death in early childhood, sufferers of it will never reproduce. On the other hand, since it’s a recessive condition rather than a dominant one, carriers of it *can* reproduce. Compare with a dominant condition, or with one that has milder and/or later-onset symptoms.)
* Random chance: if a carrier of a genetic condition happened to have a lot of descendants at some point in history, the condition could end up being more common than we would otherwise expect. (For example, Hemophilia B famously spread through the European royalty. It’s easy for rich and powerful men to have a lot of children, even if those men are sickly.)
Latest Answers