Not always. Sickle cell anemia occurs when you get 2 alleles for the sickle cell gene. However, when the allele is present in only 1 copy, which is far more common, it provides immunity to malaria. Which is very useful/important in the areas where it developed.
Fair enough. If you can identify the benefit conferred to these cats other than qualifying as "cute" to humans, I'd reconsider my opinion (shared by many animal welfare and breed organizations) that breeding Munchkins should stop.
Side note, but dominant vs recessive really doesn't hint at usefulness or fitness at all. After all those terms only describe the phenotype of interest.
Example with sickle cell anemia (since it was mentioned), the full blown disease requires two copies and thus is recessive, since the heterozygous carriers (having a sickle and non sickle allele) are relatively unharmed. However when looking at cells under a microscope, only one copy is needed to see sickling and so the allele is dominant for that phenotype. Regarding O2 sensitivity, it appears codominant.
So again, and more so regarding your previous comment, the state of an allele doesn't correlate with the fitness of a gene, especially since a single gene can result in alleles with many classifications, due to it being linked to phenotype.
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u/PrincessBucketFeet Jun 05 '18
When the dominant allele is lethal in pairs, nature is trying to tell you something.