Tuesday, February 14, 2012
Traits vs. Genes
If you get half your genes from your mum and the other half from your dad why don't you have half your mums feature's and half of your dad's?
There is something wonderful about this simple question, and all of genetics could be used to answer it. Three points seem to be worth making.
1) Dominance. If a specific trait is conferred by a dominant allele and both parents are heterozygous, then their child can lack a trait that they share.
2) Features are not genes. Some traits (features) are affected by many genes, and many genes affect multiple traits.
3) Many traits are complex. Geneticists distinguish between simple (Mendelian) traits and complex traits. Traits can show the following sorts of genetic complexity:
epistasis (where the effect of one gene depends on other genes)
incomplete penetrance (where a specific genotype doesn't always have the usual effect)
polygenic inheritance (where multiple genes affect the trait)
genetic heterogeneity (where different genes cause the same trait in different families or populations)
phenocopy (when traits that often have a genetic basis arise without a genetic basis)
Explaining all of this in detail would require a complete course in genetics!