Disease that causes phenylalaline to build up to toxic levels causing issues in the brain because the body cannot metabolize it properly. Happens when both diseased alleles of the gene are present, and can be fatal but easily treated by avoiding it in your diet
Variable expressivity
When a phenotype can be stronger or weaker in individuals with the same genotype
Incomplete penetrance
When a gene is not always expressed in the phenotype, like when some people with a disease causing allele never get the disease
Polygenic inheritance
When multiple genes affect one trait, so the more of a gene that codes for one variation, the stronger it is in the phenotype (i.e. many genes coding for height compound into a tall person)
Phenotypic plasticity
When one gene can be expressed in different ways depending on the conditions
