How can a change in genotype affect the phenotype?

The genome in which a genotype is found can affect the expression of that genotype, and the environment can affect the phenotype. Genes can also be pleitropic when they affect more than one trait. The single base pair mutation that lead to sickle cell anemia is a classic example.

population

Explanation: An organism's genotype is the set of genes that it carries. ... However, since an organism's genotype generally affects its phenotype, the phenotypes that make up the population are also likely to change. For example, differences in the genotypes can produce different phenotypes.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

if you look up in the top right corner you'll see your current profile picture, click than click "view profile" you'll be able to change it there.