"Explain what accounts for such a large amount of genetic variation within the human population?"

humans are adapted to a wide range of environments, and genetic variation leads to phenotypic variation

Explanation:

It has been shown that the average genetic variation between human individuals is about 0.1% (i.e., one base pair out of every 1,0000 are different between any two individuals). This value seems low, but it is huge when we consider that the current estimate for the world population is 7,800,000,000 people. The phenotype is the result of the interaction between genotype and environment. Genetic variation is the raw material that enables some individuals to adapt to different environments. As species, humans have a high genetic diversity in order to develop a wide range of phenotypes well adapted to different environmental conditions.

a chair, a bed, and a toothbrush

explanation:

i was told this before by a teacher, so yeah

"do a testcross with a homozygous recessive plant."