Some traits, such as earlobe attachment, blood type, and the presence or absence of dimples, have limited variation throughout the human population because they are controlled by a single gene. other traits, such as skin color and human height, are widely variable throughout the human population because. a. they can not be affected by environmental factors b. they are controlled by only one gene c. they are controlled by more than one gene d. they are not controlled by genes in any way

The right option is; C. They are controlled by more than one gene  

Traits such as skin color, human height and eye colour are known as polygenic traits. These traits have wide variation throughout the human population and are controlled by two or more genes. For example the human height is controlled by at least three genes with six alleles. The quantities of the genes are usually large but often have a little effect.

the diploid number of chromosomes is sometimes represented by the symbol 2n. for the fruit fly, the diploid number is 8, which can be written as 2n = 8, where n represents twice the number of chromosomes in a sperm or egg cell.