Some traits, such as earlobe attachment, blood type, and the presence or absence of dimples, have limited variation throughout t
he 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
The correct answer would be "they are polygenic traits".
Polygenic traits are those which are controlled by at least two different genes.
As more than two genes are involved in controlling a single trait, so they show more variations as compared to the traits which are controlled by a single gene.
For example, height is controlled by at least three genes and thus six alleles are involved in regulating height.
Polygenic traits often show a bell-shaped curve in a population.
