Answer: D. traits
Explanation: Every trait is controlled by at least a pair of gene, one inherited from the mother while the other inherited from the father . An allele is a variant form of a gene that controls a trait. Every gene that controls a trait is made up of at least two alleles. An allele can be dominant or recessive for example, T is a dominant allele for tall height while t is a recessive allele for short height. If a woman with a genotype of Tt crosses with a man with a genotype of Tt, a child that inherited a (T) allele from the mother and a (T) allele from the father and have a genotype (TT) will have a different trait from his sibling that inherited a (t) allele from the mother and a (t) allele from the father and have a genotype of (tt). The child who has a genotype of TT will be tall while his sibling with genotype of tt will be short. This is because each of them inherited different set of allele from the same parents.