In humans dominant trait is wavy(w) and dark hair(d) . recessive trait is straight(w) and red hair(d).a wavy dark haired male had a straight red haired mother. his father's genotype is

WWDD, WwDd, WWDd or WwDD

Explanation:

Given that wavy and dark hair is dominant over straight and red hair. A male with dark wavy hair has mother with recessive straight red hair so her genotype is definitely wwdd.

The son will get recessive alleles "w" and "d" from his mother. But he shows dominant phenotype which means that his father gave him the dominant alleles "W" and "D". Hence his father can have WWDD, WwDd, WWDd or WwDD genotype.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).