If the expression of a trait requires only one copy of a gene (one allele), that trait is considered dominant. If the expression of a trait requires 2 copies of a gene (2 alleles), that trait is considered recessive. One exception is X-linked disorders.
Genetic variation can be caused by mutation. Hope this helped. ;)
ATP RNA DNA phospholipids
C.<span>trees going dormant in winter to survive unfavorable conditions</span>