Fraternal twins , also known as `` non-identical twins '' or dizygotic twins : Two separate ova are fertilized , which each becomes a zygote . Fraternal or dizygotic ( DZ ) twins ( also referred to as `` non-identical twins '' , `` dissimilar twins '' , `` biovular twins '' , and , in cases of females , occasionally sororal twins ) usually occur when two fertilized eggs are implanted in the uterus wall at the same time . When two eggs are independently fertilized by two different sperm cells , fraternal twins result .