Homosexuality

even if the 1 in 4 cannot reproduce and have no advantage that recessive gene can still be passed on by the 2 in 4 who are heterozygous. One such example is cystic fibrosis. Until 50 years back, persons who had the disease (which is a recessive disorder) would die before the age of 10-15, i.e. before they could reproduce. Yet this disease was still present due to the heterozygotes passing on this gene and due to de novo mutations in the gene.