In some autosomal recessive conditions in humans, the homozygous recessive genotype results in death before reproductive age - VCE - SSCE Biology - Question 23 - 2004 - Paper 1

In populations exhibiting autosomal recessive conditions, heterozygotes often possess a fitness advantage, especially in environments where carriers may be more resistant to certain diseases. This phenomenon, known as heterozygote advantage, allows the allele for the recessive trait to persist in the population, despite the disadvantage of homozygous recessive individuals. This advantage ensures that the recessive alleles are maintained within the gene pool, despite the reduced reproductive rates of those homozygous for the recessive allele.