How is it possible that a lethal recessive gene can be maintained in a population? Give an example.

Genes are the stretch of DNA that code for a specific protein and thereby regulate a genetic trait. Genes are present on chromosomes and have two or more alternative forms called alleles. 

The presence of alleles of some genes in the homozygous state might cause the death of the organism. These genes which are fatal and cause death of the person or an organism are said to be lethal genes. Most of the lethal genes are recessive, that is, recessive homozygous genotypes are lethal. However, the dominant alleles of some genes are also lethal.

Example: Huntington’s chorea is caused by a dominant allele that causes nervous and motor degeneration in the affected person and leads to death.