Before reaching the adulthood some individuals die because of the presence of gene in the appropriate genotype is

Before reaching adulthood some individuals die because of the presence of the gene in the appropriate genotype Lethal gene.
This gene causes death if both recessive alleles are possessed by the same individual.
They are usually a result of mutations in genes that are essential for growth or development. Lethal alleles may be recessive, dominant, or conditional depending on the gene or genes involved.
Recessive lethal alleles do not cause death in the heterozygous form because a certain threshold of protein output is maintained. In the homozygous form, the protein output does not meet the threshold, causing death.