Recessive lethal

Recessive Lethal

Recessive lethal (/rɪˈsɛsɪv ˈliːθəl/) is a term used in Genetics to describe a genetic mutation that results in the death of an organism when present in two copies, but has no effect when present in only one copy.

Etymology

The term "recessive lethal" is derived from the words "recessive", which refers to a trait that is not expressed when a dominant trait is present, and "lethal", which means deadly or fatal.

Definition

A recessive lethal allele is a variant of a gene that is lethal to the organism when it is homozygous, i.e., when two copies of the same allele are present. This means that the organism will not survive if it inherits two copies of the recessive lethal allele, one from each parent. However, if the organism inherits only one copy of the recessive lethal allele and one copy of a normal allele (heterozygous), it will survive, as the normal allele is dominant and masks the effect of the recessive lethal allele.

Related Terms

Homozygous: An organism that has two identical alleles for a trait.
Heterozygous: An organism that has two different alleles for a trait.
Dominant allele: An allele that is expressed in the phenotype, even if only one copy is present.
Genotype: The genetic makeup of an organism.
Phenotype: The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences.

Examples

Recessive lethal alleles are found in many species, including humans. For example, the genetic disorder Cystic Fibrosis is caused by a recessive lethal allele. Individuals who are heterozygous for the cystic fibrosis allele are carriers of the disease but do not show symptoms themselves.