Lethal alleles
Encyclopedia
Allele
s that cause an organism to die only when present in homozygous condition are called lethal alleles. The gene
involved is considered an essential gene.
When Mendel's Laws were rediscovered, geneticist
s believed that mutation
s would only alter the appearance of a living organism. However, it was discovered that a mutant allele could cause death. When an essential gene is mutated, it can result in a lethal phenotype
. If the mutation is caused by a dominant lethal allele, the heterozygote for the allele will show the lethal phenotype, the homozygote dominant is impossible. If the mutation is caused by a recessive lethal allele, the homozygote for the allele will have the lethal phenotype.
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s that cause an organism to die only when present in homozygous condition are called lethal alleles. The gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
involved is considered an essential gene.
When Mendel's Laws were rediscovered, geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
s believed that mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s would only alter the appearance of a living organism. However, it was discovered that a mutant allele could cause death. When an essential gene is mutated, it can result in a lethal phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
. If the mutation is caused by a dominant lethal allele, the heterozygote for the allele will show the lethal phenotype, the homozygote dominant is impossible. If the mutation is caused by a recessive lethal allele, the homozygote for the allele will have the lethal phenotype.