Lethal factor

A lethal factor or lethal error is an allele of a gene that is fatal in a homozygous form before the affected individual is sexually mature . In animal breeding , such an allele in its heterozygous form can have desirable effects on the phenotype for breeding purposes (e.g. taillessness in Manx cats or feather bonnets in certain canary breeds ), so that the incentive can exist to use corresponding alleles despite their negative effects on the animals actively promote.

In Germany , lethal factors in small animals such as dogs, cats, rabbits and birds are banned from breeding in the report on Section 11b of the Animal Welfare Act ( torture breeding ).

Manifestation of the effect

Homozygous dwarf from the mating of two dwarf rabbits (not viable, death usually a few days after birth)

The lethal effect of a lethal factor in homozygous individuals can occur in different stages of development, depending on the factor:

• In the germ cells (not viable or fertile)
• During embryonic development
• During fetal development
• After giving birth

Similar alleles

Dominant lethal factors

Hutchinson-Gilford progeria as an example of a dominant lethal factor that only shows effects after birth

Dominant lethal factors are alleles which lead to death in a heterozygous form. Due to this fact, they cannot stay in a population permanently, but arise sporadically through spontaneous mutations . Progeria is an example of a dominant lethal factor .

Semi-lethal factors

A semiletal factor or error , similar to a lethal factor, is fatal in homozygous form; however, the lethality is less than 100 percent of the homozygous individuals. In such cases, one can therefore speak of a lethal factor with incomplete penetrance .

Lethality Equivalent

One speaks of a lethality equivalent in the case of a single mutation or a sum of mutations of different alleles, which in the case of homozygosity lead to the death of the affected individual with a hundred percent probability. Such a summation of various factors is useful in the case of polygenic inheritance and simultaneous consideration of various semiletal factors.

literature

• Ekkehard Wiesner, Siegfried Willer: Genetic advice in veterinary practice. Gustav Fischer, Jena 1993, ISBN 3-334-60420-9 .