Penetrance (genetics)

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In genetics , penetrance is understood to be the percentage probability with which a certain genotype leads to the development of the associated phenotype .

Complete and incomplete penetrance

A distinction is made between complete penetrance , in which there is always the expression or manifestation of the characteristic, and incomplete penetrance , in which the characteristics of the associated phenotype are not manifested in every case despite the existing genotype. The background to an incomplete penetrance (<100%) can be modifying genes , environmental influences or even chance.

Concordance and Discordance

If the penetrance is incomplete, the probability of manifestation of a feature can be calculated. The concordance figure for identical twins (EZ) is an auxiliary variable . Concordance means that the same characteristics appear phenotypically in EZ, discordance, if this is not the case, see also → twin research .

Penetrance and Expressiveness

Penetrance is a categorical characteristic, i.e. it only relates to the question of whether a phenotype belonging to the genotype is present or absent. The degree to which a penetrant allele is expressed as a feature in the phenotype is called expressivity in genetics .

Practical meaning

The penetrance of an allele influences the risk of disease for children of carriers of a hereditary condition .

evaluation

The designation of an inheritance with incomplete penetrance does not allow a statement to be made about which mechanisms are responsible for the expression or non-expression of the characteristic. The assumption of a simple Mendelian inheritance is often not justified, especially in cases where the penetrance falls below 50 percent. In such cases, the alternative hypothesis of a multifactorial inheritance must be considered. In addition, the inheritance can often be described more precisely with the help of heritability .

Examples

  • Neurofibromatosis , practically 100% penetrance
  • BRCA1 gene-dependent breast cancers (female), clinically about 8.5% penetrance.

Individual evidence

  1. ^ Gordon Allen : The meaning of concordance and discordance in estimation of penetrance and gene frequency. In: American Journal of Human Genetics . Volume 4, Number 3, September 1952, pp. 155-172, PMID 12985556 , PMC 1716426 (free full text).
  2. ↑ Friedrich Vogel : Textbook of general human genetics . Springer, Heidelberg 1961; Page 371 f.

literature

  • Jan Murken, Hartwig Clewe (Ed.): Human Genetics . Ferdinand Enke Verlag Stuttgart 1996, 6th edition. ISBN 3-432-88176-2