Relationship coefficient
The relationship coefficient ( R for short ; see also coefficient : "Beizahl, Vorzahl") calculates the closeness of the biological relationship between two living beings based on the probability that they have inherited the same (randomly selected) genetic information from each other or from a common ancestor . The genetic makeup of identical twins or clones (copies) is completely identical because they are genetically identical individuals - consequently they have a coefficient of 1.00 = 100%.
The kinship coefficient makes a mathematical prediction regarding the state of a gene ( allele ) at any location on a chromosome ( locus ) in two individuals with a common ancestry , sometimes incorrectly referred to in the specialist literature as the degree of kinship . The calculation was developed in 1947 by the French biomathematist Gustave Malécot .
Because a parent passes on 50% of their genetic material to their direct descendants , there is a relationship coefficient of 0.5 (1/2) between them and their biological child : there is a 50% probability that a child's individual genetic information will match his own. Full siblings have the same coefficient to each other, while half siblings and grandparents and grandchildren only have a relationship coefficient of 0.25 (1/4). The more generations back the last common ancestor, the lower the genetic match in his descendants ( see below for relative preference and the inbreeding coefficient).
| relationship | Relationship Coefficient (R) |
|---|---|
| Identical twins or two clones | 1/1 = 1.00 = 100% match |
| Parent ↔ child | 1/2 = 0.50 = 50% ... |
| Brother ↔ sister | 1/2 = 0.50 = 50% ... |
| Half brother ↔ half sister | 1/4 = 0.25 = 25% ... |
| Grandparent ↔ grandchild | 1/4 = 0.25 = 25% ... |
| Uncle, aunt ↔ nephew, niece | 1/4 = 0.25 = 25% ... |
| Cousin ↔ cousin (1st degree) | 1/8 = 0.125 = 12.5% ... |
| Cousin ↔ cousin (1st degree, 1 generation postponed) |
1/16 = 0.0625 = 6.25% ... |
| Cousin ↔ cousin 2nd degree | 1/32 = 0.03125 = 3.125% ... |
| 3rd cousin ↔ cousin | 1/128 = 0.0078125 = 0.78125% ... |
Cousins and cousins The distance between cousins (1st degree: normal) and 2nd degree cousins shifts by 2 degrees of relationship: In the direct line of the ancestors, it goes back 1 generation to their common ancestors, the great-grandparents (or only to one great-grandparent), and then in the two branches of the family (side lines) again 1 before the current generation (see also direct and lateral relationship ). Accordingly, the values of the "distant" cousins are only a quarter of those of the 1st degree. In the case of 3rd degree cousins (2 back, 2 forwards) the values drop well below the statistical average and are negligible. These low values represent the small genetic “remnants” of the original great-great-grandparents who gave birth to two children who in turn established the two different sidelines of the third-degree cousins.
Relatives preference The level of the kinship coefficient also plays a role in explaining selfless acts ( altruism ) in humans and animals or in social succession (see relatives selection , for example the avunculate of the mother's brother or uncle , or the milk relationship through joint breastfeeding). In sociobiology and psychobiology , the level of the kinship coefficient of individuals allows corresponding predictions to be made about their behavior, which ensures that their own gene is more successful in reproduction .
Inbreeding If two relatively close blood relatives common progeny attest , there are changes in the relationship coefficients of these progeny . The so-called inbreeding coefficient of the descendants of two individuals is almost half their relationship coefficient . For persons whose parents are blood relatives (1st degree) (R = 0.125), the inbreeding coefficient of their children is 6.25 percent (see inbreeding in humans , human genetic counseling , relatives and loss of ancestors ).
See also
- Genetic genealogy (determination of the degree of relationship based on DNA analyzes)
- Ancestral loss coefficient (individual ancestors appear in several ancestral positions at the same time)
literature
- Jan Murken et al.: Relationship coefficient R. In: Humangenetik. 7th, completely revised edition. Thieme Verlag, Stuttgart 2006, ISBN 9783131392978 , pp. 251-252 ( page views in the Google book search).
- Gustave Malécot , Louis Florimond Blaringhem : Les Mathématiques de l'hérédité. Masson, Paris 1947 (French).
Web links
- Joachim Jakob: Eusociality. In: Biology Learning Programs. Kronberg-Gymnasium Aschaffenburg, accessed on March 29, 2018 (part of the “Cooperators” learning program ).
Individual evidence
- ^ Benedikt Hatz: Investigations of the genetic diversity within the genus Hordeum with molecular marker techniques. Utz, Munich 1997, ISBN 3-89675-191-3 , p. 12 (doctoral thesis at the Technical University of Munich): "Relationship coefficients according to ( MALÉCOT , 1969) [...] The coefficient that quantifies the relationship between two individuals describes the probability that two randomly selected alleles are identical in both individuals due to their common descent (KEMPTHORNE, 1969). "
- ^ Gustave Malécot , Louis Florimond Blaringhem : Les Mathématiques de l'hérédité. Masson, Paris 1947 (French).
- ↑ Jan Murken et al.: Inbreeding and kinship coefficient for different kinship relationships. In: Human Genetics. 7th, completely revised edition. Thieme Verlag, Stuttgart 2006, ISBN 9783131392978 , p. 252: table (there also the exact formulas; side view in the Google book search).