Sunday, November 12, 2017

Genetic Detection of Immigrants

Multilocus genotypes.

Detecting immigrants from the analysis of multilocus genotypes: paper here.  An old paper; of course, methodology has gone past this since; nevertheless, it deserves to be noted, for the idea that looking at multilocus genotypes allows for distinguishing genetic types even when "bean bag genetics" differentiation is low.  The basic premise; emphasis added:

Immigration is an important force shaping the social structure, evolution, and genetics of populations. A statistical method is presented that uses multilocus genotypes to identify individuals who are immigrants, or have recent immigrant ancestry. The method is appropriate for use with allozymes, microsatellites, or restriction fragment length polymorphisms (RFLPs) and assumes linkage equilibrium among loci. Potential applications include studies of dispersal among natural populations of animals and plants, human evolutionary studies, and typing zoo animals of unknown origin (for use in captive breeding programs). The method is illustrated by analyzing RFLP genotypes in samples of humans from Australian, Japanese, New Guinean, and Senegalese populations. The test has power to detect immigrant ancestors, for these data, up to two generations in the past even though the overall differentiation of allele frequencies among populations is low.

Classical theory in population genetics has focused on the long term effects of immigration on allele frequency distributions in semi-isolated populations, concentrating on the stationary distribution resulting from a balance between forces of immigration, genetic drift, and mutation (1–4). Less theory exists addressing the effect of recent immigration among populations with low levels of genetic differentiation. A theory describing the effects of immigration on the genetic composition of individuals in populations that are not at genetic equilibrium is needed to interpret much of the data being generated using current genetic techniques. 
In this paper we consider the multilocus genotypes that result when individuals are immigrants, or have recent immigrant ancestry. We propose a test that allows recent immigrants to be identified on the basis of their multilocus genotypes; the test has considerable power for detecting immigrant individuals even when the overall level of genetic differentiation among populations is low. Molecular genetic techniques that allow multilocus genotypes to be described from single individuals are relatively new, and much of the information contained in these types of data is not fully exploited by estimators of long term gene flow that are currently available (5–7). We provide an example of an application of the method to restriction fragment length polymorphism (RFLP) genotypes from human populations; the method may also be applied to analyze multilocus allozyme and microsatellite data.

 At least three potentially misleading results may arise when applying the method considered here. First, the failure to reject the hypothesis that an individual was an immigrant, or descended from immigrants, may simply reflect the fact that the appropriate populations for comparison were not included in the analysis. Second, an individual might incorrectly appear to have originated in a particular population other than the one from which it was sampled. This might be due to similarities in allele frequencies, due to long-term gene flow, between that population and a third population from which the individual actually originated, but which was not included in the sample of populations. Third, the fact that many pairwise comparisons between populations are performed for each of a large number of individuals means that some individuals will appear to be immigrants purely by chance.

See this as well.  And also this.

In the late 1990s and early 2000s, there was some work going on in population genetics concerning multilocus genotypes.  A lot of good could have come from that if it was continued.  By an interesting coincidence, work on this subject essentially ended around the same time Der Movement and the HBDers went online talking about, and dissecting, population genetics studies.  It could be a coincidence, but given how most population geneticists are hysterical SJWs, maybe some of them decided not to investigate areas of their field that would focus attention on the great degree of actual ethnoracial differentiation that exists when genetic structure is taken into account.