Abstract
Extensive Monte Carlo simulations are conducted of spatial distributions of two-locus genotypes in large, continuous populations under isolation by distance models. The results show that substantial patches of double homozygotes are present in the spatial structures, even when loci are unlinked. The stochastic spread of identical two-locus genotypes largely outpowers the tendency for recombination to decouple patterns for separate loci. A spatial patch is a large area containing mostly one double homozygous genotype in a highly contiguous constellation. This patch structure is reflected in high positive spatial autocorrelations and large excesses of pairs, or joins, of identical double homozygotes at short-to-intermediate distances of spatial separation. Although spatial patches of double homozygotes are the dominant spatial feature, and the major contributors to overall high levels of autocorrelations among two-locus genotypes, other substantial features include areas of concentrations of identical genotypes heterozygous at only one locus. One implication of the patch structure is the presence of high levels of linkage disequilibrium, caused by isolation by distance even for unlinked loci, at some spatial scales; yet the disequilibrium in the large total populations is near 0. Thus linkage disequilibrium produced by isolation by distance is highly dependent on spatial scale. Another implication is that high degrees of spatial structuring and autocorrelations are produced for genetic variation controlling quantitative traits, at least when the number of loci is relatively small, under a wide range of situations, even if the trait is selectively neutral. The significance of the results to field studies is also examined.
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Selected References
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- Christiansen F. B., Feldman M. W. Subdivided populations: a review of the one- and two-locus deterministic theory. Theor Popul Biol. 1975 Feb;7(1):13–38. doi: 10.1016/0040-5809(75)90003-9. [DOI] [PubMed] [Google Scholar]
- Epperson B. K., Allard R. W. Spatial autocorrelation analysis of the distribution of genotypes within populations of lodgepole pine. Genetics. 1989 Feb;121(2):369–377. doi: 10.1093/genetics/121.2.369. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Epperson B. K. Spatial autocorrelation of genotypes under directional selection. Genetics. 1990 Mar;124(3):757–771. doi: 10.1093/genetics/124.3.757. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lewontin R. C., Krakauer J. Distribution of gene frequency as a test of the theory of the selective neutrality of polymorphisms. Genetics. 1973 May;74(1):175–195. doi: 10.1093/genetics/74.1.175. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mitton J. B., Koehn R. K. Population genetics of marine pelecypods. 3. Epistasis between functionally related isoenzymes of Mytilus edulis. Genetics. 1973 Mar;73(3):487–496. doi: 10.1093/genetics/73.3.487. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nagylaki T. Geographical variation in a quantitative character. Genetics. 1994 Jan;136(1):361–381. doi: 10.1093/genetics/136.1.361. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rogers A. R., Harpending H. C. Population structure and quantitative characters. Genetics. 1983 Dec;105(4):985–1002. doi: 10.1093/genetics/105.4.985. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sokal R. R. Genetic, geographic, and linguistic distances in Europe. Proc Natl Acad Sci U S A. 1988 Mar;85(5):1722–1726. doi: 10.1073/pnas.85.5.1722. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sokal R. R., Jacquez G. M., Wooten M. C. Spatial autocorrelation analysis of migration and selection. Genetics. 1989 Apr;121(4):845–855. doi: 10.1093/genetics/121.4.845. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sokal R. R., Wartenberg D. E. A Test of Spatial Autocorrelation Analysis Using an Isolation-by-Distance Model. Genetics. 1983 Sep;105(1):219–237. doi: 10.1093/genetics/105.1.219. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weir B. S. Inferences about linkage disequilibrium. Biometrics. 1979 Mar;35(1):235–254. [PubMed] [Google Scholar]
- Wright S. Isolation by Distance. Genetics. 1943 Mar;28(2):114–138. doi: 10.1093/genetics/28.2.114. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zhivotovsky L. A., Feldman M. W. Heterogeneous selection in subdivided populations. J Math Biol. 1993;31(7):747–759. doi: 10.1007/BF00160423. [DOI] [PubMed] [Google Scholar]