Genetic drift widens the expected cline but narrows the expected cline width

article Genetic drift widens the expected cline but narrows the expected cline width published yes Jitka Polechova author 3BBFB084-F248-11E8-B48F-1D18A9856A870000-0003-0951-3112 Nicholas H Barton author 4880FE40-F248-11E8-B48F-1D18A9856A870000-0002-8548-5240 NiBa department Limits to selection in biology and in evolutionary computation project Random genetic drift shifts clines in space, alters their width, and distorts their shape. Such random fluctuations complicate inferences from cline width and position. Notably, the effect of genetic drift on the expected shape of the cline is opposite to the naive (but quite common) misinterpretation of classic results on the expected cline. While random drift on average broadens the overall cline in expected allele frequency, it narrows the width of any particular cline. The opposing effects arise because locally, drift drives alleles to fixation—but fluctuations in position widen the expected cline. The effect of genetic drift can be predicted from standardized variance in allele frequencies, averaged across the habitat: 〈F〉. A cline maintained by spatially varying selection (step change) is expected to be narrower by a factor of relative to the cline in the absence of drift. The expected cline is broader by the inverse of this factor. In a tension zone maintained by underdominance, the expected cline width is narrower by about 1 – 〈F〉relative to the width in the absence of drift. Individual clines can differ substantially from the expectation, and we give quantitative predictions for the variance in cline position and width. The predictions apply to clines in almost one-dimensional circumstances such as hybrid zones in rivers, deep valleys, or along a coast line and give a guide to what patterns to expect in two dimensions. Genetics Society of America2011 eng Genetics 00029472160001810.1534/genetics.111.129817 1891227 - 235 Polechova J, Barton NH. 2011. Genetic drift widens the expected cline but narrows the expected cline width. Genetics. 189(1), 227–235. Polechova, Jitka, and Nicholas H. Barton. “Genetic Drift Widens the Expected Cline but Narrows the Expected Cline Width.” Genetics, vol. 189, no. 1, Genetics Society of America, 2011, pp. 227–35, doi:<a href="https://doi.org/10.1534/genetics.111.129817">10.1534/genetics.111.129817</a>. J. Polechova and N. H. Barton, “Genetic drift widens the expected cline but narrows the expected cline width,” Genetics, vol. 189, no. 1. Genetics Society of America, pp. 227–235, 2011. Polechova J, Barton NH. Genetic drift widens the expected cline but narrows the expected cline width. Genetics. 2011;189(1):227-235. doi:<a href="https://doi.org/10.1534/genetics.111.129817">10.1534/genetics.111.129817</a> J. Polechova, N.H. Barton, Genetics 189 (2011) 227–235. Polechova, J., & Barton, N. H. (2011). Genetic drift widens the expected cline but narrows the expected cline width. Genetics. Genetics Society of America. <a href="https://doi.org/10.1534/genetics.111.129817">https://doi.org/10.1534/genetics.111.129817</a> Polechova, Jitka, and Nicholas H Barton. “Genetic Drift Widens the Expected Cline but Narrows the Expected Cline Width.” Genetics. Genetics Society of America, 2011. <a href="https://doi.org/10.1534/genetics.111.129817">https://doi.org/10.1534/genetics.111.129817</a>. 33942018-12-11T12:03:05Z2025-09-30T08:42:59Z