![]() ![]() ![]() Gene flow tends to be positively correlated with genetic diversity and Ne, and negatively with the rate of genetic drift within populations and the extent of genetic differentiation among populationsĬonnected populations Isolated populations (gene flow) (no gene flow)Ĭrocodile (Crocodylus moreletii) in Belize, Central America. Table 4.9 Some of the ways in which gene flow (and lack thereof) can influence population genetics. The importance of gene flow to the genetic diversity - and hence the survival - of threatened or endangered populations was illustrated by a study of Morelet's Even low levels of immigration can introduce new genotypes and increase the effective size, and hence genetic diversity, of local populations (see Box 4.4). Since gene flow reduces the rate of genetic drift, it stands to reason that, all else being equal, isolated populations will have a lower Ne, a higher rate of drift, and lower genetic variation compared with populations that receive immigrants (Table 4.9). In fact, theory predicts that Nem values as low as one per generation may be sufficient to prevent the differentiation of populations by genetic drift (Wright, 1931). Of inbreeding within a local population relative to the collective population, and reflects the probability that two alleles drawn at random from within a population are identical by descent, an FST value of 0.2 means that the local population is only 20 per cent more inbred than the collective population, even though gene flow is still very low. The FST values are reduced rapidly even with low levels of gene flow ![]() Since FST is a measure of the degreeįigure 4.11 Comparison of the genetic differentiation between populations (FST) and the accompanying indirect estimates of gene flow (Nem), based on the relationship FST = 1/(4Nem+1). If one migrant moves between a pair of populations every generation (Nem = 1), then FST = 0.20. With only one migrant every fourth generation (Nem = 0.25), Fst will be reduced to 0.5. From this equation we can see that although populations are maximally divergent when Nem = 0 and FST =1, even small increases in gene flow (Nem) will markedly reduce population differentiation (Fst) (Figure 4.11). Earlier in this chapter we learned that when populations are in equilibrium, FSt = l/(4Nem + 1). Consider once more the relationship between gene flow and population differentiation (FST). However, very little gene flow is necessary to reduce the rate of genetic drift and thereby prevent substantial population subdivision. They add, though, that there are still unanswered questions about the population history of the Ryukyu Islands, such as the origin of the Paleolithic populations, which they say could be answered through additional ancient and modern genomic analysis.In the absence of gene flow, conspecific populations will generally diverge from one another as a result of genetic drift. "e identified a genetic cline among Ryukyu Islanders that was shaped primarily by genetic drift that occurred in a subpopulation of the Miyako Islands and by interregional migrations," the researchers write. From this, they noted a genetic difference between Okinawa and Miyako islanders, though they find that this difference is likely due to genetic drift rather than any differences in gene flow to the two island groups from the main islands of Japan or from Taiwan. ![]() In the Journal of Human Genetics, researchers from the University of the Ryukyus examine the genetic population structure of Ryuku Islanders using whole-genome sequencing data from Okinawa and Miyako islanders alongside publicly available East and Southeast Asian datasets. The Ryuku Islands form the southernmost part of the Japanese Archipelago and themselves can be grouped into the Amami Islands, the Okinawa Islands, the Miyako Islands, and the Yaeyama Islands. Genetic drift may have shaped the differences in demographic history observed between Ryukyu Islander populations, a new study suggests.
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