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Effective Population Size A line graph shows the relationship between the effective mating population and the number of females present in the population. NF, the number of females, is shown on the X-axis. NE, the effective mating population, is shown on the vertical Y-axis. The graph exhibits a downward-opening parabola curve. The height of the line increases as NF increases from 0 to 500. In this half of the graph, less than half of the effective mating population is female. When NF reaches 500, exactly half of the effective mating population is female. In contrast, the height of the line decreases as NF increases from 500 to 1000, indicating that more than half of the effective mating population is female. Figure 4: The relationship between Ne and Nf in a population of 1000 mating individuals. © 2008 Nature Education All rights reserved. View Terms of Use Because most populations are large, it seems fair to ask whether genetic drift is really all that important. It's true that most populations are large, but they don't necessary act large. Thus, the rate of genetic drift is not really proportional to census population size (Nc). Rather, it's proportional to something more abstract — specifically, the effective population size (Ne). In an ideal population of sexually reproducing individuals , Ne will equal Nc. An “ideal“ population has the following characteristics, and most deviations will decrease the effective population size: There are equal numbers of males and females, all of whom are able to reproduce. All individuals are equally likely to produce offspring, and the number of offspring that each produces varies no more than expected by chance. Mating is random. The number of breeding individuals is constant from one generation to the next. Essentially, anything that increases the variance among individuals in reproductive success (above sampling variance) will reduce Ne (the size of an ideal population that experiences genetic drift at the rate of the population in question). For example, consider the effect of unequal numbers of mating males and females. In an ideal population, all males and all females would have an equal chance of mating. However, in situations in which one sex outnumbers the other, an individual's chance to mate is now affected by its sex, even if all individuals within each sex have an equal chance to mate. In this situation, effective population size can be predicted by the formula Ne = 4NmNf/(Nm Nf), where Nm is the number of males and Nf is the number of females. Figure 4 shows the relationship between Ne and Nf in a population of 1,000 mating individuals. In an ideal population, all individuals have an equal opportunity to pass on their genes. In real life, however, this is rarely the case, and Ne is particularly sensitive to unequal numbers of males and females in the population. #dnaMolecule #molecularBiology #GeneStructure #gene #phenotype #mRNA #protein #codons #Promoter #rnaSplicing #gregorMendel #Haploid #Heterozygous #genomes #Genetics101 #transcription #GeneticsLecture #geneExpression #AllelicFrequencies #genes #genome #geneticDrift #BloodType #eukaryotes #explain #prokaryotes #Cancer #alleles #nucleicAcids #mitosis #genetics #tRNA #Isochromosome #dominant #NikolaysGeneticsLessons
