The closely related fields of population genetics and quantitative genetics both focus on the genetic basis of phenotypic variation among the individuals in a population. Population genetics traditionally deals with frequencies of alleles and genotypes, whereas quantitative genetics concentrates on the ways that individual variation in genotype and environment contribute to variance in phenotype. The articles in this topic room represent a blend of both subjects.
The topic room begins with an explanation of Hardy-Weinberg equilibrium, a simple model that predicts unchanging genotype frequencies in a randomly mating, infinitely large population in the absence of selection, migration, or new mutation. A pair of articles by Kent Holsinger then introduces two important analytical approaches (maximum likelihood and Bayesian analysis) as employed in the context of Hardy-Weinberg equilibrium.
Next, Norman Johnson discusses the important debate regarding adaptive landscapes, a concept first proposed by Sewall Wright. A related article explains the concepts of genetic drift and effective population size.
Moving to quantitative genetics, Diane Byers introduces components of phenotypic variance, while Naomi Wray and Peter Visscher explain heritability, which is mathematically defined as the proportion of phenotypic variance attributable to additive genetic variance. (Although a trait may show phenotypic variation among individuals, it must be heritable to respond to artificial or natural selection.) Derek Roff then explains threshold traits, or traits with discrete character states that are better described by quantitative genetics than by simple Mendelian inheritance. After that, Cecelia Miles and Marta Wayne discuss quantitative trait loci in model organisms: what they are, how they are mapped, and why we care.
Finally, Leslie Pray has also contributed three "why we care" articles to this room. In her contributions, Pray describes the relevance of population genetics to conservation (see her article on the bearded vulture), to efforts to better understand human genomic epidemiology (see her article on the HuGE project), and to the use of quantitative trait loci in agriculture (see her article on building a better tomato).
Image: © 2007 Nature Publishing Group. Poelwijk, F. J. et al. Empirical fitness landscapes reveal accessible evolutionary paths. Nature 445, 383–386 doi:10.1038/nature05451. All rights reserved.
