4
Types of Natural Selection and Tests
of Selection
David Enard
Abstract
Natural selection leaves distinct signals at loci in the genome that have experienced deleterious or advantageous mutations during their evolution. This chapter
provides an overview of the main signatures left by natural selection both at
the level of genetic variation within populations and at the level of differences
between species. The chapter also details a number of classic summary statistics
that exploit these signals to detect and quantify natural selection and the rationale
behind these statistics. As such, it offers a basic introduction.
4.1
Types of Selection and Their Effect on Linked Neutral Sites
4.1.1 Types of Selection
Different types of natural selection are distinguished based on the dynamics of
the selected alleles. There are three broad categories: positive directional selection,
balancing selection, and purifying selection.
Alleles under positive directional selection are advantageous alleles (here advantageous means higher reproductive success) where individuals carrying the allele
have a reproductive advantage. In the case of directional selection, assuming the
mutation becomes established in the population, the greater selective advantage
quickly drives the frequency of advantageous alleles from close to zero when they
first appear to 100% after a number of generations.
D. Enard ()
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
e-mail: denard@email.arizona.edu
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. E. Lohmueller, R. Nielsen (eds.), Human Population Genomics,
https://doi.org/10.1007/978-3-030-61646-5_4
69
Types of Natural Selection and Tests
of Selection
David Enard
Abstract
Natural selection leaves distinct signals at loci in the genome that have experienced deleterious or advantageous mutations during their evolution. This chapter
provides an overview of the main signatures left by natural selection both at
the level of genetic variation within populations and at the level of differences
between species. The chapter also details a number of classic summary statistics
that exploit these signals to detect and quantify natural selection and the rationale
behind these statistics. As such, it offers a basic introduction.
4.1
Types of Selection and Their Effect on Linked Neutral Sites
4.1.1 Types of Selection
Different types of natural selection are distinguished based on the dynamics of
the selected alleles. There are three broad categories: positive directional selection,
balancing selection, and purifying selection.
Alleles under positive directional selection are advantageous alleles (here advantageous means higher reproductive success) where individuals carrying the allele
have a reproductive advantage. In the case of directional selection, assuming the
mutation becomes established in the population, the greater selective advantage
quickly drives the frequency of advantageous alleles from close to zero when they
first appear to 100% after a number of generations.
D. Enard ()
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
e-mail: denard@email.arizona.edu
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
K. E. Lohmueller, R. Nielsen (eds.), Human Population Genomics,
https://doi.org/10.1007/978-3-030-61646-5_4
69