Evolutionary Genetics Benjamin A. Pierce GENETICS A Conceptual Approach FIFTH EDITION CHAPTER 26 Evolutionary Genetics © 2014 W. H. Freeman and Company

Some chimpanzees, like humans, have the ability to taste phenylthiocarbamide (PTC), whereas others cannot taste it.

26.1 Evolution Occurs Through Genetic Change Within Populations “Nothing in Biology makes sense except in the light of Evolution” Theodosius Dobzhansky

26.1 Organisms Evolve Through Genetic Change Taking Place Within Populations Biological Evolution: genetic change in a group of organisms Evolution as a two-step process Types of evolution Anagenesis: evolution taking place in a single group (a lineage) with the passage of time Cladogenesis: splitting of one lineage into two, new species arise

Figure 26.1 Anagenesis and cladogenesis are two different types of evolutionary change. Anagenesis is change within an evolutionary lineage; cladogenesis is the splitting of lineages (speciation).

26.2 Many Natural Populations Contain High Levels of Genetic Variation Genetic variation must be present for evolution to take place Molecular Variation Protein Variation DNA Sequence Variation

Figure 26.2 Early evolutionary geneticists were forced to rely on the phenotypic traits that had a simple genetic basis. Variation in the spotting patterns of the butterfly Panaxia dominula is an example.

26.2 Many Natural Populations Contain High Levels of Genetic Variation Molecular Variation Molecular data are genetic Molecular methods can be used with all organisms Molecular methods can be applied to a huge amount of genetic variation All organisms can be compared with the use of some molecular data Molecular data are quantifiable Molecular data often provide information about the process of evolution The database of molecular information is large and growing

26.2 Many Natural Populations Contain High Levels of Genetic Variation Protein Variation: analyze proteins in a population to identify genotype Measures of genetic variation proportion of polymorphic loci expected heterozygosity Explanation for protein variation neutral-mutation hypothesis: individuals with different molecular variants have equal fitness at realistic population size. Balance hypothesis: genetic variation in natural populations is maintained by selection that favors variation.

Figure 26.3 Molecular variation in proteins is revealed by electrophoresis. Tissue samples from Drosophila pseudoobscura were subjected to electrophoresis and stained for esterase. Esterases encoded by different alleles migrate different distances. Shown on the gel are homozygotes for three different alleles.

Concept Check 1 Which statement is true of the neutral-mutation hypothesis? All proteins are functionless. Natural selection plays no role in evolution. Most molecular variants are functionally equivalent. All of the above.

Concept Check 1 Which statement is true of the neutral-mutation hypothesis? All proteins are functionless. Natural selection plays no role in evolution. Most molecular variants are functionally equivalent. All of the above.

26.2 Many Natural Populations Contain High Levels of Genetic Variation DNA Sequence Variation: analyze genetic variation Restriction-site variation Microsatellite variation Variation detected by DNA sequencing

Figure 26.4 Microsatellite variation has been used to study the response of bighorn sheep to selective pressure on horn size due to trophy hunting. [Eyewire.]

Figure 26.5 Evolutionary tree showing the relationships of HIV isolates from a dentist, seven of his patients (A through G), and other HIV-positive persons from the same region (local controls, LC). The phylogeny is based on DNA sequences taken from the envelope gene of the virus. [After C. Ou et al., Molecular epidemiology of HIV transmission in a dental practice, Science 256:1167, 1992.]

26.3 New Species Arise Through the Evolution of Reproductive Isolation The Biological Species Concept (Ernst Mayer, 1942) A group of organisms whose members are capable of interbreeding with one another but are reproductively isolated from the members of other species.

26.3 New Species Arise Through the Evolution of Reproductive Isolation Reproductive Isolating Mechanisms Modes of Speciation Genetic Differentiation Associated with Speciation

26.3 New Species Arise Through the Evolution of Reproductive Isolation Reproductive Isolating Mechanisms Prezygotic reproductive isolating mechanisms Ecological Behavioral Temporal Mechanical Gametic Postzygotic reproductive isolating mechanisms Hybrid inviability Hybrid sterility Hybrid breakdown

26.3 New Species Arise Through the Evolution of Reproductive Isolation Speciation: process by which new species arise Allopatric speciation When a geographic barrier splits a population into two or more groups and prevents gene flow between the isolated groups Sympatric speciation arises in the absence of any geographic barrier to gene flow; reproductive isolation mechanisms evolve within a single interbreeding population. Speciation through polyploidy

Figure 26.6 Allopathic speciation is initiated by a geographic barrier to gene flow between two populations.

Figure 26.7 The Galápagos Islands are relatively young geologically and are volcanic in origin. The oldest islands are to the east. [Adapted from Philosophical Transactions at the Royal Society of London, Series B 351:756–772, 1996.]

Figure 26.8 Darwin’s finches consist of 14 species that evolved from a single ancestral species that migrated to the Galápagos Islands and underwent repeated allopatric speciation. [After B. R. Grant and P. R. Grant, Bioscience 53:965–975, 2003.]

Figure 26.9 The number of species of Darwin’s finches present at various times in the past corresponds with the number of islands in the Galápagos archipelago. [Data from P. R. Grant, B. R. Grant, and J. C. Deutsch, Speciation and hybridization in island birds, Philosophical Transactions of the Royal Society of London, Series B 351:765–772, 1996.]

Figure 26.10 Host races of the apple maggot fly, Rhagoletis pomenella, have evolved some reproductive isolation without any geographic barrier to gene flow.

Figure 26.11 Spartina anglica arose sympatrically through allopolyploidy.

26.3 New Species Arise Through the Evolution of Reproductive Isolation Genetic Differentiation Associated With Speciation How much genetic differentiation is required for reproductive isolation to take place?

26.4 The Evolutionary History of a Group of Organisms Can Be Reconstructed by Studying Changes in Homologous Characteristics Phylogeny The evolutionary relationships among a group of organisms are termed a phylogeny. Phylogenetic tree

Figure 26.12 A phylogenetic tree is a graphical representation of the evolutionary relations among a group of organisms.

Figure 26.13 A gene tree can be used to represent the evolutionary relationships among a group of genes. This gene tree is a rooted tree, in which PRL represents a prolactin gene; PRL1 and PRL2 are two different prolactin genes found in the same organism; and SOMA represents a somatropin gene, which is related to prolactin genes.

The Alignment of Homologous Sequences 26.4 The Evolutionary History of a Group of Organisms Can Be Reconstructed by Studying Changes in Homologous Characteristics The Alignment of Homologous Sequences Phylogenetic trees are often constructed from DNA sequence data The Construction of Phylogenetic Trees Distance approach Parsimony approach

Figure 26.14 There are three potential phylogenetic trees for humans, chimpanzees, and gorillas.

Concept Check 2 Which feature is found in a rooted phylogenetic tree but not in an unrooted tree? terminal nodes internal nodes a common ancestor to all other nodes branch lengths that represent the amount of evolutionary divergence between nodes

Concept Check 2 Which feature is found in a rooted phylogenetic tree but not in an unrooted tree? terminal nodes internal nodes a common ancestor to all other nodes branch lengths that represent the amount of evolutionary divergence between nodes

Rates of Molecular Evolution 26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level Rates of Molecular Evolution Rates of nucleotide substitution Nonsynonymous and synonymous rates of substitution Substitution rates for different parts of a gene

Figure 26. 15 Different parts of genes evolve at different rates Figure 26.15 Different parts of genes evolve at different rates. The highest rates of nucleotide substitution are in sequences that have the least effect on protein function.

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level The Molecular Clock The rate at which a protein evolves is roughly constant over time Therefore, the amount of molecular change that a protein has undergone can be used as a clock

Figure 26.17 The molecular clock is based on the assumption of a constant rate of change in protein or DNA sequence. Relation between the rate of amino acid substitution and time since divergence, based in part on amino acid sequences of alpha hemoglobin from the eight species shown in part b.The constant rate of evolution in protein and DNA sequences has been used as a molecular clock to date past evolutionary events.

Concept Check 3 In general, which types of sequences are expected to exhibit the slowest evolutionary change? synonymous changes in amino acid coding regions of exons nonsynonymous changes in amino acid coding regions of exons introns pseudogenes

Concept Check 3 In general, which types of sequences are expected to exhibit the slowest evolutionary change? synonymous changes in amino acid coding regions of exons nonsynonymous changes in amino acid coding regions of exons introns pseudogenes

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level Evolution through changes in gene regulation Genome Evolution Exon shuffling Gene duplication Multigene family concept

Figure 26.17 Sub-Saharan African populations of the fruit fly Drosophila melanogaster exhibit a positive association between pigmentation and elevation.

Figure 26.18 Human globin genes constitute a multigene family that has evolved through successive gene duplications.

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level Genome Evolution Whole-genome duplication Horizontal gene transfer