POPULATION GENETICS & EVOLUTION -Overview DR. KOFI OWUSU-DAAKU 27th January 2016 POP GEN & EVOL LECTURE 1

Clown, Fool, or Simply Well Adapted? The blue-footed booby has many specialized characteristics that are very functional in water but less useful on land Such evolutionary adaptations are inherited traits that enhance an organism's ability to survive and reproduce in its particular environment Evolution is the changes in organisms over time 27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-7a Webbing No webbing 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

DARWIN'S THEORY OF EVOLUTION A sea voyage helped Darwin frame his theory of evolution Pre-Darwinian ideas about the origin of species Early Greek philosophers: Simpler life forms preceded more complex ones Aristotle: Species are fixed and do not evolve; had a great impact on Western thinking Judeo-Christian biblical view: All species were individually designed by a divine creator 27th January 2016 POP GEN & EVOL LECTURE 1

PRE-DARWINIAN IDEAS In the century prior to Darwin, only a few scientists questioned the belief that species are fixed Buffon: The study of fossils suggested that Earth is older than 6,000 years, and fossil forms might be early versions of modern forms Lamarck: Fossils are related to modern forms because life evolves; acquired characteristics are inherited 27th January 2016 POP GEN & EVOL LECTURE 1

DARWIN’S VOYAGE Charles Darwin made a round-the-world sea voyage as a naturalist on HMS Beagle in the 1830s Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands Darwin's experiences during the voyage helped him frame his ideas about evolution Lyell's Principles of Geology led him to realize that still-operating natural forces gradually change Earth 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-1b 27th January 2016 POP GEN & EVOL LECTURE 1 Great Britain Europe Asia North America ATLANTIC OCEAN PACIFIC OCEAN Africa PACIFIC OCEAN Equator The Galápagos Islands South America PACIFIC OCEAN Pinta Genovesa Australia Marchena Equator Santiago Andes Cape of Good Hope Daphne Islands Fernandina Pinzón Tasmania Isabela Santa Cruz Cape Horn New Zealand Santa Fe San Cristobal Tierra del Fuego 40 km Florenza Española 40 miles 27th January 2016 POP GEN & EVOL LECTURE 1

DARWINS AFTER VOYAGE IDEAS After his return, Darwin began to document his observations and his new theory of evolution Alfred Wallace conceived a theory almost identical to Darwin's; both works were presented to the scientific community Darwin's On the Origin of Species by Means of Natural Selection was published in 1859 27th January 2016 POP GEN & EVOL LECTURE 1

"Descent with modification" summarizes Darwin's view of life All organisms are related through descent from a remote common ancestor Descendants spread into diverse habitats over millions of years and acquired adaptations to their environments The history of life resembles a tree with multiple branchings from a common trunk Species that are closely related share characteristics 27th January 2016 POP GEN & EVOL LECTURE 1

Darwin proposed natural selection as the mechanism of evolution The essence of Darwin's theory of natural selection is differential success in reproduction Organisms produce more offspring than the environment can support Organisms vary in many characteristics that can be inherited Excessive numbers of organisms lead to a struggle for survival 27th January 2016 POP GEN & EVOL LECTURE 1

Natural selection is supported by evidence from artificial selection Individuals whose characteristics are best adapted to their environment are more likely to survive and reproduce The unequal ability of individuals to survive and reproduce leads to a gradual change in the characteristics of a population over generations Natural selection is supported by evidence from artificial selection 27th January 2016 POP GEN & EVOL LECTURE 1

SELECTION IN ACTION -ARTIFICIAL 27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-2c African wild dog Coyote Wolf Fox Jackal Thousands to millions of years of natural selection Ancestral canine 27th January 2016 POP GEN & EVOL LECTURE 1

FOSSILS AS EVIDENCE OF EVOLUTION The study of fossils provides strong evidence for evolution Fossils are the hard parts of organisms that remain after organic materials decay Rarely, an entire organism is fossilized The fossil record strongly supports the theory of evolution Changes in sea level and drying and refilling of lakes over time result in rock strata that trap organisms 27th January 2016 POP GEN & EVOL LECTURE 1

Fossils appear in an ordered array within layers of sedimentary rocks The fossil record reveals that organisms have evolved in a historical sequence Many fossils link early extinct species with species living today 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

OTHER EVIDENCE FOR EVOLUTION A mass of other evidence reinforces the evolutionary view of life Biogeography The geographic distribution of species suggested to Darwin that organisms evolve from common ancestors Isolated organisms resemble each other more than organisms in similar but distant places 27th January 2016 POP GEN & EVOL LECTURE 1

Comparative anatomy Homologous structures are features that often have different functions but are structurally similar because of common ancestry Vestigial structures are remnants of structures that served important functions in an organism's ancestors 27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-4a Human Cat Whale Bat 27th January 2016 POP GEN & EVOL LECTURE 1

Comparative embryology Common embryonic structures in all vertebrates are evidence for common descent 27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-4b Pharyngeal pouches Post-anal tail Chick embryo Human embryo 27th January 2016 POP GEN & EVOL LECTURE 1

Molecular biology Comparisons of DNA and amino acid sequences between different organisms reveal evolutionary relationships Molecular biology provides strong evidence that all life forms are related 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

CONNECTION Scientists can observe natural selection in action Examples of evolutionary adaptation observed over a short time Different camouflage adaptations in different environments Development of pesticide resistance in insects 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

conferring resistance to pesticide LE 13-5b Chromosome with gene conferring resistance to pesticide Pesticide application Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Survivor 27th January 2016 POP GEN & EVOL LECTURE 1

Natural selection is contingent on time and place Examples of evolutionary adaptation reveal three key points about natural selection Natural selection is more of an editing process than a creative mechanism Natural selection is contingent on time and place Significant evolutionary change can occur in a short time 27th January 2016 POP GEN & EVOL LECTURE 1

POPULATION GENETICS AND THE MODERN SYNTHESIS 13.6 Populations are the units of evolution Population A group of individuals of the same species living in the same place at the same time May be isolated from other groups or concentrated The smallest unit that can evolve 27th January 2016 POP GEN & EVOL LECTURE 1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

27th January 2016 POP GEN & EVOL LECTURE 1

Connects population genetics with other sciences Combines Darwin's and Mendel's ideas in studying how populations change genetically over time The modern synthesis Connects population genetics with other sciences Focuses on population as the unit of evolution and central role of natural selection 27th January 2016 POP GEN & EVOL LECTURE 1

Studying evolution at the population level Evolution: change in the prevalence of certain heritable characteristics in a population over a span of generations Gene pool: the total collection of genes in a population at any one time Microevolution: a change in the relative frequencies of alleles in a gene pool Species: a group of populations capable of interbreeding and producing fertile offspring 27th January 2016 POP GEN & EVOL LECTURE 1

The gene pool of a nonevolving population remains constant over the generations In a nonevolving population, the shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population In Hardy-Weinberg equilibrium, the frequency of each allele in the gene pool will remain constant unless acted upon by other agents 27th January 2016 POP GEN & EVOL LECTURE 1

The population is very large The population is isolated For a population to be in Hardy-Weinberg equilibrium, it must satisfy five main conditions The population is very large The population is isolated Mutations do not alter the gene pool Mating is random All individuals are equal in reproductive success 27th January 2016 POP GEN & EVOL LECTURE 1

The Hardy-Weinberg conditions are rarely met in nature We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Hardy-Weinberg equilibrium provides a basis for understanding how populations evolve 27th January 2016 POP GEN & EVOL LECTURE 1

CONNECTION The Hardy-Weinberg equation is useful in public health science Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population Example: phenylketonuria (PKU) 27th January 2016 POP GEN & EVOL LECTURE 1

OTHER FACTORS POWERING EVOLUTION In addition to natural selection, genetic drift and gene flow can contribute to evolution Genetic drift: change in the gene pool of a population due to chance Can alter allele frequencies in a population The smaller the population, the greater the impact Bottleneck effect: an event that drastically reduces population size Founder effect: colonization of a new location by a small number of individuals 27th January 2016 POP GEN & EVOL LECTURE 1

Original population Bottlenecking event Surviving population LE 13-9a Original population Bottlenecking event Surviving population 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

Gene flow: the movement of individuals or gametes between populations Can alter allele frequencies in a population Tends to reduce differences between populations Natural selection Best-adapted individuals have the most reproductive success Results in accumulation of traits that adapt a population to its environment 27th January 2016 POP GEN & EVOL LECTURE 1

CONNECTION Endangered species often have reduced variation Loss of genetic variability due to bottlenecking may reduce a population's ability to adapt to environmental change Particularly threatening to endangered species such as the cheetah 27th January 2016 POP GEN & EVOL LECTURE 1

VARIATION AND NATURAL SELECTION Variation is extensive in most populations Individual variation exists in all sexually reproducing populations Heritable variation results from a combination of genotype and environmental influences Polymorphism: two or more forms of phenotypic characteristics Geographic variation: variation of an inherited characteristic from place to place May occur along a geographic continuum (a cline) 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

Mutation and sexual recombination generate variation Mutations-changes in the nucleotide sequence of DNA-can create new alleles Only mutations in cells that produce gametes can affect a population's gene pool A mutation may rarely improve adaptation to the environment and thus contribute to evolution Sexual recombination generates variation by shuffling alleles during meiosis 27th January 2016 POP GEN & EVOL LECTURE 1

A1 A1 A2 A3 Parents  Meiosis A1 A2 A3 Gametes LE 13-12a 27th January 2016 POP GEN & EVOL LECTURE 1

A1 A2 A3 A1 A2 A1 A3 Gametes Fertilization Offspring, with new LE 13-12b A1 A2 A3 Gametes Fertilization A1 A2 A1 A3 Offspring, with new combinations of alleles and 27th January 2016 POP GEN & EVOL LECTURE 1

CONNECTION The evolution of antibiotic resistance in bacteria is a serious public health concern Natural selection has led to the evolution of antibiotic-resistant bacteria Overuse and misuse of antibiotics has contributed to the proliferation of antibiotic-resistant strains Example: tuberculosis 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

Diploidy and balancing selection preserve variation Diploidy (two sets of chromosomes) helps to prevent populations from becoming genetically uniform Recessive alleles are "hidden" from natural selection and remain in the population 27th January 2016 POP GEN & EVOL LECTURE 1

Balanced polymorphism may result from Balancing selection allows two or more phenotypic forms in a population Balanced polymorphism may result from Heterozygote advantage; example: sickle-cell disease Frequency-dependent selection Neutral variation provides no apparent advantage or disadvantage Example: fingerprints 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

The perpetuation of genes defines evolutionary fitness Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation Survival of genes depends on production of fertile offspring Selection indirectly adapts a population to its environment by acting on phenotype 27th January 2016 POP GEN & EVOL LECTURE 1

Natural selection can alter variation in a population in three ways Stabilizing selection: favors intermediate phenotypes Directional selection: acts against individuals at one of the phenotypic extremes Disruptive selection: favors individuals at both extremes of the phenotypic range 27th January 2016 POP GEN & EVOL LECTURE 1

LE 13-16 27th January 2016 POP GEN & EVOL LECTURE 1 Original population Frequency of individuals Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Disruptive selection 27th January 2016 POP GEN & EVOL LECTURE 1

Sexual selection may produce sexual dimorphism Sexual dimorphism The distinction in appearance between males and females of a species Sexual selection The determining of "who mates with whom" Leads to the evolution of secondary sexual characteristics that may give individuals an advantage in mating 27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

27th January 2016 POP GEN & EVOL LECTURE 1

Natural selection cannot fashion perfect organisms There are at least four reasons why natural selection cannot produce perfection Organisms are limited by historical constraints Adaptations are often compromises Chance and natural selection interact Selection can only edit existing variations 27th January 2016 POP GEN & EVOL LECTURE 1