Evolution of Populations Chapter 11

11-1: Genes and Variation Population: group of individuals in the same species that interbreed; share a common gene pool Gene Pool: all of the alleles of all the individuals in a population

11-1: Genes and Variation Allele Frequency: proportion of one allele, compared with all the alleles for that trait, in the gene pool; given as a decimal or a percentage ◦ Evolution occurs when there is a change in the allele frequency of a population

11-1: Genes and Variation Where does genetic variation come from? ◦ Mutations: change in DNA  Occur during replication or due to chemicals, radiation, etc.  Don’t always change the phenotype ◦ Gene Shuffling/Recombination  Mostly occurs during meiosis (independent assortment, crossing-over)

11-2: Natural Selection in Populations Natural Selection acts on organisms that survive and reproduce, NOT the genes

11-2: Natural Selection in Populations Single Gene Traits: one gene controls the trait Polygenic Traits: more than one gene controls the trait; this produces a range of phenotypes

11-2: Natural Selection in Populations Normal Distribution: graph of numerical data that forms a bell-shaped curve and is symmetrical; typical for a polygenic trait ◦ Natural selection leads to changes in allele frequency, which can shift the curve  Remember: changes in allele frequency = evolution!

11-2: Natural Selection in Populations Stabilizing Selection: favors the average phenotype; the curve narrows

11-2: Natural Selection in Populations Directional Selection: one extreme form is favored (one end OR the other)

11-2: Natural Selection in Populations Disruptive Selection: both extremes are favored and the intermediate forms are eliminated

11-3: Other Mechanisms of Evolution Gene Flow: movement of alleles from one population to another ◦ Causes allele frequency to increase or decrease by chance ◦ Occurs often in fungi or plants who have seeds, spores, etc. that are easy for dispersal

11-3: Other Mechanisms of Evolution Genetic Drift: the random change in allele frequency in a population ◦ Causes a loss of genetic diversity ◦ More prevalent in smaller populations (easier for change to have an affect)

11-3: Other Mechanisms of Evolution Types of Genetic Drift: ◦ Bottleneck Effect – results from an event that drastically reduces the size of a population  Greatly reduces genetic variation

11-3: Other Mechanisms of Evolution Types of Genetic Drift: ◦ Founder Effect – occurs after a small number of individuals colonize a new area

11-3: Other Mechanisms of Evolution

Sexual Selection: traits that increase the ability of individuals to attract or acquire mates appear with increasing frequency in a population ◦ Types: Competition between males for female attention; Physical traits attract females

11-4: Hardy-Weinberg Equilibrium If no change takes place, the population doesn’t evolve and genetic equilibrium has been reached. Hardy-Weinberg Equilibrium: condition in which a population’s allele frequencies for a given trait do not change

11-4: Hardy-Weinberg Equilibrium Requirements for Hardy-Weinberg ◦ Very large populations  So genetic drift doesn’t have much effect ◦ No emigration or immigration  Gene pool must be kept separate ◦ No mutations  Would cause allele frequency to change ◦ Random mating  Atypical because some traits are favored over others ◦ No natural selection  Equal opportunity for survival and reproduction of all genotypes

11-4: Hardy-Weinberg Equilibrium Populations rarely meet all of the Hardy- Weinberg conditions, and the idea is more often used to compare real-life models to predicted data. Hardy-Weinberg Equation used to predict genotype frequencies in populations

11-4: Hardy-Weinberg Equilibrium p 2 + 2pq + q 2 = 1 and p + q = 1 p = frequency of the dominant allele q = frequency of the recessive allele p 2 = % of homozygous dominant individuals q 2 = % of homozygous recessive individuals 2pq = % of heterozygous individuals

11-4: Hardy-Weinberg Equilibrium In a population of 1000 fish, 640 have forked tail fins and 360 have smooth tail fins. Tail fin shape is determined by two alleles: forked is dominant over smooth. Using that, calculate the following: ◦ The frequency of the "aa" genotype. ◦ The frequency of the "a" allele. ◦ The frequency of the "A" allele. ◦ The frequencies of the genotypes "AA" and "Aa." ◦ The frequencies of the two possible phenotypes if "A" is completely dominant over "a."

11-5: Speciation through Isolation Formation of a new species: speciation Reproductive Isolation: a particular set of populations can no longer interbreed to produce fertile offspring. ◦ Physical separation ◦ Offspring don’t survive and reproduce

11-5: Speciation through Isolation Behavioral Isolation: isolation caused by differences in courtship or mating behaviors ◦ EX: fireflies Geographic Isolation: physical barriers can divide a population into two or more groups ◦ EX: rivers, mountains, etc. Temporal Isolation: groups reproduce at different times of day or year ◦ EX: common in plants

11-5: Speciation through Isolation results from which include produced by which result in Reproductive Isolation Isolating mechanisms Behavioral isolationTemporal isolation Geographic isolation Behavioral differencesDifferent mating times Physical separation Independently evolving populations Formation of new species

Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of time. Major Themes: ◦ extinction ◦ adaptive radiation ◦ convergent evolution ◦ coevolution ◦ punctuated equilibrium ◦ changes in developmental genes 11-6: Patterns of Evolution

Extinction ◦ More than 99% of all species that have ever lived are now extinct. ◦ Currently, the world is losing species at a rate that is 100 to 1000 times faster than the natural extinction rate

Extinction ◦ Effects of natural extinction:  provided ecological opportunities for organisms that survived  resulted in bursts of evolution that produced many new species 11-6: Patterns of Evolution

Adaptive Radiation ◦ Process by which a single species or a small group of species evolves into several different forms that live in different ways. ◦ Example:  More than a dozen species of Darwin’s finches evolved from a single species 11-6: Patterns of Evolution

Adaptive Radiation 11-6: Patterns of Evolution

Adaptive Radiation 11-6: Patterns of Evolution

Convergent Evolution ◦ Different organisms undergo adaptive radiation in different places or at different times but in similar environments. ◦ The process by which unrelated organisms come to resemble one another is called convergent evolution. Results in analogous structures. 11-6: Patterns of Evolution

Co-Evolution ◦ Sometimes organisms that are closely connected to one another by ecological interactions evolve together. ◦ The process by which two species evolve in response to changes in each other over time is called coevolution. 11-6: Patterns of Evolution

Punctuated Equilibrium ◦ Darwin felt that biological change was slow and steady, an idea known as gradualism ◦ Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. 11-6: Patterns of Evolution

Punctuated Equilibrium 11-6: Patterns of Evolution

Developmental Genes and Body Plans ◦ Hox Genes are the master control genes of body layout. 11-6: Patterns of Evolution

Developmental Genes and Body Plans 11-6: Patterns of Evolution