1. Ch. 16 The Evolution of Populations and Speciation

2. Background Information Genetics- the study of heredity; how traits are passed from parents to offspring Allele- an alternative form of a gene; – Ex: alleles for tallness in pea plants TT - tall; tt - short; Genotype- the genetic makeup of an organism for a trait; Tt –Ex: Tt Phenotype- the physical make-up of an organism, what the organism physically looks like; Tall –Ex: Tall

3. Genetic Equilibrium Population Genetics- the study of evolution from a genetic point of view. –Bell curve- useful tool used to show variation in traits or characteristics w/in a population of a species. some variations are caused by the environment; heredity; both usually play a role population variations. –Variations arise from: »1. Mutation- flawed copies of genes. »2. Recombination- reassociation of genes. »3. Random fusion of gametes- the game of chance of gamete fusion –Gene pool- used to describe the total genetic information available in a population. allows allele frequencies to be predicted if present alleles w/in population are known; predict genotypes for future generations.

4. Allele Frequency- divide the # of a certain allele by the total # of ALL alleles in the population. -Ex: 12/16=.75 (‘R’ frequency) 4/16=.25 (‘r’ frequency) Phenotype Frequency- the # of indiv. w/ a particular phenotype divided by the total # of indiv. in the population. -Ex: 1/8= 0.125 (white four o’clock flowers) 2/8= 0.25 (pink four o’clock) 5/8= 0.625 (red four o’clock)

5. Wilhelm Weinberg (German physician) and Godfrey Hardy (British mathematician)Wilhelm Weinberg (German physician) and Godfrey Hardy (British mathematician) –wanted to answer what happened to allele frequencies over generations. –independently they showed that allele frequencies will remain the same w/in a population over multiple generations as long as there are no outside influences on the population. Their idea is based upon an ideal hypothetical population that is not evolving.

6. Hardy-Weinberg Genetic Equilibrium 1.NO net mutations occur. 2.Individuals neither enter nor leave the population. 3.The population is large (ideally, infinitely large). 4.Individuals mate randomly. 5.Selection does not occur. True genetic equilibrium is a theoretical state. “Hardy-Weinberg genetic equilibrium allows us to consider what forces disrupt equilibrium.” (Modern Biology © 2009) *any change in the 5 conditions can result in evolution*

7. Disruption of Genetic Equilibrium 1.) Mutation 2.) Migration Immigration Migration 3.) Genetic Drift 4.) Nonrandom Mating 5.) Natural Selection Stabilizing Selection Directional Selection Disruptive Selection Sexual Selection

8. 1. Mutation- will cause frequency changes by creating new alleles to be introduced into the population. 2. Migration- will cause frequency changes because the population will not remain constant. Immigration- individuals move into a population. Emigration- individuals move out of a population. –can cause gene flow- the process of genes moving from 1 population to another 3. Genetic Drift- allele frequencies are controlled by random events or chance. can cause extinction of a species because a lack of variation of alleles for specific traits; becomes a serious issue for small populations. –the failure of even 1 organism to reproduce or 1 to reproduce above norm can extensively disrupt allele frequency.

9. 4. Nonrandom Mating- species select mates according to similarities in physical traits. called assortative mating. usually influenced by geographical proximity. –Random mating would indicate mating w/out regard to genetic make-up »random mating can affect the combination of alleles in a population but will not affect allele frequencies. 5. Natural Selection- individuals selecting mates according to favorable traits »single most disruptive factor to genetic equilibrium. A.Stabilizing Selection A. Stabilizing Selection- individuals w/ the average form of a trait have the highest fitness. –the average represents the optimum for most traits, the extreme forms of most traits relinquish lower fitness for those individuals that have them. » Selection against the extremes reduces # of organisms w/ the trait. –Most common type of selection.

10. B. Directional Selection B. Directional Selection- individuals w/ an extreme form of the trait have greater fitness than those individuals w/ the average form of the trait. –Usually will be dictated by an environmental change; coevolution C. Disruptive Selection C. Disruptive Selection- individuals w/ either extreme variation of a trait are more fit than individuals w/ the average form of the trait. D. Sexual Selection D. Sexual Selection- females choosing male mates based upon certain traits. –Genes of successful reproducers not of those that merely survive are amplified through natural selection.

11. Formation of Species Speciation- the formation of a new speciesSpeciation- the formation of a new species Morphology- the study of the internal and external structure and form of an organism.Morphology- the study of the internal and external structure and form of an organism. was used as the chief criterion for species classification, but had some limitations; it means there can be NO phenotypic differences w/in a population.was used as the chief criterion for species classification, but had some limitations; it means there can be NO phenotypic differences w/in a population. The biological species concept arose when biologists recognized that organisms which looked like different species interbred and produced fertile offspring.The biological species concept arose when biologists recognized that organisms which looked like different species interbred and produced fertile offspring. Proposed by American Biologist Ernest Mayr it says a species is a population that can successfully interbreed but not w/ other groups.Proposed by American Biologist Ernest Mayr it says a species is a population that can successfully interbreed but not w/ other groups. reasonable idea for sexually reproducing modern organisms; cannot be tested on extinct species nor is it useful in organisms that reproduce asexually.reasonable idea for sexually reproducing modern organisms; cannot be tested on extinct species nor is it useful in organisms that reproduce asexually.

12. Isolating Mechanisms Speciation begins w/ isolation because 2 parts of a formerly interbreeding population quit interbreeding Geographic Isolation- physical separation of members of a population.Geographic Isolation- physical separation of members of a population. »Habitat could become divided once subpopulations become isolated then gene flow ceases between them.once subpopulations become isolated then gene flow ceases between them. Reproductive Isolation- genetic isolation even w/out geographic isolation.Reproductive Isolation- genetic isolation even w/out geographic isolation. »May arise from disruptive selection. –Prezygotic isolation- occurs before fertilization –Postzygotic isolation- occurs after fertilization

13. Prezygotic IsolationPrezygotic Isolation These are mechanisms that prevent mating of organisms. »Incompatible behavior- different mating calls »Different mating times- spring/summer Postzygotic IsolationPostzygotic Isolation These are occurrences that happen after fertilization. »Offspring may die or not develop completely »Offspring may not be fertile therefore adults wasted their gametes Rates of SpeciationRates of Speciation –Speciation may occur gradually overtime or quickly. Gradual- species evolve gradually overtime. Punctuated equilibrium- species arise abruptly; a sudden shift in form.