MECHANISMS FOR MECHANISMS FOR EVOLUTIONEVOLUTION

CHAPTER 23CHAPTER 23

ObjectivesObjectives– State the Hardy-Weinburg theoremState the Hardy-Weinburg theorem– Write the Hardy-Weinburg equation and be Write the Hardy-Weinburg equation and be

able to use it to calculate allele and genotype able to use it to calculate allele and genotype frequenciesfrequencies

– List the conditions that must be met to maintain List the conditions that must be met to maintain Hardy Weinburg equilibriumHardy Weinburg equilibrium

VOCABULARYVOCABULARY

POPULATIONPOPULATION SPECIESSPECIES GENE POOLGENE POOL GENE FLOWGENE FLOW BOTTLENECK BOTTLENECK

EFFECTEFFECT FOUNDER EFFECTFOUNDER EFFECT HETEROZYGOTE HETEROZYGOTE

ADVANTAGEADVANTAGE

HYBRID VIGORHYBRID VIGOR STABILIZING STABILIZING

SELECTIONSELECTION DIRECTIONAL DIRECTIONAL

SELECTIONSELECTION DIVERSIFYING DIVERSIFYING

SELECTIONSELECTION SEXUAL SEXUAL

DIMORPHISMDIMORPHISM

POPULATIONPOPULATION– Localized group belonging to the same speciesLocalized group belonging to the same species

SPECIESSPECIES– Naturally breeding group of organisms that Naturally breeding group of organisms that

produce fertile offspringproduce fertile offspring GENE POOLGENE POOL

– Total aggregate of genes in a population at any Total aggregate of genes in a population at any one timeone time

Most species are not evenly distributed over a Most species are not evenly distributed over a geographic range. Individuals are more likely geographic range. Individuals are more likely to breed with others from their population to breed with others from their population centercenter

HARDY – WEINBURG THEOREMHARDY – WEINBURG THEOREM

Describes a NON-EVOLVING populationDescribes a NON-EVOLVING population In the absence of other factors the In the absence of other factors the

segregation and recombination of alleles segregation and recombination of alleles during meiosis and fertilization will not during meiosis and fertilization will not alter the overall genetic make-up of a alter the overall genetic make-up of a populationpopulation

Imagine an isolated Imagine an isolated wildflower population wildflower population with the following with the following characteristicscharacteristics– Diploid with both pink Diploid with both pink

and white flowersand white flowers

– Pink is dominant A and Pink is dominant A and white is recessive awhite is recessive a

– There are 480 pink There are 480 pink flowers and 20 whiteflowers and 20 white

» 320 are AA320 are AA

» 160 are Aa160 are Aa

(p + q)2 = 1

p + q = 1

p2 + 2pq +q2 = 1

pp22 = frequency of AA = frequency of AA 2pq = frequency of Aa2pq = frequency of Aa qq22 = frequency of aa = frequency of aa Calculate qCalculate q2 2 firstfirst There are 1000 allelesThere are 1000 alleles

– AA -- 320 x 2/plant = 640AA -- 320 x 2/plant = 640– Aa --160 x 1/plant =Aa --160 x 1/plant = 160 160

800800– aa -- 20 x 2/plant = 40aa -- 20 x 2/plant = 40– Aa – 160 x 1/plant =Aa – 160 x 1/plant =160160– 200200– Frequency of A = 80% and a = 20%Frequency of A = 80% and a = 20%

Condition for Hardy-WeinburgCondition for Hardy-Weinburg

Large populationLarge population No net mutationNo net mutation Isolated populationIsolated population Random matingRandom mating No natural selectionNo natural selection

MICROEVOLUTION MICROEVOLUTION

LEADS TOLEADS TOMACROEVOLUTIONMACROEVOLUTION

CAUSES OF CAUSES OF MICROEVOLUTIONMICROEVOLUTION

GENETIC DRIFTGENETIC DRIFT

– BOTTLENECK EFFECTBOTTLENECK EFFECT

– FOUNDER EFFECTFOUNDER EFFECT

GENE FLOW – genetic exchange GENE FLOW – genetic exchange between populations due to migrationbetween populations due to migration

Mutation – a new mutation that is Mutation – a new mutation that is transmitted in a gamete can immediately transmitted in a gamete can immediately change the gene poolchange the gene pool

NONRANDON MATINGNONRANDON MATING– Breed with other members of the Breed with other members of the

“neighborhood” promotes inbreeding“neighborhood” promotes inbreeding– Assortative mating – mate with others like Assortative mating – mate with others like

themselvesthemselves NATURAL SELECTIONNATURAL SELECTION

Variation within PopulationsVariation within Populations

Most heritable variation is measured byMost heritable variation is measured by– Quantitative characters (vary along a Quantitative characters (vary along a

continuum ie. Height) are polygeneticcontinuum ie. Height) are polygenetic– Discrete characters (pink or white) are Discrete characters (pink or white) are

located on a single genelocated on a single gene

Polymorphism – two or more forms of a Polymorphism – two or more forms of a discrete character are represented in a discrete character are represented in a populationpopulation

GEOGRAPHICAL GEOGRAPHICAL VARIATIONVARIATION

A cline is a graded change in some trait along a geographical axis.

MODES OF SELECTIONMODES OF SELECTION