MECHANISMS FOR EVOLUTION CHAPTER 23

Objectives Objectives –State the Hardy-Weinburg theorem –Write the Hardy-Weinburg equation and be able to use it to calculate allele and genotype frequencies –List the conditions that must be met to maintain Hardy Weinburg equilibrium

VOCABULARY POPULATION POPULATION SPECIES SPECIES GENE POOL GENE POOL GENE FLOW GENE FLOW BOTTLENECK EFFECT BOTTLENECK EFFECT FOUNDER EFFECT FOUNDER EFFECT HETEROZYGOTE ADVANTAGE HETEROZYGOTE ADVANTAGE HYBRID VIGOR STABILIZING SELECTION DIRECTIONAL SELECTION DIVERSIFYING SELECTION SEXUAL DIMORPHISM

POPULATION POPULATION –Localized group belonging to the same species SPECIES SPECIES –Naturally breeding group of organisms that produce fertile offspring GENE POOL GENE POOL –Total aggregate of genes in a population at any one time Most species are not evenly distributed over a geographic range. Individuals are more likely to breed with others from their population center

HARDY – WEINBURG THEOREM Describes a NON-EVOLVING population Describes a NON-EVOLVING population In the absence of other factors the segregation and recombination of alleles during meiosis and fertilization will not alter the overall genetic make-up of a population In the absence of other factors the segregation and recombination of alleles during meiosis and fertilization will not alter the overall genetic make-up of a population

Imagine an isolated wildflower population with the following characteristics Imagine an isolated wildflower population with the following characteristics –Diploid with both pink and white flowers –Pink is dominant A and white is recessive a –There are 480 pink flowers and 20 white »320 are AA »160 are Aa (p + q) 2 = 1 p + q = 1 p 2 + 2pq +q 2 = 1

p 2 = frequency of AA p 2 = frequency of AA 2pq = frequency of Aa 2pq = frequency of Aa q 2 = frequency of aa q 2 = frequency of aa Calculate q 2 first Calculate q 2 first There are 1000 alleles There are 1000 alleles –AA x 2/plant = 640 –Aa x 1/plant = –aa x 2/plant = 40 –Aa – 160 x 1/plant =160 – 200 –Frequency of A = 80% and a = 20%

Condition for Hardy-Weinburg Large population Large population No net mutation No net mutation Isolated population Isolated population Random mating Random mating No natural selection No natural selection

MICROEVOLUTION LEADS TO MACROEVOLUTION

CAUSES OF MICROEVOLUTION CAUSES OF MICROEVOLUTION GENETIC DRIFT GENETIC DRIFT –BOTTLENECK EFFECT BOTTLENECK EFFECTBOTTLENECK EFFECT –FOUNDER EFFECT FOUNDER EFFECTFOUNDER EFFECT

GENETIC DRIFT GENETIC DRIFT

BOTTLENECK EFFECT

FOUNDER EFFECT FOUNDER EFFECT

GENE FLOW – genetic exchange between populations due to migration GENE FLOW – genetic exchange between populations due to migration Mutation – a new mutation that is transmitted in a gamete can immediately change the gene pool Mutation – a new mutation that is transmitted in a gamete can immediately change the gene pool NONRANDON MATING NONRANDON MATING –Breed with other members of the “neighborhood” promotes inbreeding –Assortative mating – mate with others like themselves NATURAL SELECTION NATURAL SELECTION

Variation within Populations Most heritable variation is measured by Most heritable variation is measured by –Quantitative characters (vary along a continuum ie. Height) are polygenetic –Discrete characters (pink or white) are located on a single gene Polymorphism – two or more forms of a discrete character are represented in a population Polymorphism – two or more forms of a discrete character are represented in a population

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

MODES OF SELECTION