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MICROEVOLUTION on the Origin of Species… WHAT IS a SPECIES? • Individuals in One Or More Populations • Potential to Interbreed • Produce Fertile Offspring

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MICROEVOLUTION on the Origin of Species… WHAT IS a SPECIES? • Individuals in One Or More Populations • Potential to Interbreed • Produce Fertile Offspring Population Evolution MICROEVOLUTION On the Origin of Species… WHAT IS A SPECIES? • Individuals in one or more populations • Potential to interbreed • Produce fertile offspring WHAT IS A POPULATION? EVOLUTION OF POPULATIONS • Group of interacting individuals The Synthetic Theory of Evolution belonging to one species and living in – Applying population genetics the same geographic area to the Darwinian model • A population • Genetics & Variability is the smallest • Non-Adaptive Evolution unit that can • Fitness & Natural Selection evolve. • Sexual Selection Figure 23.6 Genes & Alleles Genetic variation: • Genes code for morphology, how do new forms arise? physiology, or behavior. • Point mutations: change code, change protein. • Gene for hair color or leg length. • Alleles are alternative forms genes can have: red hair, brown hair, etc. DNA RNA protein chain of amino acids Heyer 1 Population Evolution Genetic variation: Mutation Events Are Random how do new forms arise? • Chromosomal mutations of base sequences. • Mutations are destructive alterations to previously existing complex systems. • Most mutations are neutral or detrimental — very few are beneficial. • The need for a mutation to arise does not increase its probability. Genetic variation: Individual Variation how do new forms arise? • Crossing over between maternal & paternal • Individuals vary in bell-curve of phenotypes chromosome makes new genotypes. – phenotype = genotype + environment. • Due to different environments or genotypes – But only gene differences are passed on. # of ind. in popn. leg length amount of saliva produced rate of eye blinking Non-genetic Phenotypic Variation Alleles to Gene Pools • Environmentally induced phenotypic variations within the same genotype Alleles in an Alleles in all the individuals individual of the population (a) Map butterflies that (b) Map butterflies that emerge in spring: emerge in late summer: orange and brown black and white Figure 23.9 Heyer 2 Population Evolution The Hardy-Weinberg GENE POOL & FREQUENCY OF Generation 1 CRCR CWCW genotype genotype Theorem ALLELES IN THE POPULATION Plants mate • If gametes contribute to the next • Gene pool is the total Generation 2 generation randomly, Mendelian collection of genes All CRCW (all pink flowers) and their variations segregation and recombination of alleles 50% CR 50% CW (alleles) in a gametes gametes preserves genetic variation in a population Come together at random population • Reservoir of Generation the frequencies of alleles and 3 \ variations from 25% CRCR 50% CRCW 25% CWCW genotypes in a population’s gene pool which the next 50% CR 50% CW remain constant from generation to generation derives its gametes gametes Come together at random generation genes Generation • Polymorphic 4 Allelic frequency= 25% CRCR 50% CRCW 25% CWCW Alleles segregate, and subsequent 49% AA + 42% Aa + 9% aa = 70% A + 30% a generations also have three types of flowers in the same proportions Figure 23.4 A population in A population in Hardy-Weinberg equilibrium Hardy-Weinberg equilibrium • p = frequency of occurrence of the CR allele in the population • p = frequency of occurrence of the CR allele in the population • q = frequency of occurrence of the Cw allele in the population • q = frequency of occurrence of the Cw allele in the population Then: Gametes for each generation are drawn at random from 64% CRCR, 32% CRCW, and 4% CWCW the gene pool of the previous generation: 80% CR 20% CW 80% CR 20% CW (p = 0.8) (q = 0.2) Gametes of the next generation: (p = 0.8) (q = 0.2) R R 64% C from + 16% C from R R R W Sperm C C homozygotes C C homozygotes R W Sperm C C CR CW R (80%) (20%) (80%) (20%) = 80% C = 0.8 = p W W 2 16% 16% 4% C from 16% C from p R W pq p2 pq + C C CRCW CWCW homozygotes CRCW heterozygotes R R W C C = 20% C = 0.2 = q (80%) (80%) 16% 16% R W C C CRCW With random mating, these gametes will result in Eggs Eggs the same mix of plants in the next generation: 64% q2 4% 64% 2 4% W qp q R R W W W qp C C C C C R R W W C C C C C (20%) (20%) If the gametes come together at random, the genotype 64% CRCR, 32% CRCW, and 4% CWCW 64% CRCR, 32% CRCW and 4% CWCW plants frequencies of this generation are in Hardy-Weinberg equilibrium: again! R R R W W W 64% C C , 32% C C , and 4% C C Figure 23.5 Figure 23.5 A population in BIOLOGICAL EVOLUTION Hardy-Weinberg equilibrium • Change in a population’s gene pool over time as a result of a • If p and q represent the relative frequencies of change in frequency of an allele the only two possible alleles in a population at a particular locus, then 2 2 q p + 2pq + q = 1 • p2 = frequency of the genotype homozygous for the first allele • q2 = frequency of the genotype homozygous for the first allele • 2pq = frequency of the heterozygous genotype 70% A + 30% a 50% A + 50% a Heyer 3 Population Evolution BIOLOGICAL EVOLUTION BIOLOGICAL EVOLUTION • Change in a population’s gene pool over time as a result of a change • Change in a population’s gene pool over time as a result of a in frequency of an allele change in frequency of an allele • But according to Hardy-Weinburg Equilibrium: if mating is random, • But according to Hardy-Weinburg Equilibrium: if mating is the frequency of alleles in a population remains constant over time. random, the frequency of alleles in a population remains constant over time. • Therefore, population evolution is a product of non-random mating. 70% A + 30% a 70% A + 30% a A population in Hardy-Weinberg equilibrium BIOLOGICAL EVOLUTION • The five conditions for Hardy-Weinberg equilibrium: ¸ Large population size Remember! — ¸ No significant gene flow • Natural selection works on phenotype ¸ Mutation rate is trivial compared to recombination ¸ Random mating – But only genotype is inherited ¸ No significant natural selection • If any/several of these conditions are not met, changes • Natural selection works on individuals in allele frequency may occur – But only populations evolve ÿ non-equilibrium = evolution Non-Adaptive Evolution: EVOLUTION OF POPULATIONS Most Likely in Small Populations • Genetics & Variability • Genetic Drift • Non-Adaptive Evolution • Genetic Bottleneck • Fitness & Natural Selection • Founder Effect • Sexual Selection • Gene Flow • Assortative Mating Heyer 4 Population Evolution Genetic Drift • Random changes in gene frequencies. Non-Adaptive Evolution – it can lead to homozygosity. • Genetic Drift • Genetic Bottleneck • Founder Effect • Gene Flow • Assortative Mating VARIATION IN CHEETAH Genetic Bottleneck POPULATIONS • Few survive a population crash – cheetahs – elephant seals (~20) Founder Effect Non-Adaptive Evolution • Genetic Drift • Genetic Bottleneck • Founder Effect • Gene Flow • Assortative Mating • A few individuals disperse to new place – ABO frequencies of Dunkers in PA vs. Germany. Heyer 5 Population Evolution Non-Adaptive Evolution Gene Flow • Genetic Drift • Breeding w/ outsiders • Genetic Bottleneck – Spaniards in Central America • Founder Effect • Gene Flow • Assortative Mating Non-Adaptive Evolution: Non-adaptive Evolution: Significant only in small populations. Nonrandom mating * Genetic Drift: random changes in gene freq. • Assortative Mating: with those who look * Genetic Bottleneck: few survive pop. crash most like you. ÿ cheetahs & elephant seals • Sexual Selection: coming soon! * Founder Effect: few disperse to new place ÿ ABO frequencies of Dunkers in PA vs. Germany. * Gene Flow: breeding w/ outsiders ÿ Spaniards in Central America * Æ↑ homozygosity. * ÆØ homozygosity. Terms used in Natural Selection EVOLUTION OF POPULATIONS • Fitness: measure of how many genes you pass on to future generations. • Genetics & Variability • Differential representation of genes in future • Non-Adaptive Evolution generations due to differential survival to • Fitness & Natural Selection reproductive maturity. – Modes of Selection – Requires heritable (genetic) variation among • Sexual Selection individuals. • If differential survival is based upon expressed genotypic differences – it may lead to changes in population gene frequency. Heyer 6 Population Evolution Fitness and Selection “Survival of the fittest” • Darwinian fitness is a relative measure – how many offspring does one individual leave relative to others in the population. • Inheritance acts upon genotype “Reproduction • Selection acts upon phenotype – morphology, physiology, or behavior of the fittest” • Agents of selection – physical environment – biological environment • con- or hetero-specifics. Modes of Selection Modes of Selection • Fitness and Selection • Stabilizing Selection • Directional Selection • Diversifying Selection Heterozygote Advantage and the Stabilizing Selection: Sickle Cell Gene Human Birth-weights • HbS is a recessive allele for the hemoglobin gene • 1/11 African Americans are carriers • 1/500 are homozygous recessive (sickle cell disease) Heyer 7 Population Evolution MALARIA AND SICKLE CELL DISEASE Heterozygote Advantage: Malaria and Sickle Cell Anemia Directional Selection: Modes of Selection The Pepper Moth Biston betularia • Fitness and Selection • Stabilizing Selection • Directional Selection • Diversifying Selection Industrial melanism in early 1900’s EVOLUTION OF PEST Directional Selection: RESISTANCE The Pepper Moth Biston betularia • Red gene confers resistance to pesticide • Insecticide application • Only individuals carrying red gene survive • Red gene increases in population Heyer 8 Population Evolution MALARIA TODAY MALARIAL RESISTANCE • Mostly under control in 1947 • Common today in tropical countries • Kills 2.7
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