Adaptation and VariationThe Evolutionary process:1. Variation2. Natural Selection 3. Genetic Divergence 4. Reproductive Isolation5. SpeciationVariationNatural SelectionReproductive isolationGenetic DivergenceSpeciationPopulations evolve not individuals Populations have variation in traits among individualsMicroevolution: The change in allele frequencies in a population over generations.Adaptation and VariationFeatures that characterize a population:1. Morphological traits (Form)2. Physiological traits (Function) 3. Ethological traits (Behavior)In reproducing species there is variation in most traits in individuals (Individuals of a population vary in their traits)- Discrete characters: either – or basis (2 or more distinct forms) - Quantitative characters: vary along a continuumAdaptation and VariationVariation:Adaptation: Adjustment or change to meet environmental conditionsTraits may be positive, negative or neutral to individuals in a population (survival and reproduction)1. Adaptive Traits (+)- form of trait that is an advantage in terms of survival & reproduction2. Maladaptive Traits (-)- form of trait that is a disadvantage in terms of survival & reproduction3. Neutral Traits (0)- form of trait that is neither a disadvantage or advantage in terms of survival and reproductionAlmost every trait or every species is variableAdaptation and VariationVariation:(Information about heritable traits occurs in genes)Where does variation come from? Gene Pool: All the genes in a population (pool of genetic resources)Genome: All the genes in a speciesGenotype: Individuals inherit different combinations of alleles(genetic expression)Phenotype: Individuals express different details of traits(physical expression)Gene: Hereditary unit of DNA that codes for specific traitsAlleles: 2 or more different molecular forms of a gene(alternate form of a gene – dominant, recessive, incomplete dominance)Adaptation and VariationVariation: Individuals inherit different combinations of alleles which leads to variation in phenotypeWhich alleles end up in a given gamete, and individual? 5 events:1. Gene mutation (produces new alleles) 2. Crossing over at meiosis I (puts novel combinations of alleles in chromosomes)3. Independent assortment at meiosis I (puts mixes of maternal and paternal chromosomes into gametes) 4. Fertilization (combines alleles from two parents) 5. Change in chromosome number or structure) (the loss, duplication, or repositioning of genes)Ex: Each human gamete = 10600 possible allelic combinationsAdaptation and VariationPhenotypic Frequencies: The abundance of phenotype in a populationEx: Eye color Brown Blue Green Hazel(gross simplification) 25 (BB) 20 (bb) 3 2Each genotype has a distinct phenotypePhenotype FrequencyBrown 25/50 X 100 = 50%Blue 20/50 X 100 = 40%Green 3/50 X 100 = 6%Hazel 2/50 X 100 = 4%100%Adaptation and VariationEx: Wildflowers (Flower color, incomplete dominance, 2 alleles A & a) Red White Pink Pop. Size320 (AA) 20 (aa) 160 (Aa) = 500 (Diploid = 1000 copies of genes)With this information, can track the rate of genetic change over multiple generationsAllele Frequencies: The abundance of each kind of allele in a populationAA 320 X 2 = 640Aa 160 X 1 = 160 800 A allelesaa 20 X 2 = 40Aa 160 X 1 = 160200 a alleles800 / 1000 = 0.8 = 80% A allele200 / 1000 = 0.2 = 20% a allele100% A & a AllelesAdaptation and VariationAllele Frequencies:Is there genetic change over generations?Genetic equilibrium: The frequencies of alleles at a given gene locus remain stable for multiple generationsQuestion:1. How do we know whether or not a population is evolving with respect to any trait?Answer: Hardy – Weinberg Principle (1908) Mathematical formulation to describe how to maintain the frequencies of alleles of a population over timeAdaptation and VariationHardy – Weinberg Principle (1908):In a population in genetic equilibrium:1. The proportion of genotypes at one gene locus with two kinds of alleles (Binomial Expansion)p = the frequency of allele (A) q = the frequency of allele (a)p2(AA) + 2pq (Aa) + q2(aa) = 1The rule is, allele frequencies will be stable through successive generations if:1. there has been no gene mutations2. the population is very large3. the population is isolated4. the gene has no effect on survival and reproduction5. mating is randomAdaptation and VariationHardy – Weinberg Equilibrium:Example: Butterfly wing color (pairs of genes on pairs of homologous chromosomes)1. Assume the population is at equilibrium2. Pair of alleles is for wing color:allele A = dark blue wingsallele a = white wingsHeterozygote Aa = light blue wings (incomplete dominance)3. The frequencies of A and a must add up to 1 in the population:p + q = 1AAaaAaAdaptation and VariationHardy – Weinberg Equilibrium:4. During meiosis: each allele segregates from its partnerand ends up in separate gametesp = the proportion of gametes carrying the (A) allele q = the proportion of gametes carrying the (a) alleleExpected frequencies of the 3 genotypes (AA, aa, Aa) in the next generation:AA (p2)aa (q2)Aa (pq)Aa (pq)p (A)q (a)p (A)q (a)The frequencies of the genotypes add up to 1:p2(AA) + 2pq (Aa) + q2(aa) = 1Adaptation and VariationHardy – Weinberg Equilibrium:Example: 1000 butterflies (each produces 2 gametes)490 AA individuals produce 980 A gametes420 Aa individuals produce 420 A and 420 a gametes90 aa individuals produce 180 a gametes2000 gametesp = (980 + 420) / 2000 = 0.7 = 70% (A)The frequency of A and a alleles among the 2000 gametes:q = (420 + 180) / 2000 = 0.3 = 30% (a)Adaptation and VariationAt fertilization:1. Gametes combine at random, give rise to the next generation 2. Assume, population remains constant at 1000 individualsp2(AA) = 0.7 X 0.7 = 0.49 X 1000 490 AA individuals2pq (Aa) = 2 X 0.7 X 0.3 = 0.42 X 1000 420 Aa individualsq2(aa) = 0.3 X 0.3 = 0.09 X 1000 90 aa individualsp2(AA) + 2pq (Aa) + q2(aa) = 0.49 + 0.42 + 0.09 = 1Hardy – Weinberg Equilibrium:Allele frequencies have not changed:A = [(2 X 490) + 420] / 2000 = 1400/2000 = 0.7 = pa = [(2 X 90) + 420] / 2000 = 600/2000 = 0.3 = qGenotype frequencies have not changed: .49, .42, .09Adaptation and VariationAs long as the 5 basic assumptions are met:- The frequencies stay the same through successive generations0.49 + 0.21Test: by calculating frequencies in the gametes of the next generationF1genotypes 0.49 (AA) 0.42 (Aa) 0.09 (aa)A A0.3