The Evolution of Populations Chapter 23 The Evolution of Populations

Population Genetics Darwin and Mendel Gene pool and Allele frequency fixed Heterozygous Mind your p’s and q’s!

Calculate allele frequencies: 500 total flowers 320 red 160 pink Generation 1 X CRCR CWCW genotype genotype Calculate allele frequencies: 500 total flowers 320 red 160 pink 20 white Freq CR: FreqCW: Plants mate Generation 2 All CRCW (all pink flowers) 50% CR 50% CW gametes gametes come together at random Generation 3 25% CRCR 50% CRCW 25% CWCW 50% CR 50% CW gametes gametes come together at random Generation 4 25% CRCR 50% CRCW 25% CWCW Alleles segregate, and subsequent generations also have three types of flowers in the same proportions

The Hardy-Weinberg Theorem Allele frequencies in a population remain unchanged Basis for understanding long-term evolutionary changes H-W equilibrium – p2 + 2pq + q2 = 1 p + q = 1

Gametes for each generation are drawn at random from the gene pool LE 23-5 Gametes for each generation are drawn at random from the gene pool of the previous generation: 80% CR (p = 0.8) 20% CW (q = 0.2) Sperm CR (80%) CW (20%) p2 pq (80%) CR Eggs 64% CRCR 16% CRCW (20%) CW 16% CRCW 4% CWCW qp q2

Conditions for Hardy-Weinberg Large population size No gene flow No mutations Random mating No natural selection

Sources of Variation Mutations Sexual recombination Point mutation Alter gene number or sequence duplication Mutation rates Sexual recombination

Altering Populations Gene Pool: The Big Players Natural selection Genetic Drift Bottleneck effect Founder effect Gene flow

LE 23-7 CRCR CRCR CWCW CRCR CRCR CRCW CRCW CRCR CRCR CWCW CRCR CRCR Only 5 of 10 plants leave offspring CRCW Only 2 of 10 plants leave offspring CRCR CRCR CWCW CRCR CRCR CWCW CRCR CRCR CRCW CRCW CRCR CRCR CRCR CRCW CWCW CRCR CRCR CRCR CRCW CRCW CRCW CRCR CRCR Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0

LE 23-8 Original population Bottlenecking event Surviving population

Natural Selection and Adaptive Evolution Genetic variation Polymorphism Geographic variation Closer look at Natural Selection Evolutionary fitness Types of selection Preservation of genetic variation Sexual Selection

LE 23-10 1 2.4 3.14 5.18 6 7.15 8.11 9.12 10.16 13.17 19 XX 1 2.19 3.8 4.16 5.14 6.7 9.10 11.12 13.17 15.18 XX

Mean height (cm) Altitude (m) Sierra Nevada Range Great Basin Plateau LE 23-11 Heights of yarrow plants grown in common garden 100 Mean height (cm) 50 3,000 Altitude (m) 2,000 Sierra Nevada Range Great Basin Plateau 1,000 Seed collection sites

Frequency of individuals LE 23-12a Original population Frequency of individuals Phenotypes (fur color)

LE 23-12b Original population Evolved population Directional selection Disruptive selection Stabilizing selection

Plasmodium falciparum (a protozoan) LE 23-13 Frequencies of the sickle-cell allele 0–2.5% 2.5–5.0% 5.0–7.5% Distribution of malaria caused by Plasmodium falciparum (a protozoan) 7.5–10.0% 10.0–12.5% >12.5%

LE 23-14 On pecking a moth image the blue jay receives a food reward. If the bird does not detect a moth on either screen, it pecks the green circle to continue a new set of images (a new feeding opportunity). Parental population sample 0.6 Experimental group sample 0.5 Phenotypic variation 0.4 Frequency- independent control 0.3 0.2 20 40 60 80 100 Generation number Plain background Patterned background