Evolution Darwin’s Ideas Hardy-Weinberg Evidence for Evolution Speciation and Mechanisms Origins

How do genetic variations occur? What is Evolution? Change in the genetic makeup of a population over time. Fitness – those with favorable variations for survival and reproduction. Populations can evolve, not individuals. Diverse gene pool good for long-term survival of a species. Genetic variations are important! How do genetic variations occur?

Where does Variation come from? Mutation random changes to DNA errors in mitosis & meiosis environmental damage Sexual reproduction mixing of alleles genetic recombination new arrangements of alleles in every offspring new combinations = new phenotypes

Genetic variation in a population

Essence of Darwin’s ideas Natural selection heritable variation exists in populations over-production of offspring more offspring than the environment can support competition for food, mates, nesting sites, escape predators differential survival successful traits = adaptations differential reproduction adaptations become more common in population

Lamarckian vs. Darwinian view in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin giraffes born with longer necks survive better & leave more offspring who inherit their long necks 

Natural Selection Major mechanism of evolution Environment is always changing Acts upon the phenotype of the population Based on Darwin’s idea that resources are limited and that there is competition for those resources. Adaptation = a genetic variation favored by natural selection. When allele frequencies shift, speciation occurs Thus, the frequency change is NOT RANDOM

DIRECTIONAL SELECTION STABILIZING SELECTION Effects of Selection Changes in the average trait of a population DIRECTIONAL SELECTION STABILIZING SELECTION DISRUPTIVE SELECTION giraffe neck horse size human birth weight rock pocket mice

Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective Resistance… NOT immunity! MRSA

Heterozygote Advantage Keeps the recessive allele in the population Ex: Sickle Cell Anemia aa – dies of sickle cell anemia Aa – some side affects BUT resistant to malaria! AA – no disease present BUT prone to malaria

Hidden variations can be exposed through selection! Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Flower and stems Broccoli Wild mustard Kohlrabi Stem Kale Artificial selection

In addition to natural selection, evolutionary change is also driven by random processes…

Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection founder effect small group splinters off & starts a new colony it’s random who joins the group bottleneck a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool who survives disaster may be random Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists example: colonization of New World Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event alleles lost from gene pool not due to fitness, narrows the gene pool

Ex: Cheetahs All cheetahs share a small number of alleles less than 1% diversity 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

Peregrine Falcon Conservation issues Bottlenecking is an important concept in conservation biology of endangered species loss of alleles from gene pool reduces variation reduces adaptability Breeding programs must consciously outcross Golden Lion Tamarin

Human Impact on variation How do we affect variation in other populations? Artificial selection/Inbreeding Animal breeds Loss of genetic diversity Insecticide usage Overuse of antibiotics resistant bacterial strains