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CHAPTER 16 EVOLUTION OF POPULATIONS POPULATION GENETICS Study of evolution from a genetic point of view. Study of the change in the GENE POOL for a population Example- in a garden what percent of the roses are Red (RR), pink (Rr) or white (rr) ALLELES Possible traits of a gene ALLELE FREQUENCY- how common a specific allele is in the gene pool PHENOTYPE FREQUENCY- how common a specific phenotype is in a population ALLELE FREQUENCY ALLELE FREQUENCIES VS PHENOTYPE FREQUENCIES Although phenotype frequencies tend to change generation to generation. Allele frequencies tend to stay the same. HARDY WEINBERG EQUILIBRUIM--p2 + 2pq + q2 = 1 HARDY WEINBERG EQUILIBRUIM1. mutation is not occurring 2. there is no migration in or out of the population 3. the population is infinitely large 4. natural selection is not occurring 5. all members of the population breed 6. everyone produces the same number of offspring 7. all mating is totally random MUTATIONS Can add a new allele into the mix IMMIGRATION or EMIGRATION- can add or subtract a bunch of individuals with one specific allele SMALL POPULATIONS GENETIC DRIFT- the alelle frequency chances simply due to chance link to Simulation notice how the value for P will either climb to 1 or go all the way down to 0 http://darwin.eeb.uconn.edu/simulations/drift.ht ml NO NATURAL SELECTION All individuals have to have an equal chance of survival reproduction and have the same fitness. RANDOM MATING (NO SEXUAL SELECTION) NO ASSORTATIVE MATING All individuals must reproduce at the same rate. BELL CURVE OF PHENOTYPES STABILIZING SELECTION Individuals with the most average form of a trait have the highest fitness Graph– gets taller and narrower in the middle BELL CURVE OF PHENOTYPES DIRECTIONAL SELECTION Individuals that have one extreme of a trait show a higher fitness Center of the graph moves in one direction BELL CURVE OF PHENOTYPES DISRUPTIVE SELECTION Individuals at either extreme have the highest fitness ****This can lead to one species become two different species. Single parabola slowly turns into 2 parabolas BELL CURVE OF PHENOTYPES MICROEVOLUTION VS MACROEVOLUTION Micro-- small changes in a species Macro- large transformations in a species MICROEVOLUTION is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection (natural and artificial), gene flow, and genetic drift. GENETIC DRIFT ----OR ALLELIC DRIFT is the change in the frequency of a gene variant (allele) in a population due to random sampling. occurs in smaller populations much faster FOUNDER’S EFFECT is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. BOTTLENECK a sharp reduction in size of a population due to environmental events (such as earthquakes, floods, fires, or droughts) or human activities. BOTTLENECK EXAMPLES One real life example of a species being affected by the bottleneck effect is the northern elephant seal. Humans intensely hunted these animals in the late nineteenth century, and their population was reduced to just twenty at one point. Though the species has recovered and there are over 30,000 northern elephant seals today, there is not a lot of genetic diversity among members of this species. WHY IS A BOTTLENECK BAD? Less genetic diversity More likely to reveal RECESSIVE genes BOTTLENECK EXAMPLES --Any ENDANGERED SPECIES ---Giant Panda --- Prairie Chicken --- Amish ---Inhabitants of small islands (Iceland) MICROEVOLUTION BY ISOLATION REPRODUCTIVE ISOLATION-- individuals are split from the rest of the population due to some type of barrier TYPES OF ISOLATION GEOGRAPHIC ISOLATION- populations that have been separated by physical barriers --Mountain ranges --Rivers- (Grand Canyon) --Ocean- (organisms separated on different islands) --Human Interference ---dams, highways, fences TYPES OF ISOLATION BEHAVIORAL ISOLATION– (ethological)-- - various courtship rituals or other behaviors interfere with interbreeding Ex- Eastern and Western Meadowlark have different songs. Crickets are very species specific in their songs TYPES OF ISOLATION TEMPORAL ISOLATION-- species that reproduce at different times Flocks of Canadian Geese migrating at different times Flowers that bloom at different times TEMPORAL ISOLATION- PREZYGOTIC VS POSTZYGOTIC BARRIERS PREZYGOTIC-- prevents reproduction- (geographic, temporal, behavioral) POSTZYGOTIC BARRIERHybrid inviability: hybrid fails to develop or fails to reach sexual maturity- usually due to chromosomal differences Behavioral sterility: hybrid reaches sexual maturity but fails to produce appropriate courtship displays or mating behavior (plants may grow flowers that fail to attract pollinators) Hybrid sterility: hybrids fail to produce functional gametes MACROEVOLUTION Large changes in a species Rate of EVOLUTION 1. GRADUALISM 2. PUNCTUATED EQUILIBRIUM GRADUALISM Defined as a profound change being the sum of many slow and steady changes Ex- ostrich wings becoming smaller and smaller as the birds evolved. PUNCTUATED EQUILIBRIUM “rapid evolution” due to large changes in the environment Examples volcanoes forming new islands Small group becomes isolated New species enters the ecosystem ADAPTIVE RADIATION Single species or small group of species evolves into several different forms Ex- Mammals where quite small species during the days of the dinosaur. When the dinosaurs went extinct many species began large changes. (elephants, whales, rhino) Darwin’s finches- one species of finch turns into many different species.
