Evolution Continued

Evolution Continued Chapter 16: pgs 392 – 415 Chapter 17: pgs 416 - 445

Variation & Gene Pools • Gene Pool- consists of all genes, including all the different alleles, present in a population • Allele- One of a number of different forms of a gene • Relative Frequency- The number of times that the allele occurs in a gene pool • Has nothing to do with the gene being dominant or recessive • Example: Mice being black or brown • Evolution- any change in the relative frequency of alleles in a population

Genetic Variation • Recall- Genetics is a game of chance • Certain Individuals in Small populations pass on particular alleles • Overtime this can cause alleles to appear frequent

Sources of Genetic Variation • Mutations -Any change in a sequence of DNA • Either by mistake in replication OR radiation/chemical • Gene Shuffling- The different combination that occur when two organisms mate • You look like a combination of both parents • Many different combinations

Natural Selection • Natural selection on single-gene traits can lead to changes in allele frequencies and thus evolution • Single-gene trait- A single gene that has two alleles (example: Different species colors) • Mice that stand out get eaten faster • Therefore, Less Likely to survive to reproduce

Natural Selection Continued • Polygenic Traits- Traits controlled by two or more genes (example: height) • Directional Selection- Characteristics of one species is favored Example: Beak Size • Larger VS Smaller (Food Shortage) • Stabilizing Selection- Human baby birth weight • Smaller babies = less healthy • Larger= birth problems

Testing Natural Selection in Nature • Variation • When same species has different anatomical features • Color, size, beaks, total mass • Example: Finches • Natural Selection • Rainy Season VS Dry Season • Rainy = Numerous Sources of Food • Dry = Depleted/Scare sources • These differences create Natural Selection • Rapid Evolution • Once differences occur, species can change features relatively quickly (Each breeding season beaks get bigger

Genetic Drift • In small populations alleles can become more or less common • Controlled by probability • Occurs when a random change of traits occur over time • Such as animals colonizing a new habitat

Genetic Equilibrium • Hardy-Weinberg Principle • Allele frequencies stay constant unless one or more factors cause frequencies to change • 5 required conditions: • Random mating • Very large population • No immigration/emigration • No mutations • No natural selection

Process of Speciation • Isolating mechanisms • As new species evolve, populations become isolated • Behavioral Isolation • 2 species capable of mating, but different courtship • Example: Different mating songs in birds • Geographic Isolation • 2 populations separated by geographic barriers • Example: Squirrels around Grand Canyon • One side has gray & other is black • Temporal Isolation • Two or more species breed at different times • Example: Plants releasing pollen on different days

Ch. 17 History of Life • Paleontologists • Scientists who study fossils • Fossil Record • Grouping of organisms based on characteristics • Provides evidence about the history of life on Earth • Shows how different groups have changed over time • Extinction • When species die out • More than 99% of all species are already extinct

Patterns of Evolution • Adaptive Radiation • Process where species evolve into new and divers forms and create new species • Darwin’s finches! • Convergent Evolution • Occurs when two entirely different, unrelated species, develop similar characteristics • Examples: fish, dolphins, sea lions & penguins

Patterns of Evolution Cont. • Coevolution • A process where two species who interact with each other evolve together • Example: Flowers & Pollinators (bees) • Punctuated Equilibrium • Scientists use this to describe patterns of long stable periods interrupted by periods of rapid change in the fossil record • Finches moving from island to island • Trying to fill available niches

Evolution Continued