Name Period Date Unit 3.4 Mechanisms of Evolution Notes Outline Learning Objectives: discuss patterns observed in evolution. Describe factors that influence speciation. Compare gradualism with punctuated equilibrium. I. Mechanisms of Evolution Darwin s theory of natural selection remains the central theme of. Scientists of today know that: Evolution occurs at the level, with as the raw material. A. Population Genetics 1. Hardy-Weinberg Principle states that when allelic frequencies remain constant, a population is in genetic. Even though the number of owls doubled, the of gray to red owls remained the same. 2. p 2 + 2pq + q 2 = 1 This equation allow us to determine the of each in the population. (1) homozygous dominant: (2) heterozygous: (3) homozygous recessive: (4) Note: the sum of these frequencies equals. 3. A population in genetic equilibrium must meet all of the following conditions: The population is very b) No or c) Mating is d) do not occur (no new variations) e) does not occur
B. Genetic Drift is a change in the allelic frequencies in a population that is: In and the chance of losing an populations the effects of genetic drift become more pronounced, becomes greater. 1. Founder Effect occurs when a small sample of a population settles in a location from the rest of the. alleles that were in the original population might be in the new population. 2. Bottleneck occurs when a population to a very low number and then. Can genetic C. Gene Flow 1. No new genes the population and no genes the population. 2. A population in experiences no gene flow, however, few populations are. 3. movement of individuals between populations differences between populations. D. Nonrandom Mating 1. Rarely is mating completely in a population. 2. Usually individuals mate with individuals in close. 3. This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are for particular traits. 2
E. Mutation 1. A mutation is a in genetic material 2. Occasionally mutations provide an in subsequent generations. to organisms and become more 3. Basis upon which works. F. Natural Selection Select the individuals that are best adapted for 1. and. Selection eliminate extreme expressions 2. Selection increases the expression of the extreme version of a trait 3. Selection splits a population into two groups 4. brown skin if live in grassy area, grey skin if live on rocky island shore. Selection operates in populations where males and females differ significantly in appearance. males are b) more likely reproductive success and in the group yet bodies are still enhanced for (1) Examples: 3
II. Reproductive Isolation A. Prezygotic Isolation: 1. Eastern and Western meadowlarks are similar in appearance but their mating songs separate them. B. Postzygotic Isolation occurs when but a hybrid offspring cannot or. 1. A liger is the offspring of a male lion and a female tiger. Ligers are. III. Speciation For speciation to occur, a population must. and then be reproductively A. Allopatric Speciation: a barrier divides one population into two or more populations. 1. example squirrels in the Grand Canyon B. Sympatric Speciation: species evolve into a new species a physical barrier 1. example apple maggot flies lay eggs on apples or hawthorns depending on the type of fruit they grew up on. IV. Patterns of Evolution A. Adaptive Radiation aka Divergent Evolution 1. Can occur in a relatively time when species gives rise to different species in response to the creation of or some other ecological opportunity. B. Coevolution follows large scale events b) Cichlid fish of Lake Victoria in Africa 1. The relationship between two species might be so close that: occurs when two species benefit each other. b) comet orchids and moths that pollinate them. 4
2. Coevolutionary arms race one species can evolve a dependency on another species. a plant and an insect that is dependent on the plant for food (1) the plant evolves a defense (2) The insects evolve the to resist the defense. (3) The response continues to escalate C. Convergent Evolution 1. species evolve similar traits even though they live: 2. Occurs in environments that are geographically far apart but have similar: D. Rate of Speciation 1. Punctuated Equilibrium explains spurts of genetic change causing species to diverge. These periods punctuate much longer periods when the species exhibit little change. 2. Gradualism evolution proceeds in, steps 5