Mechanisms of Evolution 15.3

Preview Changes in allele frequencies causes evolution Changes in allele frequencies causes evolution 3 Types of natural selection 3 Types of natural selection How new species form How new species form Speed of Evolution Speed of Evolution Patterns of evolution Patterns of evolution

I. Allele Frequencies A. Review: What is an allele? One form of a gene that causes different traits to appear (Ex: pink, red, or white petals) B. Allelic Frequency- The % of a specific allele in the gene pool. C. Gene Pool- ALL possible alleles in a population

I. Allele Frequencies D. Genetic Equilibrium- A population in which the allelic frequency stays the same 1. Evolution is NOT occurring!!!

II. Genetic Drift A. Genetic Drift- An evolution mechanism in which the allelic frequencies are changed due to chance. 1. Mutations occur by chance, not caused by UV rays, chemicals, radiation, etc.

II. Genetic Drift

2. Greatly affects SMALL populations. a. Ex: Amish populations 1) 30% of settlers carried a recessive allele for extra fingers & toes. 2) Today 1/14 Amish carry the allele compared to 1/1000 non-Amish United States Citizens

III. Natural Selection A. Allele frequencies change because organisms with traits that fit their environment survive and reproduce (others die). B. Affects small AND large populations

III. Natural Selection C. Types of Natural Selection (WHO DOES IT FAVOR???) 1. Stabilizing Selection- Favors average individuals a. Big spiders are seen by birds b. Small spiders can’t find food c. Medium spiders are favored (see graph on pg. 408)

III. Natural Selection 2. Directional selection- Favors ONE extreme for a trait. a. Insects are found deep in a tree trunk. b. Woodpeckers with short & medium length beaks have trouble getting to the insects.c. Long beaks are favored.

III. Natural Selection 3. Disruptive Selection- Favors BOTH extremes, but not intermediate phenotypes. a. A beach has white and dark brown rocks a. A beach has white and dark brown rocks b. White and dark brown snails cannot be seen by birds c. Tan snails can be seen on either color of rock and are eaten Remember the green car?

IV. Speciation A. Species- Group of organisms that look alike, interbreed and produce fertile offspring. B. Speciation- The evolution of new species.

IV. Speciation C. Causes of speciation 1. Geographic Isolation- When a physical barrier divides a population and the two pops evolve differently. a. Different alleles appear in the two populations

IV. Speciation

2. Reproductive Isolation- When closely related organisms can no longer produce fertile offspring. a. Genetic material becomes too different b. Reproductive behaviors become too different

IV. Speciation Rana boylii Breeds late March to May Rana aurora Breeds January to March

IV. Speciation 3. Change in Chromosome # a. Polyploid- Individual or species with more than the normal set of chromosome (3n, 4n, 5n etc) b. Caused by mistakes in meiosis

IV. Speciation c. Organisms with different # of chromosomes cannot produce fertile offspring d. Polyploids CAN interbreed among themselves if they have the same # of chromosomes

IV. Speciation D. Speciation Rates 1. Gradualism- Evolution occurs at slow, steady rate 2. Punctuated Equilibrium- Evolution occurs in short bursts with long periods of equilibrium in between. (See Elephants on pg. 411)

IV. Speciation 3. Both gradualism and punctuated equilibrium are accepted today. 4. Side Note: Phylogenic Tree

V. Patterns of Evolution A. Adaptive Radiation- One species evolves into an array species to fit different niches (mini habitats) 1. Diversity allows for more flexibility and larger numbers 2. Supports the idea of natural selection

V. Patterns of Evolution

B. Divergent Evolution- Similar species become increasingly different. C. Convergent Evolution- Very distantly related organisms become more similar 1. They share similar environments and selection pressures

Recap A. Changes in allele frequencies causes evolution B. 3 Types of natural selection 1. Stabilizing 2. Directional 3. Disruptive

Recap C. Speed of evolution 1. Gradualism 2. Punctuate equilibrium

Recap D. How new species form 1. Geographic Isolation 2. Reproductive Isolation 3. Changes is chromosome # E. Patterns of evolution 1. Adaptive Radiation 2. Divergent Evolution 3. Convergent Evolution