Put your homework out on your desk.. I am going to check it! Biology March 20, 2013 Bellringer: --Grab the notes sheet… THEN Look at your list of adaptations from Build-A-Beast. Identify one of each that you used: Chemical- Physical- Behavioral- Objectives: Population Evolution Notes QUIZ FRIDAY!!! HW: Analyze populations… Over… Notes Monday, reading last night, Notes Today! TEST TUESDAY!!! You will get a review sheet tomorrow! Put your homework out on your desk.. I am going to check it!

Evolution of Populations

A group of individuals of the same species living in the same area. Population A group of individuals of the same species living in the same area.

Species Group of similar organisms that can breed and produce fertile offspring

Speciation Process by which a new species is formed How does Speciation occur?

The combined genetic information of all of the members of a population Gene Pool The combined genetic information of all of the members of a population

GENETIC DRIFT PROCESS IN WHICH GENE FREQUENCIES WITHIN A POPULATION CAN CHANGE BY CHANCE – NATURAL SELECTION NOT INVOLVED.

GENETIC DRIFT CHANCE OCCURRANCES INCLUDE : - 1 INDIVIDUAL PRODUCES MORE OFFSPRING THAN OTHERS JUST BY CHANCE - PART OF A POPULATION IS DESTROYED IN A DISASTER (EARTHQUAKE, FLOOD, ETC) - EXAMPLE - NORTHERN ELEPHANT SEAL 1890 POPULATON < 20 DUE TO HUNTING. THE SURVIVORS WERE JUST THE LUCKY ONES.

The Bottleneck Effect Population bottlenecks occur when a population’s size is reduced for at least one generation. Can reduce genetic variation very quickly, even if only for one generation!

Founder’s Effect A founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have: reduced genetic variation from the original population. a non-random sample of the genes in the original population.

GENE FLOW Migration THE EXCHANGE OF GENES BETWEEN 2 OR MORE POPULATIONS THE GREATER THE GENE FLOW, THE LESSER THE GENETIC DIFFERENCES BETWEEN THE POPULATIONS THE LESSER THE GENE FLOW, THE GREATER THE DIFFERENCES.

Sources of Genetic Variation Mutation Gene Shuffling

A change in the DNA of an organism Mutation A change in the DNA of an organism

Mutation Might affect the phenotype of the organism Might affect the organism’s ability to survive and reproduce (fitness)

Gene Shuffling Rearranging of genes during reproduction Occurs in organisms that reproduce Sexually

Gene Shuffling cont. In humans, gamete formation can result in 8.4 million different gene combinations.

Natural Selection acts on Phenotypes! Natural Selection determines which genes will be passed on to the next generation

Natural Selection can affect the genotype and phenotype of a population

Natural Selection and Phenotype Natural Selection can affect the distribution of phenotypes in 3 ways: Directional Selection Stabilizing Selection Disruptive Selection

Directional Selection Individuals at one end of curve have an advantage (more fit). Over time, the curve will move in one direction.

Disruptive Selection Individuals at the upper and lower end of the curve have an advantage (more fit) Eventually, the curve splits into both directions

Stabilizing Selection Individuals in the middle of the curve have an advantage The curve stays narrow and in the same place