1. Evolution of Populations
Chapter 17

2. 17-1 Genes and Variation
Species-group of organisms that can reproduce and make fertile offspring
Example: red winged blackbird
Population- group of the same species living in the a given area

3. Variation and Gene Pools
Genes-sequence of DNA that codes for certain traits
Alleles- variations of a gene or trait
Example: brown vs. black fur in mice
Gene pool- all the genes including alleles within a population
Example? All the brown and black fur mice in a population
Relative frequency- the number of times an allele exists in a gene pool

4. 3 Sources of Genetic Variation
1. Mutation- any change in a DNA sequence *sexual reproduction
2. Genetic Recombination in Sexual Reproduction- movement of chromosomes during gamete formation in meiosis and crossing over *sexual reproduction
3. Lateral Gene Transfer-passing of genes from one individual to another
True or False? The number of phenotypes produced for a given trait depends on how many genes control the trait (single gene trait/ polygenic trait)

5. Single Gene & Polygenic Traits
The # of phenotypes produced for a trait depends on how many genes control it.
Single gene trait- trait controlled by one gene
Examples?
Polygenic trait- trait controlled by many genes

6. 17-2 Evolution as Genetic Change
* Natural selection on single gene traits can change allele frequencies resulting in evolution.
*Natural selection can affect the distribution of phenotypes in 3 ways: directional selection, stabilizing selection, disruptive selection
*Hardy Weinberg Principle-allele frequency in a population will remain constant unless something causes it to change

7. 5 Conditions that would Maintain Genetic Equilibrium
where allele frequencies remain constant
1. Random mating-
where all individuals have an equal amount of mating, leading to equal chance of alleles being passed on
2. large population-
where genetic drift would have little affect on populations
3. no movement in or out of population-
individuals do not leave or enter a population

8. 5 conditions continued…
4. no mutations-
if mutations occur that would introduce new alleles into the population
5. no natural selection-
Where all genotypes have an equal chance at survival and reproduction
*If these conditions are not met, genetic equilibrium will be disrupted, and the population will evolve.
In other words…

9. 17-3 The Process of Speciation
Speciation-changes that lead to the formation of new species
Reproductive isolation- as new species evolve, populations become reproductively isolated from each other
1. Behavioral Isolation- when 2 species are capable of interbreeding but don’t b/c of behavioral differences
2. Geographic Isolation- populations are separated by geographic barriers inhibit interbreeding
3. Temporal Isolation- when breeding times are different, therefore not interbreeding

10. 17-4 Molecular Evolution Molecular Clock
Uses mutation rates in DNA to estimate the time that 2 species have been evolving independently
Used to compare pieces of DNA marking the evolutionaary time

11. Darwin’s Finches finches descended from a common ancestor;
natural selection drove different beak shapes as the populations adapted
to environment
(different food
sources)

12. Darwin’s Finches