Evolution of Populations Chapter 17

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

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

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)

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

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

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

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…

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

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

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

Darwin’s Finches