Evolution of Populations
Chapter 17Evolution of Populations17-1 Genes and Variation
Species-group of organisms that can reproduce and make fertile
offspringExample: red winged blackbirdPopulation- 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 traitExample: brown vs. black
fur in mice
Gene pool- all the genes including alleles within a
populationExample? All the brown and black fur mice in a
population
Relative frequency- the number of times an allele exists in a
gene pool3 Sources of Genetic Variation
1. Mutation- any change in a DNA sequence *sexual reproduction2.
Genetic Recombination in Sexual Reproduction- movement of
chromosomes during gamete formation in meiosis and crossing over
*sexual reproduction3. Lateral Gene Transfer-passing of genes from
one individual to anotherTrue 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 TraitsThe # of phenotypes produced
for a trait depends on how many genes control it.Single gene trait-
trait controlled by one geneExamples?Polygenic trait- trait
controlled by many genesExamples?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
Genetic equilibrium-where allele frequencies remain constant1.
Random mating-where all individuals have an equal amount of mating,
leading to equal chance of alleles being passed on2. large
population- where genetic drift would have little affect on
populations3. no movement in or out of population- individuals do
not leave or enter a population
5 conditions continued4. no mutations-if mutations occur that
would introduce new alleles into the population5. 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
speciesReproductive isolation- as new species evolve, populations
become reproductively isolated from each other1. Behavioral
Isolation- when 2 species are capable of interbreeding but dont b/c
of behavioral differences2. Geographic Isolation- populations are
separated by geographic barriers inhibit interbreeding3. Temporal
Isolation- when breeding times are different, therefore not
interbreeding
17-4 Molecular EvolutionMolecular ClockUses mutation rates in
DNA to estimate the time that 2 species have been evolving
independentlyUsed to compare pieces of DNA marking the
evolutionaary time
Darwins Finchesfinches descended from a common ancestor;natural
selection drove different beak shapes as the populations adaptedto
environment (different food sources)
Darwins Finches
