Chapter 16

Section 1

Population genetics – the study of evolution from a genetic point of view

Microevolution – a change in the collective genetic material of a population

Variations in genotype arise in three main waysMutation – a random change in a gene that is

passed on to offspringRecombination – the reshuffling of genes in a

diploid individualRandom pairing of gametes – the union of a

particular pair of gametes is matter of chance

Gene pool – total genetic information available in a populationAllele frequency – number of a certain allele

divided by the total number of alleles of all types in the population

Phenotype frequency - number of individuals with a particular phenotype divided by the total number of individuals in the population

All allele and phenotype frequencies must add up to 1

Genotype frequencies remain the same from generation to generation unless acted on by outside influences

Known as Hardy-Weinberg Genetic Equilibrium, and it is based on a set of assumptions about an ideal hypothetical population that is not evolving

Conditions required for genetic equilibrium:1.No mutations2.Individuals neither enter nor leave the

population3.The population is large4.Individuals mate randomly5.No natural selection

Section 2

Spontaneous mutations occur constantly, at very low rates under normal conditions

If an organism is exposed to mutagens, mutation rates can increase significantly

Mutations can affect genetic equilibrium by producing totally new alleles for a trait

Gene flow – process of genes moving from one population to anotherOccurs through migration of individuals,

dispersal of seeds or spores, etc.

Genetic Drift – phenomenon by which allele frequencies in a population change as a result of random events, or chanceSmall populations usually exhibit a large

degree of genetic driftLarge populations maintain a small degree of

genetic driftFounder effect - occurs when a new colony

is started by a few members of the original population

Mate selection is often influenced by geographic proximity and traits that are similar to their own

Sexual selection is the tendency for females to choose the males they mate with based on certain traits

Stabilizing selection – individuals with the average form of a trait have the highest fitness

Disruptive Selection – individuals with either extreme variation of a trait have greater fitness than individuals with the average form of a trait

Directional Selection – individuals that display a more extreme form of a trait have greater fitness than individuals with an average form of the trait

Section 3

Speciation – the process of species formationResults in closely related species

Morphological Concept of SpeciesSpecies defined primarily according to

structure and appearanceLimitations:

Phenotypic differences among individuals in a single population

Some organisms that appear different enough to belong to different species interbreed

Biological Species ConceptA species is a population of organisms that can

successfully interbreed but cannot breed with other groups

Limitations:Not useful for extinct organisms or for organisms

that do not reproduce sexually

Our modern definition of species includes components of both the morphological and biological species concepts

Speciation begins with isolationIn isolation, two parts of a formerly

interbreeding population stop interbreeding

Physical separation of members of a population

Happens when species arise as a result of geographic isolation

Allopatric Speciation

Results from barriers to successful breeding between population groups in the same areaCaused by:

Disruptive selectionUnrecognized mating

callDifferent times of peak

mating activity

Occurs when two subpopulations become reproductively isolated within the same geographic areaEx: 2 types of insects

that live on different plants in the same area

Sympatric Speciation