Chapter 17

Population Genetics and Speciation

• Population genetics – the study of the frequency and interaction of alleles and genes in populations.

*Microevolution can be studied by observing changes in the numbers and types of alleles in populations.

• Normal distribution – a line graph showing the general trends in a set of data of which most values are near the mean.– *Biologists study polygenic phenotypes by

measuring each individual in the population and then analyzing the distribution of the measurements.

• **Genetic variation and change are measured in terms of the frequency of alleles in the gene pool of a population.

• ***The major source of new alleles in a natural population is mutation in germ cells. (The sperm and ova)

• Genetic equilibrium – a state in which the allele frequencies of a population remain in the same ratios from one generation to the next.

Forces of genetic change:

• 1.  Gene flow

• 2.  Nonrandom mating

• 3.  Genetic drift

• 4.  Mutation

• 5.  Natural selection

• *Sexual reproduction creates the possibility that mating pattern or behaviors can influence the gene pool of a population.

• **Allele frequencies are more likely to remain stable in large populations than in small populations.

Forming New Species

** Speciation has occurred when the net effects of evolutionary forces result in a population that has unique features and is reproductively isolated.

• Reproductive isolation – a state in which a population can no longer interbreed with other populations to produce future generations.

• Subspecies – a taxonomic classification below the level of species; refers to populations that differ from, but can interbreed with, other populations of the same species.

Mechanisms of Isolation• Geography

– A physical barrier• Ecological Niche

– Role the species has in the environment• Mating Behavior and Timing

– Patterns, sounds, actions, etc.• Polyploidy

– Cannot pair gametes due to having an extra pair.• Hybridization

– When two closely related species have offspring.– Often times the offspring are sterile

– Example = mule (offspring of a donkey and horse)

Extinction

• Occurs when a species fails to produce any more descendents.

****The species that exist at any time are the net result of both speciation and extinction.

-if you think of speciation as like a branch off of a family tree, then extinction is like the loss of one of those branches.

Assignment

• Pg. 417: 7-11

• Pg 418: 19-20

• Pg. 419: 1-9

• Due on Monday