- Slides: 12
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