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Population Genetics and Speciation: Understanding Genetic Variation and Evolutionary Forces

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  1. Chapter 17 Population Genetics and Speciation

  2. 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.

  3. 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.

  4. **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)

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

  6. Forces of genetic change: • 1.  Gene flow • 2.  Nonrandom mating • 3.  Genetic drift • 4.  Mutation • 5.  Natural selection

  7. *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.

  8. 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.

  9. 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.

  10. 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)

  11. 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.

  12. Assignment • Pg. 417: 7-11 • Pg 418: 19-20 • Pg. 419: 1-9 • Due on Monday

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