Chapter 16-1 Genetic Equilibrium

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Population Genetics The study of evolution from a genetic point of view.

Bell Curve

Natural Selection acts on Variations Quantitative traits, such as height and weight, tend to follow a bell shaped curve.

Examples of Bell Curves

Variations in a Population A. Some variations are influenced by environmental factors, such as the amount of food or quality of food available to an organism. B. Variations are also influenced by heredity. What Variations do you see in our classroom population???

Variation in Genes A.Mutation- a random change in a gene that is passed on to offspring. B. Recombination- the reshuffling of genes in a diploid individual (meiosis; independent assortment crossing over) C. The random pairing of gametes during sexual reproduction.

Gene Pool The total genetic information in a population. (the genes for the next generation exist in an imaginary pool)

Allelic Frequency The percentage of any specific allele in the gene pool Genetic Equilibrium A population in which the allele frequencies stay the same

Population A population consists of a group of individuals of the same species that routinely interbreed. Population of Giraffes in Calauit in the Philippines

Populations and Evolution Populations are important in the study of evolution because a population is the smallest unit in which evolution occurs Populations evolve, not individuals!!!

Microevolution A change in the collective genetic material of a population. (genetic material= the many alleles or variations of the many genes that code for various traits)

How can a population’s gene pool change over time? When a population is not in genetic equilibrium….

16.2 Disruptions in Genetic Equilibrium 1. Mutations 2. Genetic Drift in Small populations 3. Gene Flow –Immigration- the movement of individuals into a population. –Emigration- the movement of individuals out of a population. 4. Non-random mating 5. Natural Selection

Genetic Drift Genetic drift is the phenomenon by which allele frequencies in a population change as a result of random events, or chance. e.g. Northern elephant seals have lost genetic variability because they have been hunted to near extinction. With such a small population left and a small gene pool  less variation.

Genetic Bottleneck Occurs when environmental disturbances cause populations to become so small that inbreeding occurs. –leads to decreased genetic variability. –Over evolutionary time, populations with low variability are less likely to adapt to changing environmental conditions. e.g. Cheetahs and black footed ferrets.

3 Different Types of Selection Stabilizing Directional Disruptive

Stabilizing Selection Individuals with the average form of the trait have the highest fitness

Directional Selection Individuals that display one of the extreme forms of trait have greater fitness than individuals with an average form of the trait.

Disruptive Selection Individuals with either extreme of a trait have greater fitness than the average form of the trait

Journal: If the largest and smallest organisms in a population have more success in their ability to reproduce, this might lead to what type of selection?

16.3 Speciation The process of species formation which results in closely related species.

What can cause speciation? Geographic Isolation Reproductive Isolation

Cause of Speciation Geographical Isolation: the physical separation of members of a population. e.g. Death Valley pupfish Grand Canyon squirrels

Cause of Speciation Reproductive Isolation: results from barriers to successful breeding between population groups in the same area. e.g. Frogs

The Rates of Speciation Gradualism Punctuated Equilibrium

The End