3. Genetic Drift The change in allele frequencies as a result of chance processes. Directly related to the population numbers. These changes are much more pronounced in small populations. Smaller population sizes are more susceptible to genetic drift than larger populations because there is a greater chance that a rare allele will be lost.

Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.

In a population of 100 bears, suppose there are two alleles for fur color: A1 (black) and A2 (brown). A1 has a frequency of .9, A2 a frequency of .1 (1.0 = 100%). The number of individuals carrying A2 is very small compared to the number of individuals carrying A1, and if only fifty percent of the population survives to breed that year, there's a good chance that the A2s will be wiped out.

Examples of Genetic Drift The Founder Effect: A founder effect occurs when a new colony is started by a few members of original population. Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived. Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals.

E.g., the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.

Ellis - van Creveld Syndrome

Bottleneck = any kind of event that reduces the population significantly..... earthquake....flood..... disease.....etc.…

E.g. bottleneck: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000 but their genes still carry the marks of this bottleneck. They have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

4. Mutations Are inheritable changes in the genotype. Provide the variation that can be acted upon by natural selection. Mutations provide the raw material on which natural selection can act. Only source of additional genetic material and new alleles. Can be neutral, harmful or beneficial( give an individual a better chance for survival). Antibiotic resistance in bacteria is one form.

Mutation is a change in DNA the hereditary material of life Mutation is a change in DNA the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology—all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life. Somatic mutations occur in non-reproductive cells and won’t be passed onto offspring.

The only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations. A single germ line mutation can have a range of effects: No change occurs in phenotype.

2. Small change occurs in phenotype. 3. Big change occurs in phenotype. Some really important phenotypic changes, like DDT resistance in insects are sometimes caused by single mutations1. A single mutation can also have strong negative effects for the organism. Mutations that cause the death of an organism are called lethal — and it doesn't get more negative than that.

Causes of Mutations DNA fails to copy accurately. External influences can create mutations. Mutations can also be caused by exposure to specific chemicals or radiation.

5. Non-Random Mating In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behavior. Many plants self-pollinate, which is also a form of non-random mating (inbreeding).

Sexual reproduction results in variation of traits in offspring as a result of crossing over in meiosis and mutations Genetic shuffling is a source of variation.

Sexual selection occurs when certain traits increase mating success.

There are two types of sexual selection. intrasexual selection: competition among males intersexual selection: males display certain traits to females