Disruption of Genetic Equilibrium Section 16-2

Mutation A mutation is a change in the nucleotide- base sequence a DNA molecule.

Population and Gene Movement Gene flow is the movement of alleles into or out of a population. It may take place in two ways: –Immigration the movement of individuals into a population –Emigration the movement of individuals out of a population

Gene Flow

Genetic Drift When allele frequencies in a population change from random events, or chance.

Comparing the Effects of Random and Nonrandom Mating Random mating is mating without caring about phenotypic traits or genetic makeup. Nonrandom mating is driven by choosing mates that have a particular attractive characteristic.

apple maggot flies apples hawthorns Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

If the insect is only attracted to the white flower, then only that flower will reproduce.

Sexual Selection When females tend to choose the males they mate with based on certain traits. Female peacocks seem to prefer extravagant tail feathers.

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

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

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

Formation of Species Section 16-3

Speciation species formation in closely related species Some are very similar to their relatives whereas others look quite different.

Morphological Concept of Species: –Physical characteristics (internal and external) –Limitations: Example: Red tail monkeys have different facial features but are still the same species

The Biological Species Concept Proposed by Ernst Mayr ( ) A species is: –A population of organisms that can successfully interbreed but cannot breed with other groups. Limitations: –Cannot be applied on organisms that are extinct. –Cannot be used for organisms that reproduce asexually.

What is a species? A single kind of organism that is similar in morphology and can interbreed to produce fully fertile offspring.

Geographic Isolation Physical separation of populations due to geographic barriers that prevent interbreeding. Gene flow between the two groups stops Natural selection and genetic drift cause the groups to diverge causing allopatric speciation.

Allopatric Speciation

Allopatric speciation

Reproductive Isolation Genetic barriers that prevent populations found in the same place from breeding. Two types: Prezygotic (premating): prevents fertilization. Postzygotic (postmating): prevents offspring from reproducing.

Prezygotic barrier Prevents reproduction before fertilization.

Isolation occurring after fertilization.

Mule Zorse Liger

Rates of Evolution 1.Punctuated equilibrium is when we see a big change and then no change for a long period of time. Looks like a “stair case”.

2. Gradualism is constant change over a period of time.

References lg.gifhttp:// lg.gif images/California/jackrabbit jpghttp:// images/California/jackrabbit jpg ghttp://a.abcnews.com/images/Politics/pd_polar_bear_080117_ms.jp g jpghttp://english.people.com.cn/mediafile/200802/01/P jpg el/071112/071112_sunbear_hmed_10a.hmedium.jpghttp://msnbcmedia2.msn.com/j/msnbc/Components/Photo_StoryLev el/071112/071112_sunbear_hmed_10a.hmedium.jpg c/teaching/L1/Evolution/l6/grandcanyon.gifhttp://taxonomy.zoology.gla.ac.uk/~rdmp1 c/teaching/L1/Evolution/l6/grandcanyon.gif