Mechanisms of Natural Selection and Evolution

April 20, 2017 Objective: Agenda: Students will able to identify different aspects of natural selection Agenda: Notes Video/illustration Finish project

Natural Selection Review Four parts of Natural Selection include: 1. Overproduction of Offspring 2. Genetic Variation***MUST BE PRESENT*** 3. Struggle to Survive 4. Successful Reproduction

Natural Selection influences genetics If an allele is responsible for a beneficial trait, the frequency of the allele will increase with time as a result of natural selection. Multiple types of selection: Directional Selection – when multiple variations of a trait exist, the environment selects for one of the “extremes” of the trait Stabilizing Selection – when multiple variations of a trait exist, the environment selects for the “middle” trait EXAMPLE: Giraffe necks Directional: selecting for long necks over time Stabilizing: selecting for medium length necks

How does Evolution work? Evolution is governed by the principles of genetics It is a change in successive generations of organisms, due to: random mutation Adaptation Natural selection Extinction

MUTATIONS Genetic mutations and variety produced by sexual reproduction allow for diversity within a given population.

A mutation may result in change that is: 1. Favorable: improves a species’ ability to exist in its environments.

2. Unfavorable: does not improve a species’ ability to exist in its environment. Mutations can also be neutral.

Adaptation Adaptations are structures, functions, or behaviors that enable a species to survive. Generally evolve over LONG periods of time – could be millions of years.

Natural Selection the survival and reproduction of the individuals in a population that exhibit the traits that best enable them to survive in their environment. The Survival of the Fittest

Extinction Extinction occurs when an ENTIRE species dies off. Extinction often occurs as a result of the lack of variation in the genetics of a population.

Artificial Selection When humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment This is called “artificial selection” Example of artificial selection in plants: five vegetables derived from wild mustard

Artificial Selection in Animals: Dog Breeding German shepherd Yorkshire terrier English springer spaniel Mini-dachshund Golden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog

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