1 / 10

Mechanisms for Evolution

Mechanisms for Evolution. Natural selection traits that improve survival or reproduction accumulate in the population ADAPTIVE change Genetic drift frequency of traits changes in a population due to chance events RANDOM change. Natural Selection.

eunice
Download Presentation

Mechanisms for Evolution

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mechanisms for Evolution • Natural selection • traits that improve survival or reproduction accumulate in the population • ADAPTIVE change • Genetic drift • frequency of traits changes in a population due to chance events • RANDOM change

  2. Natural Selection • Selection acts on any trait that affects survival or reproduction • predation selection (speed, camouflage, defenses) • physiological selection (disease resistance, protection from injury) • sexual selection (attractiveness, fertility)

  3. Modes of Selection Directional: Darker mice are favored because they live in dark rocks. Disruptive: Intermediate color at a disadvantage. Mice live in both light and dark rocks. Stabilizing: Intermediate color is advantaged, extremes are not favored.

  4. Genetic Drift • Chance events change frequency of traits in a population • not adaptation to environmental conditions • Founder effect • Bottleneck

  5. CWCW CRCR CRCR CRCR CRCR CRCR CRCW CRCR CRCW Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring CRCR CRCR CWCW CRCR CWCW CRCR CRCW CRCW CRCR CRCR CRCR CWCW CRCR CRCW CRCR CRCR CRCR CRCR CRCW CRCW CRCW Generation 2 p = 0.5 q = 0.5 Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Generation 3 p = 1.0 q = 0.0  Genetic drift (can greatly affect small populations)

  6. albino deer Seneca Army Depot Founder effect (Genetic drift) • A new population is started by a small group of individuals or are isolated from other population • just by chance somerare traits may be at high frequency; others may be missing • skews the gene pool of new population • less genetic diversity

  7. Example: Distribution of blood types • Distribution of the O type blood allele in native populations of the world reflects original settlement

  8. Bottleneck effect (genetic drift) • A large population drastically reduced by a disaster • famine, natural disaster, loss of habitat… • loss of variation by chance event • narrows the gene pool

  9. Example: Cheetahs • All cheetahs share a small number of alleles • less than 1% diversity • as if all cheetahs are identical twins • 2 bottlenecks • 10,000 years ago • Ice Age • last 100 years • poaching & loss of habitat

  10. Question??? • What do you think is the definition of a species? • Pair up and write down your definition of a species and how do we get new species?

More Related