1 / 10

Types of Natural Selection

Types of Natural Selection. SBI3U. Sickle-Cell Anemia. Mutation + genetic variation + natural selection = evolution of a population Sickle- cell allele resulted from a single base mutation in the DNA coding for hemoglobin

halima
Télécharger la présentation

Types of Natural Selection

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. Types of Natural Selection SBI3U

  2. Sickle-Cell Anemia • Mutation + genetic variation + natural selection = evolution of a population • Sickle- cell allele resulted from a single base mutation in the DNA coding for hemoglobin • Heterozygous individuals, Ss, are resistant to malaria  better chance of survival • Sub-Sahara Africa- if you carry the allele, S, than you will survive to reproduce, and pass on the allele to the next generation • Therefore, an increase in the frequency of the allele

  3. Directional Selection • Occurs when selection favours an increase or decrease in the value of a trait from the current population average. • Favours individuals with a more extreme variation of a trait • Results in a shift away the average condition • Read Hummingbird example on the bottom of pg. 326

  4. Directional Selection Example • -The soil in the original environment was a medium brown • - After a volcano the soil becomes darker • Mouse population evolved to blend in with the darker surroundings • Therefore, environment favoured individuals with more extreme variations of the trait

  5. Stabilizing Selection • Selection against individuals exhibiting traits that deviate from the current population The average phenotype within a population is favoured by the environment • Read the human birth weight example on the bottom of page 327.

  6. Stabilizing Selection Example • The soil remains medium brown • Medium brown mice survive from predation • Medium brown mice pass of their allele for medium brown fur to their offspring • Light/ dark brown mice are eaten more -> those alleles are not passed on

  7. Disruptive Selection • Selection that favours two or more variations of a trait that differ from the current population average. • Favours opposite extremes of a trait over individuals with intermediate variations

  8. Disruptive Selection Example • Mouse move to a new environment with light brown rock and dark brown volcanic rock • Light brown and dark brown mice blend in with their environment, but medium brown mice do not • Medium brown mice are eaten by predators • Light/ dark brown mice pass on their genes to future generations

  9. Hardy- Weinberg Equilibrium • If allele frequencies change over time, the population is NOT in Hardy-Weinberg Equilibrium • Therefore, a ‘disturbing factor’ is acting on the population • Natural Selection • Small population size • Mutation • Immigration/ Emigration • Sexual selection

More Related