1 / 7

IV. Evolution as Genetic Change

IV. Evolution as Genetic Change. *Populations can evolve over time in different situations. A. Natural Selection on Single-Gene Traits -Natural Selection on single-gene traits can lead to changes in allele frequencies & thus to evolution. Example : Brown vs. Black vs. Red

rlindley
Download Presentation

IV. Evolution as Genetic Change

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. IV. Evolution as Genetic Change *Populations can evolve over time in different situations. A. Natural Selection on Single-Gene Traits -Natural Selection on single-gene traits can lead to changes in allele frequencies & thus to evolution. Example : Brown vs. Black vs. Red lizards. If brown is less visible, red & black may be eaten by predators.

  2. B. Natural Selection & Polygenic Traits -When dealing with a range of phenotypes, a bell curve is used for comparison. -Natural selection can affect the distribution of phenotypes in any of three ways : 1. Directional selection 2. Stabilizing selection 3. Disruptive selection

  3. Directional Selection Directional selection – when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. -The range of phenotypes shifts as some individuals die & others succeed, ex: Darwin’s finches & increase in large seed availability.

  4. Stabilizing Selection Stabilizing selection – when individuals near the center of the curve have higher fitness than individuals at either end of the curve. -The center of the curve stays at its current position, but narrows the overall graph, ex: human birth weight.

  5. Disruptive Selection Disruptive selection – when individuals at the upper & lower ends of the curve have higher fitness than individuals near the middle. -Selection acts most strongly against individuals of an intermediate type. -In disruptive selection, the pressure of natural selection can become strong enough to split a single curve in two, creating two distinct phenotypes, ex : Darwin’s finches & availability of large & small seeds only.

  6. C. Genetic Drift Genetic drift – random change in allele frequencies that occurs in small populations. -In small populations, some individuals with particular traits may leave more descendants than others by chance. -Over time, a series of chance occurrences of this type can cause an allele to become common in a population. -Can occur when a small group colonizes a new habitat. Founder effect – change in allele frequencies as a result of the migration of a small subgroup of a population.

  7. D. Evolution vs. Genetic Equilibrium *To understand how evolutionary change works, we must consider if there are any situations in which evolution doesn’t happen. Hardy-Weinberg principle – principle that states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. Genetic Equilibrium – situation in which allele frequencies remain constant. *No allele change = no evolution. -In order to maintain genetic equilibrium 5 conditions must be kept : 1. Random mating- no choosing mates. 2. Large population – no genetic drift. 3. No moving into/out of population. 4. No mutations. 5. No natural selection.

More Related