Outcomes of Natural Selection (Chapter 19) by po2378


									Outcomes of Natural Selection
 (Chapter 19 and part of 20)
Small Steps or Great Leaps? See Fig. 20.20 in text
punctuated equilibrium site
• Microevolution (IB)
• Macroevolution (IB) –
The Effects of Selection on Populations
(Fig. 19-3 in text)

1.   Stabilizing selection
2. Directional Selection
3.Disruptive Selection
Animation of Selections
 Random Changes in Frequencies
• a change in allele frequency in a population due
  simply to chance is called genetic drift
• Processes leading to genetic drift:
   1. population bottleneck –
2. founder effect –
   • Afrikaaners of South Africa in text
     – In the 1680s Ariaantje and Gerrit Jansz emigrated from
       Holland to South Africa, one of them bringing along an allele
       for the mild metabolic disease porphyria. Today more than
       30000 South Africans carry this allele and, in every case
       examined, can trace it back to this couple — a remarkable
       example of the founder effect.

  • Amish in Pennsylvania
     – Eastern Pennsylvania is home to beautiful farmlands and
       countryside, but it's also a gold mine of information for
       geneticists, who have studied the region's Amish culture for
       decades. Because of their closed population stemming from a
       small number of German immigrants -- about 200 individuals -
       - the Amish carry unusual concentrations of gene mutations
       that cause a number of otherwise rare inherited disorders,
       including forms of dwarfism and plolydactyly.

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