BIS 2B Lecture 14: Natural Selection and Genetics

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10/26 Natural Selection and Genetics
Midterm #2 = November 14
- content: 10/15 Lecture 9 - 11/9 lecture 20, plus all the discussion in between
- problem sets for mendelian and pop. genetics going up this weekend
- Halloween = if discussion can be recorded, there will be no class at class time; content
will still be included in midterm
Types of natural selection:
1. stabilizing selection = the average/middle is favored; the extremes are no good;
decrease variability
2. directional = phenotype frequency is driven to one of the extremes rather than the other
extreme, much less the average
3. disruptive/diversifying = the extremes are better than the average/middle; increase
variability
a. 1-3 was lecture 9
b. ex: seed size and bird bill size
4. balancing
5. frequency-dependent
6. kin selection (and the evolution of cooperation)
7. sexual
Case Study
- 1898 Hermon Carey Bumpus: after a storm, 64 English sparrows died, 72 lived
- measured length of birds who lived and died = smaller survived
- storm that equally affects everything on population = hard selection event
- for nat select to be true: differential variation, offspring has to be small like their parents,
genotypes must be heritable
Balancing Selection
- suggests that heterozygous state of single gene trait is selected for
- case study = Warfarin resistance in Norway rates
- Warfarin = blood thinner, too much causes ulceration and bleed to death
- prevents vitamin K from complexing with coagulants in blood to stop bleeding
- rat poison
- but in 1959 warfarin-resistant rats strated to rise
- resistance conferred by single mutation at W locus: Ws ⇒ Wr
- at least one Wr in alleles makes for resistant rats
- why didnt warfarin resistance allele (Wr) go to fixation? ⇒ WrWs heterozygotes have
higher fitness than either homozygote
- rats need vitamin K, it's almost limiting
- allele that confers warfarin resistance also makes in difficult to absorb dietary vita
K
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Document Summary

Midterm #2 = november 14 content: 10/15 lecture 9 - 11/9 lecture 20, plus all the discussion in between. Problem sets for mendelian and pop. genetics going up this weekend. Halloween = if discussion can be recorded, there will be no class at class time; content will still be included in midterm. 1898 hermon carey bumpus: after a storm, 64 english sparrows died, 72 lived. Balancing selection suggests that heterozygous state of single gene trait is selected for case study = warfarin resistance in norway rates. Warfarin = blood thinner, too much causes ulceration and bleed to death. Prevents vitamin k from complexing with coagulants in blood to stop bleeding. But in 1959 warfarin-resistant rats strated to rise rat poison resistance conferred by single mutation at w locus: ws wr. At least one wr in alleles makes for resistant rats. Wrws heterozygotes have higher fitness than either homozygote rats need vitamin k, it"s almost limiting.

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