BSC 196 Lecture 8: Bio- Lecture 8

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8 Feb 2017
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Wednesday, February 8, 2017
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Balancing selection
Balancing selection
- Balancing selection occurs when natural selection maintains stable frequencies of two
or more phenotypes in a population
Heterozygote advantage
Frequency-dependent selection
Heterozygote Advantage
- Heterozygote advantage occurs when heterozygotes have a higher fitness than either
homozygote
Natural selection will tend to maintain two or more alleles at that locus
- allele for sickle-cell hemoglobin (HβS)
hemoglobin: molecule in red blood cells that binds to O2
sickle-cell allele causes cells to sickle
- caused by a single base substitution!
- scale-eating fish (Michio Hori. 1993. Science)
asymmetrical mouth - adaptation for tearing off scales
- Two morphs
dextral (twisted to right)
attack left flank of prey
sinistral (twisted to left)
- attack right flank
prey become more vigilant from attacks from more common morph
- Lake Tanganyika
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