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BS 162 Sept 13.docx

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Biological Science
BS 162

Exam 1 – 1, 25, 22, 24( minus hardy-weinburg equilibrium) Figure 2.3-1.3  Role of Natural Selection o All or none phenomenom o Gradual changes in nos  NS affects distribution of indiv in a a pop o Stabilizing o Disruptive o Sexual  Intrasexual-indovidials of one sex of a specis compete with one another to mate with indiv of the other sex of the same species  Intersexual- individuals of one sex serve as the selection pressure on individuals of the other sex of the same species  Ex. Cardinal bird species- the female selects the male that she wants to be with; studies have shown that this is based on the males red feathers, song, and territory  Sexual dimorphism-when the female or the male is dramatically different from the other sex of that species o Directional  Balanced polymorphism: phenotypes(characteristics) are maintained in fairly stable proportions o Cepea-united kingdom; bird predators; variation in shell color like light to dark, no bands up through 5 bands; o Light environment-birds pray on dark banded individuals so their genes are being removed from the population you would think but the dark banded individuals occur in a similar portion percentage in the next generation o Dark environment- light individuals are being removed by birds so you would think genes are being removed but similar portion percentage is present in next generation  Possible explanation may be that many alleles are present in the determination of color of shells  NS may result in adaptation sof pops of orgs to physical environment o Cline: graded variation in a trait(s) that follows geographic distribution  Ex. Yarrow plants in sierra Nevada: higher the altitude smaller the plant
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