BIOL 2P02 Lecture Notes - Lecture 12: Sickle-Cell Disease, Allele Frequency, Macroevolution

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Four main mechanisms cause allele frequency change: mutation, genetic drift, natural selection and gene flow. The primitive earth was hot and steamy with small, warm oceans no free oxygen! Life at the beginning is anaerobic (not oxygen needing) only bacteria. Age of the bacteria: prokaryotes dominated the earth for most of its history, bacteria can live under much wider bacteria can live under a much wider variety of conditions than eukaryotes. The onset of oxygen: the atmosphere of the primitive earth was probably like that of mars today: no free oxygen, oxygen comes from photosynthesis. The electrons take hydrogen with them, leaving oxygen gas. Rise of the eukaryotes: eventually the proterozoic era was dominated by small soft- bodied cells than had a nucleus, there were the eukaryotes, some were unicellular, others multicellular ago, first fossil evidence 2. 1 billion years. Ediacaran life: the earliest known complex multicellular organisms, a period late in the proterozoic era.

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