AS Biology Handwritten Notes 2015
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#141 Evolution and Extinction
General theory of evolution : organisms have changed over time. Molecular comparison between species 1. Comparing amino acid sequences of proteins Number of difference in the nucleotide sequences measure how closely related the species are. 2. Comparing nucleotide sequences of mitochondrial DNA Human mtDNA : inherited through the female line zygote contains the mitochondria of the ovum mtDNA is circular so can't undergo any form of crossing over, changes in nucleotide sequence can only arise by mutation Different human populations show differences in mitochondrial DNA sequences. This provides evidence for the origin of different populations --> ' molecular clock ' hypothesis: there is a constant rate of mutation over time the greater the number of differences in the sequence of nucleotides, the longer ago those individuals shared a common ancestor 'clock' can be estimated from fossil evidence Extinction Species can become extinct through a variety of mechani...
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