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Molecular phylogenies DNA sequence changes to: ATTGCTTTTC Ancestral DNA sequence: ATTGCTATTC Mutations can create synapomorphies Reversal to A at 7th position DNA sequence changes to: ATTGCTTTTC Ancestral DNA sequence: ATTGCTATTC Reversals (‘back mutations’) can remove synapomorphies rodhocetus mesonychid ambulocetus rodhocetus basilosaurus Molecular data used in phylogenetic analysis Immunological distance DNA-DNA hybridization Protein electrophoresis Restriction sites Amino acid sequences DNA sequences Molecular data used in phylogenetic analysis Immunological distance DNA-DNA hybridization Protein electrophoresis Restriction sites Amino acid sequences DNA sequences Molecular data used in phylogenetic analysis Restriction sites Molecular data used in phylogenetic analysis Immunological distance DNA-DNA hybridization Protein electrophoresis Restriction sites Amino acid sequences DNA sequences Tissues from which ancient DNA has been extracted Type of material Mummies Bog bodies Maximum age 5000yrs 7500yrs Feathers Museum skins Naturally preserved skins Bones Amber insects 130yrs 140yrs 10000yrs 25000+yrs ??? Herbaria specimens Charred seeds & cobs Mummified seeds & embryos 118yrs 4500yrs 44600yrs Molecular clocks All phylogenies assume evolutionary differences arise from mutational differences greater mutational differences = greater evolutionary distance Molecular clocks If molecular clock assumptions are true, Phylogeny could be inferred from overall similarity of spp If calibrated, could estimate actual time since taxa diverged Molecular clocks Relative rates Calibrated rates AA changes / 100 codons 70 60 50 40 30 20 10 0 0 100 200 300 400 Time to common ancestor (MYA) 500 Molecular clocks Problems Clock rate differs for different taxonomic groups & nucleotide sequences Differences in DNA repair efficiency Differences in metabolic rates Differences in generation time?
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