BSCI 207 Lecture Notes - Lecture 3: Nuclear Dna, Ribosomal Rna, Eukaryote
5 Oct 2016
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Morphological traits can"t be used to infer genetic relatedness. Cannot be used to infer primitive organisms; more information is needed (fossils, etc. Sequences are used: dna, rna, amino acid sequences, these sequences are compared. More similarities = more recently two taxa had a common ancestor: uses similarities between sequences. How do you decide which sequence to use: rate of change of sequences. Recently diverged = sequence that changes fast. Repetitive sequences mutate easily: dna polymerase slips . Mtdna > nuclear dna: mutates quickly due to the way it replicates, mtdna is single stranded for a long time during replication. Introns > exons: introns are not highly selected, therefore mutates faster than coding sections. 3rd positions of codons > 1st or 2nd positions: 3rd position often does not affect protein sequence and therefore mutates faster than 1st or 2nd positions. Highly constrained genes (sequences critical to organism function: strongly selected for; mutates very slowly.
