BIOLOGY 3 Lecture Notes - Lecture 27: Nuclear Dna, Willi Hennig, Ribosomal Rna
Document Summary
All cells have ribosomes for protein synthesis; comparing rrna sequences provides a reliable indicator of similarity. Dna dna hybridization separates the dna strands of two species and combines the strands; the more closely related the two species, the more the dna strands stick together. Dna hybridization shows chimpanzees closer to humans than to other apes. Mitochondria dna (mtdna) changes ten times faster than nuclear dna. Mtdna is often used for closely related species; north american songbirds were found to have diverged well before retreating glaciation 250,000 100,000 years ago. Nucleic acid changes are not tied to adaptation; the fairly constant changes provide a molecular clock. Comparison of mtdna sequences equated a 5. 1% nucleic acid difference among songbird species to 2. 5 million years the fossil record can then be used to calibrate the clock and confirm the hypothesis drawn from molecular data. Cladistic systematics is based on work of willi hennig.
