University:
Felician University
Course:
BIO-209 | Evolution
Academic year:

2020
Views:

391

Pages:

1
Author:

larbiwxcvbn

CLADISTICS Clades Cladistics involve classifying organisms into groups of species (clades) • A clade consists of a single common ancestor and all descendants CLADE NOT A CLADE Cladograms are tree diagrams where each branch point represent the splitting of two new species groups from a common ancestral species • Each branch point (node) represents a speciation event • The more nodes between groups, the less related the groups are Structural Evidence Molecular Evidence Historically, cladograms have been constructed based on structural characteristics, however this not always a reliable method for establishing evolutionary connections • Related species may have distinctive (homologous) features • Unrelated species may have similar (analogous) features Cladograms are now being generated via a comparison of biochemical evidence (i.e. DNA or amino acid sequences) • Related species will have sequences with more similarities • Amino acid sequences will accumulate differences at a slower rate to DNA sequences (due to degeneracy) HOMOLOGOUS ANALOGOUS Structures look different Structures look similar Due to different selection pressures Due to common selection pressures Species do share a common ancestry Species do not share a common ancestry Evidence of divergent evolution Evidence of convergent evolution E.g. Pentadactyl limb E.g. Fins (whale vs shark) If a sequence accumulates mutations at a constant rate, the time of divergence can be calculated based on the number of mutations between the two species (molecular clock) Human Monkey Haemoglobin β-chain: Dog Bird Similarities Fish Differences Cladograms Structural Data: Compare characteristics via a table Example: Humans and Other Primates Lungs Endothermic Hair / skin Fish – – – Lizard ✔ – – Bird ✔ ✔ – Rodent ✔ ✔ ✔ Molecular Data: Compare sequences via multiple alignment 4 lizard F S T A A F R P P H T V 3 bird F S T A A F R G G H T I 1 rodent F S T A A F R F G H T I 0 Consensus F S T A A F R F G H T I Mutations fish F A A A A F Q F G F T I Millions of years ago 0 5 10 15 20 25 Gibbon Orangutan Gorilla Chimp Man