Lecture 6B

Lecture 6B - 1/29/09 Overview I. What is a phylogeny? II....

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1/29/09 1 Overview I. What is a phylogeny? II. History III. How do we read trees? IV. How do we build trees? A. characters B. reasons for similarities 1. homology 2. homoplasy 3. shared & derived homologies C. tree building techniques 1. outgroup comparisons 2. parsimony 3. maximum likelihood V. Is there such a thing as a fish? VI. Why are phylogenies useful? VII. Molecular clocks Usually don’t have any idea what is shared, derived How do you find out? D. Tree building techniques 1. Outgroup comparisons 2. Parsimony 3. Maximum likelihood Outgroup comparisons Ingroup – a group of taxa that are of interest, assumed to be monophyletic Outgroup – one or more taxa assumed to be phylogenetically outside the ingroup, although related Example – gorillas as outgroup to humans, chimps, bonobos Outgroup comparisons can distinguish between ancestral and derived character states Outgroup comparisons amniotes - animals that have an egg membrane, amnion, during development Outgroup comparisons Imagine amniotes: mouse, kangaroo, eagle, crocodile, tortoise, robin Mouse and kangaroo are viviparous, others oviparous Vivipary & ovipary - which is ancestral, which is derived? Use outgroup
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Outgroup – frogs/salamanders Outgroup breeds oviparously - ancestral state Assume state a is ancestral state, because of outgroup D. Tree building techniques 1. Outgroup comparisons 2. Parsimony – principle for developing phylogenies Old concept (1300s) assumes that the simplest explanation is most likely to be correct Parsimony analysis finds the tree with fewest evolutionary changes Why does this work? Successful evolutionary change is unlikely, assume it happens infrequently Example: Octopuses have an image forming “camera” eye, similar to many vertebrates Octopuses share many other traits with mollusks Is the camera eye due to homology or homoplasy? Freeman and Herron fig 4.6
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/29/2009 for the course BILD BILD 2 taught by Professor Schroeder during the Spring '08 term at UCSD.

Page1 / 7

Lecture 6B - 1/29/09 Overview I. What is a phylogeny? II....

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online