Building trees

The Great Clade Race Long, long ago, in a place far, far away, eight runners (A–H) met in the woods for a foot race. All the runners began the race at a single starting point, but, at various points, the course forked. Each series of forks led to a separate finish line at the other end of the woods. At each fork, runners chose which path to take. To keep track of the race, each runner carried a card that was stamped at check-in stations distributed at various points along the paths. Each runner had his or her card stamped at each check-in station they passed. Use these cards to try and reconstruct the course of each runner and the placement of check-in stations.

The Great Clade Race 1. All runners completed the race, i.e., nobody stopped midday along a path. 2. When the paths split, they forked into two new paths, not three or more. 3. Once paths diverged, they never reunited. 4. Check-in stations were located between forks in the paths.

Bony Ray Amniotic SkeletonfinsEggLactation Perch1100 Guppy1100 Shark0000 Cat1011 Dog1011 Lizard1010

Terms for cladistic tree building Character Character state Ancestral character state (Plesiomorphic) – Symplesiomorphy Derived character state (Apomorphic) – Synapomorphy – Autapomorphy

Synapomorphies are marked Examples of symplesiomorphies?

How can we determine synapomorphy vs. symplesiomorphy?

Outgroups Outgroups are the most common method for rooting trees Outgroup criteria 1. “Outside” the group of study 2.Closely related enough to be informative