Friday, March 1
Bell Work:
Complete OGT questions 2­6.
1
17.2 Classification Based on Evolutionary Relationships
Scientists agree that species should be classified based on evolutionary relationships.
­This is done by using evidence from living species, the fossil record, and molecular data.
Phylogeny­ evolutionary history for a group of species
­Shown as a branching tree­like diagram (similar to a family tree)
­Branches show how different groups of species are related to one another.
2
• Cladistics­ system of classification that is based on phylogeny (used to make evolutionary trees)
­Based on common ancestry
­Goal: Place species in the order in which they descended from a common ancestor
• Cladogram­ an evolutionary tree that proposes how species may be related to one another.
• ­Clade­ a group of species that shares a common • ancestor
• *Through the course of evolution, certain traits change in some species in a clade and stay the same in others.
• *These traits are used to determine evolutionary relationships
3
Derived Characters­ traits that differs in structure or function from that found in the ancestral line for a group of species.
­Cladograms are used to figure out which derived characteristics are shared by which species.
­They are shown as the hash marks between branches
*Node­ The place where a branch splits
*Clade­ use the 'snip it' rule and cut just under a node
4
5
Increases technology allows certain DNA sequences to be used as derived characters when it is shared amongst species.
­In many cases DNA evidence agrees with physical similarities.
­Other cases it turns scientists in completely different directions
­DNA is considered to have "the last word" in determining how species are related.
6
Monday, March 5
Bell Work:
What does a cladogram show? What is a node on a cladogram?
7
8
9
10
11
12