Glencoe Biology - Mrs. Harrison's Science Site

Cladograms (17.2) State Standard SB3C. Examine the evolutionary basis of modern classification systems. Chapter 17

Organizing Lifes Diversity 17.2 Modern Classification Cladistics classifies organisms according to the order that they descended from a common ancestor & reconstructs phylogenies based on

shared characters. Scientists consider two main types of characters when doing cladistic analysis. An ancestral character is found within the entire line of descent of a group of organisms. Derived characters are present in members of one group of the line but not in the common ancestor.

Chapter 17 Organizing Lifes Diversity 17.2 Modern Classification Cladograms

Cladograms are created using derived characters. It is a branching diagram that represents proposed evolutionary history of species. The greater the number

of derived characters shared by groups, the more recently the groups share a common ancestor. Reading Cladograms If the trait (character) falls

below the organism, then the organism has that trait. If the trait is above the organisms, then the organisms lacks that trait. The organism with the least traits shared with the others is called the outgroup.

The organisms that share the most derived characters are considered the most closely related.