18.2 Modern Systematics I. Traditional ______________ A. Scientists use similarities in ___________ & ____________ to group organisms. 1. this approach is ____________. 2. Some groups look ____________ but turn out to be _____________ related. 3. Other groups look __________ but turn out to be _______________ related.

II. Phylogenetics A. Def – The study of the ___________ relationships between __________. B. It’s like trying to draw a huge family ____ over millions of _______________. C. Not all similar ____________ are inherited from a common _____________. 1. Ex.-_______ of an insect & the _______ of a bird. D. _____________ evolution = similarities in groups that are _____ closely related.

2. ___________ characters = Similarities that 2. ___________ characters = Similarities that arise through ______________evolution. E. This family tree, or __________ tree, represents a hypothesis of the relationships between ___________ groups. III. _______________ A. Objective method that unites ______________ with _______________. 1. Focuses on finding _____________ that are shared between ___________ groups because of shared ________________.

2. Ancestral character is defined as 2. Ancestral character is defined as having evolved in a common ________ of __________ groups. 3. ______ character = one that evolved in ____ group but ______ the other. C. Constructing a Cladogram 1. A __________ is a phylogenetic tree that is drawn in a ____________ way. 2. A ______ is a set of groups that are related by descent from a single ancestral ____________. 3. Outgroup = group that lacks some of the shared ___________________.

IV. Inferring Evolutionary Relatedness 1. refers to the ____________ structure or ____________ of organisms. 2. Organisms that share ancestral genes often show similarities during _______________. B. Molecular Evidence 1. Scientists now use __________ info. to infer phylogenies. 2. DNA _______ in a _______ is determined for several species 3. Then, each letter at each position is ____________.

C. Evidence of Order and Time 1. Cladistics can determine only the relative _______ of divergence, or ____________, in a phylogenetic tree. 2. The ________ record can often be used to infer the actual _______ when a group may have begun to “branch off.” D. Inference Using _____________ 1. This principle holds that the __________ explanation for something is the most ___________, unless strong evidence exists __________ that explanation. 2. Given two possible cladograms, the one that implies the _________ character changes between _________ is preferred