Unit 2 - Evolutionary Patterns -- Phylogeny and Fossils - Unit 2 Evolutionary Patterns Phylogeny and Fossils Section 23.1 Reading a Phylogenetic Tree

Unit 2 - Evolutionary Patterns -- Phylogeny and Fossils -...

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Unit 2- Evolutionary Patterns – Phylogeny and Fossils: Section 23.1 – Reading a Phylogenetic Tree: Reading a Phylogenetic Tree: o Speciation can be thought of as a process of branching o Imagine what happens as this process occurs over and over in a lineage through time As species proliferate (multiply), their evolutionary relationships to one another unfold in a treelike pattern With present-day species as the tips of branches Last common ancestors indicated by the point (called a node) from which present-day species branched off o Node: The point where a branch splits Represents the common ancestor from which the descendant species diverged Phylogenetic Trees Provide Hypotheses of Evolutionary Relationships: o Phylogenetics is one of two related disciplines in systematics – the study of evolutionary and genetic relationships among organisms The other is taxonomy – the classification of organisms o Taxonomy: The aim of taxonomy is to recognize and name groups of individuals as species, and, subsequently, to group closely related species into the more inclusive taxonomic group of the genus, and so on up through the taxonomic ranks – species, genus, order, class, phylum, kingdom, domain Taxonomy provides us with a hierarchical classification of species in more and more inclusive groups, giving us a convenient way to communicate information about the features each group possesses o Phylogenetics: Aims to discover the pattern of evolutionary relatedness among groups of species or other groups by comparing their anatomical or molecular features, and to depict these relationships as a phylogenetic tree Phylogenetic tree: o A hypothesis about the evolutionary history, or phylogeny, of the species o Phylogenetic trees are hypotheses because they represent the best model, or explanation, of the relatedness of organisms on the basis of all the existing data However, as with any model or hypothesis, new data may require adjustments to the pattern of the tree o Many phylogenetic trees explore the relatedness of particular groups of individuals, populations, or species
o At a much larger scale, universal similarities of molecular biology indicate that all living organisms are descended from a single common ancestor This means that we can attempt to build a phylogenetic tree for all species, commonly referred to as the tree of life o Figure 23.2 shows a phylogenetic tree for vertebrate animals The informal name at the end of each branch represents a group of organisms, many of them familiar We will sometimes find it useful to refer to groups of species this way, rather than name all the individual species or list the characteristics they have in common It is important, however, to remember that such named groups represent a number of member species o If, for example, we were able to zoom in on the branch labeled “frogs”, we would see that it consists of many smaller branches, each representing a distinct species of frog

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