Chapter 18.2 Notes
Phylogenetics
■Scientists who study systematics are interested in ______, or the ancestral ______
______.
■Grouping organisms by similarity is often assumed to reflect phylogeny, but inferring phylogeny is complex in practice.
■Reconstructing a species’ phylogeny is like ______over millions of generations.
■Not all similar characteristics are inherited from a ______.
■Consider the wings of an insect and the wings of a bird.Both enable flight, but the structures of the two wings differ
■Fossil evidence also shows that insects with wings existed long before birds appeared.
■Through the process of ______, similarities may evolve in groups that are not closely related.
■Similar features may evolve because the groups have adopted similar habitats or lifestyles.
■Similarities that arise through convergent evolution are called ______.
■Grouping organisms by similarities is ______.
■Some scientists may think one character is important, while another scientist does not.
■For example, systematistshistorically ______, giving importance to characters like feathers. But they are more closely related than initial thought.
Cladistics
■______ is a method of analysis that infers phylogenies by careful comparisons of shared characteristics.
■Cladistics focuses on finding ______ that are shared between different groups because of
______.
■A shared character is defined as ______ if it is thought to have evolved in a common ancestor of ______.
■A ______character is one that evolved in ______.
■For example, the production of seeds is a character that is present in all living conifers (pine trees) and flowering plants, and some prehistoric plants.
■Seed production is a______among those groups.
■The production of ______is a derived character that is only shared by flowering plants.
■A ______is a phylogenetic tree that is drawn in a specific way.
■Organisms are grouped together through ______.
■All groups that arise from ______on a cladogram belong to a clade.
■A ______is a set of groups that are related by descent from a single ancestral lineage.
■Each clade is usually compared with ______, or group that doesn’t have some of the shared characteristics.
■The images shows a cladogram of different types of plants.
■Conifers and flowering plants form a clade.
■Mosses form the outgroup, they have no similarities with the other groups.
Inferring Evolutionary Relatedness
Morphological Evidence
■______refers to the physical structure or anatomy of organisms
■An important part of morphology in multicellular species is the ______from embryo to adult.
■Organisms that ______often show similarities during the process of development.
■For example, the jaw of an adult develops from the same part of an embryo in every vertebrate species.
Molecular Evidence
■Scientists can now use ______to infer phylogenies.
■Recall that as genes are passed on from generation to generation, ______.
■Some mutations may be passed on to all species that have a ______.
Evidence of Order and Time
■Cladistics can determine only the relative order of ______, or branching, in a phylogenetic tree.
■The fossil record can often be used to infer the actual time when a group may have begun to “______.”
■For example, using cladistics, scientists have identified lancelets as the closest relative of vertebrates.
Inference Using Parsimony
■Modern systematistsuse the ______ to construct phylogenetic trees.
■This principle holds that the ______for something is the most reasonable, unless strong evidence exists against that explanation.
■Given two possible cladograms, the one that implies the fewest character changes between points is preferred.