UT Arlington BIOL BIOL 3427 - ch18 (6 pages)

Previewing pages 1, 2 of 6 page document View the full content.
View Full Document

ch18



Previewing pages 1, 2 of actual document.

View the full content.
View Full Document
View Full Document

ch18

128 views


Pages:
6
School:
University of Texas at Arlington
Course:
Biol Biol 3427 - Plant Science
Unformatted text preview:

Chapter 18 CLASSIFICATION AND SYSTEMATICS We have grouped organisms for easier study by comparing similarities and differences SYSTEMATICS the study of the diversity of organisms and their comparative and evolutionary relationships It includes comparative anatomy comparative biochemistry comparative physiology etc CLASSIFICATION OR TAXONOMY is the ordering of organisms into groups It includes the principles procedures used in classification PHYLOGENY refers to the evolutionary history of a species or group of species in terms of their derivations through evolutionary processes which species share a common ancestor which species share a more distant ancestor etc Systematics is the study of biological diversity and evolutionary history of organisms Systematics includes Taxonomy the science of identifying and classifying organisms Phylogenetics the study of the evolutionary history of organisms Nomenclature the system used in naming organisms Natural selection has shown that all organisms are related to each other genetically All are part of a large phylogeny Scientifically valid system of naming plants nomenclature should reflect phylogeny that is evolutionary relationship At the end of the XIX Century scientists began to develop a natural system of classification in which closely related organisms are classified together and began to assign plant names on the basis of phylogenetic relationship LEVELS OF TAXONOMIC CATEGORIES The present system of nomenclature was devised by Carolus Linnaeus Carl von Linne a Swedish botanist who lived in the 18th Century Linnaeus published in 1753 a book called Species Plantarum the kinds of plants Binomial system of nomenclature Genus species epithet scientific name of the plant Hierarchical classification groups within groups A taxonomic grouping is called a taxon Taxonomy is hierarchical taxa are grouped into broader taxa Species are grouped into genera sing Genus Genera into families families into orders orders into classes classes into divisions divisions into kingdoms There are intermediate taxonomic categories e g superfamily or subspecies Except for the kingdom genus and species level the taxon must have a certain ending to indicate the classification level phyta for Division e g Chlorophyta opsida for Class e g Liliopsida ales for Order e g Fabales aceae for Family e g Fabaceae Each family name is named after one of its genera e g Rosaceae after the genus Rosa Some old names used before the adoption of the new rules of nomenclature have been conserved by convention These are named nomina conservanda conserved names For example the daisies and asters family have two names a conserved old name Compositae and a new name according to the modern rules of nomenclature Asteraceae Both are equally valid CLADISTICS A species evolves into two species as populations accumulate distinct alleles The two new species usually strongly resemble one another Reproductive isolation prevents the sharing of new alleles caused by mutations Plants may resemble one another because 1 They evolved from a common ancestor 2 They have undergone convergent evolution A feature or a trait is called a character A character may be a morphological characteristic e g presence of hairs shape of shell etc A character may also be a trait at the cellular biochemical or molecular level e g a particular nucleotide sequence A character may have several character states e g white or purple flowers hairs long or short A base or C base in particular nucleotide sequence Ancestral or plesiomorphic characters are found in the common ancestor of daughter species o Symplesiomorphic characters are ancestral characters shared by modern clades Derived or apomorphic characters have evolved from the ancestral character o Synapomorphic characters are derived characters found in two or more species and suggest a close common ancestor Shared derived characters are evidence of evolutionary relationship The resemblance of plants that result when two distinct evolutionary lines respond to similar environments and selection pressures is called convergent evolution Taxa may be similar because they share ancestral character states or derived character states but only the derived character states that are shared among taxa indicate monophyletic groups and enable us to infer phylogeny successfully See the example on page 416 cacti and succulent euphorbs Character states that are restricted to a single lineage are sometimes called autapomorphies Homology same feature in different species is derived from a common ancestor e g the forelimb of vertebrates Homoplasy a feature that has evolved two or more time independently of the other and thus does not have a common origin Homoplasies are also called analogous features or characters Study the vocabulary on Table 18 3 page 421 Study Cacti as Examples of Evolutionary Diversification pages 422 425 Dissimilarities between plants can be difficult to assess Mutations that affect production distribution and sensitivity to hormones result in large changes of the phenotype between two closely related species Mutations that affect early stages of development such as the embryo or bud meristems can cause closely related species to look deceptively dissimilar Certain features are considered more significant in evaluating evolutionary relationship Features that are the result of complex metabolic interactions and the influence of many genes tend to evolve more slowly than those with simple metabolic controls by one or two genes DNA sequencing is a new tool for analyzing evolutionary relationships DNA sequencing has its own limitations and ambiguities e g how many nucleotide differences are needed to conclude that two genomes represent two distinct species UNDERSTANDING CLADOGRAMS A cladogram is a diagram that shows evolutionary patterns by means of a series of branches Each point at which a cladogram branches is called a node and represents the divergence of one taxon into two taxa All branches that extend from any particular point represent the descendants of the original group their common ancestor The ancestor and all the branches derived from it represent a clade A node represents a detectable change that created the two new groups See Fig 18 4 Shared derived characters are evidence of evolutionary relationship Phylogenetic classification should be monophyletic Monophyletic means that all the members of a taxon regardless of rank are descendants of a common ancestor


View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view ch18 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view ch18 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?