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Classification Biology I. Lesson Objectives Compare Aristotle’s and Linnaeus’s methods of classifying organisms. Explain how to write a scientific name.

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Presentation on theme: "Classification Biology I. Lesson Objectives Compare Aristotle’s and Linnaeus’s methods of classifying organisms. Explain how to write a scientific name."— Presentation transcript:

1 Classification Biology I

2 Lesson Objectives Compare Aristotle’s and Linnaeus’s methods of classifying organisms. Explain how to write a scientific name using binomial nomenclature. Summarize the categories used in biological classification. Compare and contrast species concepts. Describe methods used to reveal phylogeny. Explain how a cladogram is constructed.

3 Main Idea Biologists use a system of classification to organize information about the diversity of living things. Classification systems have changed over time as information has increased.

4 Early Systems of Classification Classification is the grouping of objects or information based on similarities Taxonomy is the branch of biology that groups and names organisms based on studies of their different characteristics. Aristotle grouped everything under plants or animals and then furthered organized by what type or where they lived.

5 Early Systems of Classification Aristotle’s system did not account for evolutionary relationships. Carolus Linnaeus developed a system that was based on physical and structural similarities. This way is the basis of modern classification systems. Modern classification systems are a two-word naming system called binomial nomenclature.

6 Early Systems of Classification The first word describes the genus and is capitalized. A genus consists of a group of similar species. The second word, which often describes a characteristic of the organism, immediately follows the genus name and is not capitalized. This is the species name.

7 Early Systems of Classification Latin is the language of scientific names. Scientific names are italicized or underlined. Now there is a system of trinomial nomenclature to further specify where a particular species might be located. COMMON NAMES DO NOT INDICATE RELATIONSHIPS AMONG ORGANISMS. A common name in one place is not the same as it is in another.

8 Biological Classification Natural relationships, external and internal structures, geographical distribution, and chemical make-up are considered in organizing. Classification provides a framework in which to study the relationships among living and extinct species. Dichotomous keys are helpful in identification because it has two descriptions at each step. The steps are followed until the key reveals the name of the organism.

9 Taxonomic Categories Groups are subdivided on the basis of more specific criteria. Any group of organisms is called a taxon. Organisms are ranked in arbitrary taxa that range from having very broad characteristics to very specific ones. The broader the taxon, the more general its characteristics, the more species it contains.

10 Taxonomic Categories Kingdom, Phylum, Class, Order, Family, Genus, Species King Phillip came over for grape soda is a mnemonic for learning the classification order. Genus and species are described previously. Family consists of a group of similar genera. EX. Cats, bobcats, lynxes, lion belong to family Felidae.

11 Taxonomic Categories An order is a taxon of similar families. A class is a taxon of similar orders. A phylum is a taxon of similar classes. Plants uses the taxon division instead of phylum. A kingdom is a taxon of similar phyla or divisions. There are 6 kingdoms.


13 Typological Species Concept Aristotle and Linnaeus thought of each species as a distinctly different group of organisms based on physical similarities. This is the idea of typological species. Concept is based on the idea that species are unchanging, distinct, and natural types.

14 Typological Species Concept The type specimen was an individual of the species that best displayed the characteristics of that species. When another specimen was found that varied significantly from the type specimen, it was classified as a different species. Concept has now been replaced.

15 Biological Species Concept Dobzhansky and Mayr defined a species as a group of organisms that is able to interbreed and produce fertile offspring in a natural setting. Called the biological species concept Some limitations – certain species can interbreed and produce fertile offspring but be of different species. –Ex. Wolves and dogs Doesn’t account for extinct species or species that reproduce asexually

16 Phylogenetic Species Concept A companion to the biological species concept The evolutionary species concept defines species in terms of populations and ancestry. Two or more groups that evolve independently from an ancestral population are classified as different species.

17 Phylogenetic Species Concept Recently has developed into the phylogenetic species concept Phylogeny is the evolutionary history of a species. Defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent.

18 How Evolutionary Relationships are Determined Structural similarities – homologous structures (same in arrangement, function, or both) denote common ancestors Breeding behavior – differences in mating behavior Geographical distribution – location of species on Earth Chromosomes – number and structure Biochemistry – DNA and protein sequences

19 Characters Characters are inherited features that vary among species. –Can be morphological or biochemical Shared morphological characters suggest that species are closely related and that they evolved from a recent common ancestor. Analogous characters do not indicate a close evolutionary relationship.

20 Characters Homologous characters might perform a different function but show similar structure that was inherited from a common ancestor. The number and structure of chromosomes provide information about evolutionary relationships among species. Similarities suggest a common evolutionary history.

21 Characters Scientists study and understand evolutionary relationships by sequencing DNA of different organisms. Organisms that are closely related have many similar sequences of nucleotides. The more sequences organisms share, the more likely they are to share a common ancestor.

22 Characters A molecular clock is a model that uses comparisons of DNA sequences to estimate how long species have been evolving. Mutations occur randomly in DNA and will build up in the chromosomes as time passes. The rate at which mutations occur does not stay the same.

23 Characters Because of inconsistency, scientists are trying to find genes that mutate at a relatively consistent rate throughout a range of organisms. The molecular clock is often used along with the fossil record to identify the time of divergence.

24 Phylogenetic Reconstruction Cladistics is a way to study evolutionary relationships that rebuilds phylogenies and hypothesizes evolutionary relationships based on shared characters. There are two main character types that need to considered when using cladistics: ancestral characters and derived characters.

25 Phylogenetic Reconstruction An ancestral character is found in a variety of groups within the line of descent. A derived character is present in one group within the line of descent, but it is not found in the common ancestor. A cladogram is a branching diagram that shows the proposed phylogeny of a species. –Similar to a pedigree

26 Phylogenetic Reconstruction The groups of a cladogram, called clades, have one or more related species. In a cladogram, two groups on diverging branches probably share a more recent ancestor than those groups farther away. The common ancestor at the nodes (place where branching occurs) is rarely a known organism, species, or fossil.

27 Phylogenetic Reconstruction

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