Bianca Hernandez

Biology Honors P6

11 April 2014

CH.18 CLASSIFICATION

Scientists have been trying to identify, name, and find order in our diverse earth for a long time, which has led us to classification.

THINK ABOUT IT

Key QuestionsWhat are the goals of binomial nomenclature and systematics? How did Linnaeus group species into larger taxa?

18.1 FINDING ORDER IN DIVERSITY

ASSIGNING SCIENTIFIC NAMES• 1) understanding + studying diversity • describe and name each species, which is useful b/c if we refer to each species by one name only, everyone will use the name

•what type of name?• Sometimes be misinterpreted b/c variations in languages and places , which leads to different species sharing common names• 18th century began the use of Latin/Greek names per species

•Dichotomous Key• Used to identify organisms• 1) using series of paired statements, which will describe alternative possible characteristics of an organism• 2) paired statements which usually describe presence or absence of certain visible characteristics/structures• 3) entire processes leads into subsets until you achieve the desired outcome

Ex. Of Dichotomous Key

BINOMIAL NOMENCLATURE• Carolus Linnaeus developed the binomial

nomenclature – a two-word naming systemEach species is assigned a two-part scientific name1) scientific names are written in italic 2) 1 word = C ; 2 word = c3) the first part is the genus and the second is the

species • Genus – a group of similar species• Species – description of an important trait / an

organism’s habitat

BINOMIAL NOMENCLATURE

RED MAPLE SCIENTIFIC NAME = Acer rubrum GENUS Acer = CONSIST OF ALL MAPLE TREESSPECIES rubrum = RED MAPLE COLOR

CLASSIFYING SPECIES INTO LARGER GROUPS

try to organize/classify living and fossil species into larger groups that will have a biological meaning • Systematics – science of naming and grouping

organisms • These groups are referred to as – taxa • Ex. Professor • Science Professor

THE LINNAEAN CLASSIFICATION SYSTEM

• Linnaeus developed a classification system that organized species into taxa that formed a hierarchy/set of ordered ranks

Seven hierarchical taxa: Species, Genus, Family, Order, Class, Phylum, and Kingdom

• He grouped species according to anatomical similarities and differences

• Family – where several genera that share many similarities are grouped into a larger category

• Order – closely related families are grouped into the next larger rank

• Class – similar orders are grouped• Phylum – classes are grouped; includes organisms that

are different but share important characteristics • Kingdom – largest and most inclusive rank• (K)ing (P)hilip (C)ame (O)ver (F)or (G)ravy (S)oup

PROBLEMS WITH TRADITIONAL CLASSIFICATION

• In a sense, members of a species determine which organisms belong to that species by deciding with whom they mate and produce fertile offspring, which mean there is a “natural” definition of species• Researchers define Linnaean ranks above the level of species b/c over time systematics have emphasized a variety of characteristics and some of these groups have been defined in different ways at different levels• Ex. Linnaean’s classification of organisms according to visible similarities and differences • Modern systematics apply Darwin’s ideas to classification and also try to look beyond simple similarities and differences so thy can ask questions about evolutionary relationships

Key QuestionsWhat is the goal of evolutionary classification?What is a cladogram?How are DNA sequences used in classification?

18.2 MODERN EVOLUTIONARY CLASSIFICATION

EVOLUTIONARY CLASSIFICATION

•The concept of descent with modification led to the study of phylogeny – the evolutionary history of lineages•Advances in phylogeny led to phylogenetic systematics

Goal is to group species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences

COMMON ANCESTORS

•Phylogenetic systematics places organisms into higher taxa whose members are more closely related to one another•The larger the taxon is, the further back in time all of its members shared a common ancestor

CLADES• Classifying organisms according to these rules places them into groups called clades – group of species that includes a single common ancestor and all descendants of that ancestor which include living and extinct•How are clades different from Linnaean taxa?• Clade must be a monophyletic group – includes a single common ancestor and its descendants• Some groups of organisms before the arrival are monophyletic• Some are paraphyletic – the group includes a common ancestor but excludes one or more groups of descendants, which means those excluded groups are invalid under evolutionary classification

Ex. Of Mono/Paraphyletic taxon

CLADOGRAMS • Modern evolutionary classification use a method

called cladistics analysis, which compares carefully selected traits to determine the order in which groups of organisms branched off from their common ancestors

Cladogram – links groups of organisms by showing how evolutionary lines, or lineages, branched off from common ancestors

• How do you build a cladogram?• 1) the diagram shows a single ancestral lineages

splitting into two • The point splitting is the node – represents the last

point which the two new linages shared a common ancestor

• 2) the bottom, or root – the common ancestor shared by all the organisms

• 3) a cladogram’s branching patterns indicate the degree of relatedness among organisms

Different Types of Cladograms

Ex. of Cladogram

Ex. of Cladogram

DERIVED CHARACTERISTICS • In contrast to Linnaean taxonomy, cladistic analysis focuses on certain kinds of characters, or derived characteristics when assigning organisms into clades •Derived characteristics – a trait that arose in the most recent common ancestor of a particular lineage and was passed along to its descendants

LOSING TRAITS

• Ex. Clade Tetrapoda have a derived character of four limbs• Snakes are part of this clade but are not four limbed•How does this work?• The ancestors of the snakes did have four limbs, but somewhere in the lineage that lead to our modern snake, the trait was lost• Because distantly related groups of organisms can sometimes lose the same character, systematics are very cautious about using the absence of a trait as a character in their analysis• You may ask what about whales since they are also not four limbed, but we can clearly tell snakes are more closely related to other reptiles than whales!

INTERPRETING CLADOGRAMS • 1) the lowest node represents the last common ancestor • 2) the forks in the cladogram show the order in which various groups branched off• 3) the positions of various characteristics in the cladogram reflect the order in which those characteristics arose in the lineage • 4) each derived character listed along the main truck of the cladogram defines a clade• 5) derived characters that occur “lower” on the cladogram than the branch point for the clade are not derived for that particular clade

Ex. of Cladogram

DNA IN CLASSIFICATION: GENES AS DERIVED CHARACTERS

•Since all genes mutate over time, shared genes contain differences that can be treated as derived characters• Similarities and differences in DNA con be used to develop hypotheses about evolutionary relationships

In general, the more derived genetic characters two species share, the more recently they shared a common ancestor and the more closely they are related in evolutionary terms

NEW TECHNIQUES SUGGEST NEW TREES

• The use of DNA characters in cladistic analysis has helped to make evolutionary trees more accurate• Ex. The hooded vulture from Africa, the American vulture, and Storks • Both the hooded and American vultures are in the falcon clade• But American vultures do something odd when they overheat• They urinate on their legs, as they rely on the evaporation to cool them down• Storks also do this, which has led Biologists to try and piece this puzzle together

•Molecular analysis shows that the DNA from the American vulture is more similar to storks than African vultures• Suggests that American vultures and storks share a more recent common ancestor than American and African vultures

•Molecular analysis is a powerful tool that is now routinely used by taxonomists to supplement data from anatomy

Key QuestionsWhat are the six kingdoms of life as they are now identified?What does the tree of life show?

18.3 BUILDING THE TREE OF LIFE

CHANGING IDEAS ABOUT KINGDOMS

• Biologists learned that the two kingdoms – Animalia and Plantae – did not reflect the full diversity of life• Five Kingdoms• Researchers began to study microorganisms which led to the discovery that single-celled organisms were significantly different from plants and animals• They then placed all microorganisms into the kingdom Protista•Next, they placed yeast and molds + mushrooms into the kingdom Fungi• Scientists realized that bacteria lack nuclei, mitochondria, and chloroplasts that were found in other forms of life = prokaryotes (bacteria) placed in Monera

CHANGING IDEAS ABOUT KINGDOMS• Six Kingdoms• In the 1990’s, researchers realized that the organisms in Kingdom Monera were actually two genetically and biochemically different groups• This led to separating Monera into Eubacteria and Archaebacteria

Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia

• Three Domains• Domain – a larger, more inclusive category than a kingdom• 3 Domains are: Domain Bacteria, which corresponds to kingdom

Eubacteria, Domain Archaea, which corresponds with kingdom Archaebacteria, and Domain Eukarya, which corresponds with kingdoms Fungi, Plantae, Animalia, and “Protista”

• There are quotations around Protista b/c it’s a paraphyletic group and there is no way to put all unicellular eukaryotes into a clade that contains a single common ancestor, all of its descendants, and only those descendants

THE TREE OF LIFE• Modern evolutionary classification is a rapidly changing

science with the difficult goal of presenting all life on a single evolutionary tree

• Biologists regularly change not only the way organisms are grouped, but also sometimes the names of groups

• Different from cladograms b/c they are visual presentations of hypotheses about relationships, and not hard fact

Shows current hypotheses regarding evolutionary relationships among the taxa within the three domains of life

• Domain Bacteria• Bacteria – unicellular and prokaryotic• Cells have thick, rigid walls that surround a cell membrane• Cell walls contain a substance known as peptidoglycan • They are ecologically diverse, ranging from free-living soil

organisms to deadly parasites• Some photosynthesize, while others don’t and some need

oxygen to survive while, others are killed by oxygen

THE TREE OF LIFE• Domain Archaea • Archaea – unicellular prokaryotes• Their cell walls do not contain peptidoglycan• Live in extreme environments such as: volcanic hot

springs, brine pools, and black organic mud that is totally lacking oxygen

• Some of them can only survive in the absence of oxygen• Cell membranes contain unusual lipids not found in any

other organisms • Domain Eukarya• Eukarya – all organisms that have a nucleus• “Protists” – Unicellular Eukaryotes • Some people still use the name “protists” for these

organisms, but scientists have known for years that they do not have a valid clade

THE TREE OF LIFE• Domain Eukarya• Fungi • Heterotrophs with cell walls containing chitin • Most feed on dead or decaying organic matter• Fungi secrete digestive enzymes into their food source to

absorb the small molecules into their bodies

• Plantae • Autotrophs with cell walls that contain cellulose• Can carry out photosynthesis • Cannot move from place to place

• Animalia• Multicellular and heterotrophic • Animal cells do not have cell walls• Most can move

CREDITS• Miller & Levine Biology ( ©2010) • http://www.youtube.com/watch?v=F38BmgPcZ_I • http://evolution.berkeley.edu/evosite/evo101/IIDClassification.shtml• http://www.ucmp.berkeley.edu/clad/clad5.html• http://www.ucmp.berkeley.edu/glossary/gloss1/phyly.html• http://www.ucmp.berkeley.edu/clad/clad5.html