Objectives – I CAN

1. Explain why biologists need and have

a taxonomic system

2.Describe the components of a species’

scientific name.

3. Describe the structure of the modern

Linnaean system of classification.

18.1 The Need for Systems

About 1.7 million species have been

named and described by scientists.

Scientists think that millions more are

undiscovered thus there is a need to

organize species.

The practice of naming and classifying

organisms is called taxonomy.

The Need Continued

Taxonomic systems allow consistency in

the way organisms are grouped and

how the knowledge of them is organized

Scientists group organisms into large

categories and then into smaller more

specific categories.

The general term for any one of these

categories is a taxon (plural, taxa)

Scientific Nomenclature

Various naming systems were invented in the early days of European biology Some used long, descriptive Latin phrases called

polynomials.

A simpler and more consistent system was developed by Swedish biologist Carl Linnaeus in the 1750s Linnaeus introduced a two-word naming system called

binomial nomenclature.

System universally adopted and the two-word name is referred to as a scientific name

Naming Rules No 2 species can have the same scientific

name. Names are always italicized or underlined

All scientific names are made up of two Latin or Latin-like terms first term: genus names

○ written first and is capitalized

○ All the members of a genus share the same genus name

second term: species identifier, is lowercase and often descriptive of the organism.

Nomenclature Example

For example, the scientific name Apis

mellifera belongs to the European

honeybee.

Mellifera derives from Latin word for honey

Linnaean System Organisms are grouped at successive levels of

the hierarchy based on similarities in their form and structure until the individual species is identified

The 8 levels of modern classification are domain, kingdom, phylum, class, order, family, genus, species. The domain category was invented after Linnaeus’ time

and recognizes the most basic differences among cell types

There are 6 kingdoms that fit within the three domains

Linnaean System Continued

A phylum is a subgroup within a kingdom

A class is a subgroup within a phylum

Order is a subgroup within a class

Family is a subgroup within an order

Genus a subgroup within a family

Each genus is made up of species with uniquely shared traits, such that the species are thought to be closely related

18.2 Objectives

Describe what systematics and

phylogenetics are and their

relationship to each other.

The Terms

Systematics: the branch of biology that deals with classification and nomenclature aka taxonomy plus phylogenetic characters (evolutionary tracts).

Phylogenetics - is the branch of biology concerned with the analysis of molecular sequencing data to study evolutionary relationships among groups of organisms. Phylogenetics is used to determine evolutionary

relatedness/closeness which helps correctly classify organisms (systematics)

Cladistics a phylogenetic classification system that uses shared derived characters and ancestry as the sole criterion for grouping taxa. Cladistics is an objective method that unites

systematics with phylogenetics.

Traditional Systematics Scientists have traditionally used similarities in

appearance and structure to group organisms, however, this approach has been problematic. (taxonomy without phylogenetics)

Example: Birds were seen as a separate, modern group that was not related to any reptile group.

Fossil evidence has convinced scientists that birds evolved from one of the many lineages of dinosaurs.

Some groups look similar but turn out to be distantly related and vice versa often due to convergent evolution.

Convergent evolution is when organisms develop a similar trait because they live in a similar environment not because they are related evolutionarily

Phylogenetics

Scientists who study systematics are interested in phylogeny, or the ancestral relationships between species. Grouping organisms by similarity is often

assumed to reflect phylogeny, but inferring phylogeny is complex in practice.

Reconstructing a species’ phylogeny is like trying to draw a huge family tree over millions of generations.

How is phylogeny determined?

First similar characteristics are observed but not all characters are inherited from a common ancestor.

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.

Phylogenetics

Remember sometimes convergent

evolution allows similarities to evolve

in groups that are not closely related.

These evolve because the groups have

adopted similar habitats or lifestyles.

Similarities that arise through

convergent evolution are called

analogous characters.

Phylogenetics

Fossil evidence now shows that birds are considered part of the “family tree” of dinosaurs.

This family tree, or phylogenetic tree, represents a hypothesis of the relationships between several groups

Different types of evidence used to

help infer phylogeny

1.Morphological Evidence

Morphology refers to the physical structure or anatomy of organisms.

Scientists must look carefully at similar traits, to avoid using analogous characters for classification. An important part of morphology in

multicellular species is the pattern of development from embryo to adult.

Evidence Continued

2. Molecular Evidence

Scientists can now use genetic information to infer phylogenies.

Recall that as genes are passed on from generation to generation, mutations occur.

Some mutations may be passed on to all species that have a common ancestor.

Evidence Continued

3. Evidence of Order and Time

Cladistics can determine only the

relative order of divergence, 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 “branch off.”

18.2 Objectives

Explain how cladistics is used to form evolutionary relationships.

Construct a Cladogram using phylogeny

REMEMBER

Cladistics a phylogenetic classification system that uses shared derived characters and ancestry as the sole criterion for grouping taxa. Cladistics is an objective method that unites

systematics with phylogenetics.

Cladistics

Cladistics uses shared derived characters and ancestry as the sole criterion for grouping taxa. Cladistics is an objective method that unites

systematics with phylogenetics.

Cladistic analysis is used to select the most likely phylogeny (remember it’s a hypothesis) among a given set of organisms (and can change with new evidence).

Cladistics continued

Cladistics focuses on finding characters that are shared between different groups because of shared ancestry.

A shared character is defined as ancestral if it is thought to have evolved in a common ancestor of both groups. Seed production is a shared ancestral character

among those groups all living conifers and flowering plants, and some prehistoric plants.

A derived character is one that evolved in one group but not the other.

Cladistics continued

Cladistics infers relatedness by

identifying shared derived and

ancestral characters among groups,

while avoiding analogous characters.

REMEMBER: Similarities that arise

through convergent evolution are

called analogous characters

Cladogram

Scientists construct a cladogram to show relationships between groups.

A cladogram is a phylogenetic tree that is drawn in a specific way.

All groups that arise from one point on a cladogram belong to a clade.

A clade is a set of groups that are related by descent from a single ancestral lineage

Cladogram continued

Each clade is usually

compared with an

outgroup, or group

that lacks some of the

shared characteristics.

Leaf type Petal Color Dot color Thorns present Number of petals

A

B

C

B C

A

B

Data matrix

Dichotomous Keys

What is it?

Identification key that contains major characteristics of groups of organisms

What is it used for? To identify an unknown organism

How does it work?

Key contains list of contrasting descriptions, you identify which character your unknown organism has and eventually you ID your unknown.