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TRANSCRIPT
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.
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.