Basic Taxonomic Concepts &
Principles, Description,
Nomenclature, Identification, And
Classification
Module
BioTam
General Biology 2
Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
OBJECTIVES
This module entitled, “Basic Taxonomic Concepts and Principles,
Description, Nomenclature, Identification, and Classification”, will elaborate
your understanding and discuss about the evolutionary history of the
biological diversity and achieve the following learning competencies:
1. Explain how the structural and developmental characteristics and
relatedness of DNA sequences are used in classifying living things;
2. Identify the unique/distinctive characteristics of a specific taxon
relative to other taxa;
3. Describe species diversity and cladistics, including the types of
evidence and procedures that can be used to establish evolutionary
relationships; and
4. Differentiate the 3-Domain Scheme from the 5-Kingdom Scheme of
classification of living things.
INTRODUCTION
Did you know that animals and fungi are more closely related to each
other than either of them is to plants?
A phylogeny, the evolutionary history of a species or group of species,
reveals and explains that the data from the DNA samples of animals –
including humans – and fungi like mushrooms are most likely related despite
of their difference in appearance.
Figure 1.1 - Fungi, animals, and plants relationship
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
TAXONOMY
Taxonomy is the science of classifying organisms. It results in
classifications that allows storage, retrieval, and communication of
information about organisms. Taxonomy is the branch of biology that groups
and names organisms based on studies of their shared characteristics.
DISCOVER
Survey and inventory of existing collections
DIAGNOSE
Comparative morphology, and character
discontinuity
DESCRIBE
Formal scientific destinction, and specimen
and locality data
NAME
Scientific name, and publishing in scientific
journal
CLASSIFY
Hierarchical classification, and biodiversity
information portal
Figure 1.2 – Taxonomic Methodology
The method of taxonomy includes: the discovery of species, the
recognition and diagnosing of taxa based on characters (e.g., morphological,
molecular, behavioral, etc.), the formal description and naming of species,
and the placement of species within a hierarchical classification.
BINOMIAL NOMENCLATURE
Do you want to know how species are being identified?
In the early years of 1700s, Carolus Linnaeus have developed a
system that classifies organisms based on their characteristics that is still
used up to the present. He based the system on the physical and structural
similarities of organisms. For example, plants are classified based on their
flower structures which showed the shared characteristics of organisms.
Linnaeus named the two-word naming system he developed, binomial
nomenclature, which identifies specific species. Genus is the first word that
defines a group of similar species. The second word, specific epithet, often
describes the characteristic of the organism. For example, the species name
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
of humans in the present time is Homo sapiens, Homo from the genus where
humans are specified and Sapiens which means ‘wise’ in Latin.
TAXONOMIC GROUPS
In Linnaean classification, species are placed in groups within more
inclusive groups. Living organisms are divided into taxa (singular, taxon).
The taxa range from having very broad characteristics into much more
specific characteristics.
KINGDOM
ANIMALIA
PHYLUM
CHORDATA
CLASS
MAMMALIA
ORDER
CARNIVORA
FAMILY
PROCYONIDAE
GENUS
PROCYON
SPECIES
PROCYON LOTOR
ORDER
RODENTIA
FAMILY
CAVIIDAE
GENUS
CAVIA
SPECIES
CAVIA PORCELLUS
Figure 1.3 – Raccoon and guinea pig classification
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
As you can see from Figure 1.3, a comparison between a raccoon and
a guinea pig’s taxonomic groups, species is the most specific group. A
genus is a group of similar species. A family is a taxon of similar genera.
An order is a taxon of similar families. A class is a taxon of similar orders. A
phylum is a taxon of similar classes, sometimes described as division. A
kingdom is a taxon of similar phylum or phyla. Lastly, a domain is a taxon
of similar kingdom.
PHYLOGENETIC
CLASSIFICATION:
relationships determined?’
‘How
are
evolutionary
In phylogeny, evolutionary relationships are determined based on
structural similarities, breeding behaviors, geographical distribution,
chromosomes, and biochemistry. Structural similarities are the physical
features that species have in common. Breeding behavior is used to
compare species in a certain habitat. An example is how two groups of frogs
have a difference in their mating behavior in a lake. An organism’s
geographical distribution shows how a particular species is related to other
species because of their ancestry. It tells us how the first specific species of
an organism have evolved to different species because they moved to new
environment through time which helped them adapt. Chromosome
similarity is used to prove that two organisms that may not seem to look
alike are related. Lastly, biochemistry is used to determine evolutionary
relationships. Scientists study the DNA of species and find that closely
related species have similar DNA sequences and, therefore, similar proteins.
Sometimes these biochemical studies reveal that species once thought to be
closely related are not.
Molecular systematics is the discipline that uses data from DNA and
other molecules to determine evolutionary relationships.
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
I.
Morphology and Molecular Homology
Homology is the phenotypic and genetic similarities due to
shared ancestry. Morphological homology is the similarity of the
internal structure of an organism to a common ancestor with the similar
structure. On the other hand, molecular homology is how the genes
or DNA sequences are homologous and descended from sequences
brought by a common ancestor.
Hence, organisms that has very similar morphological and
molecular homology been likely to be more closely related than
organisms that has vastly different structure or genes.
Figure 1.4 – Lynx versus Bobcat.
Even though lynxes and bobcats
seem similar because of their
appearances, they are very different
in structure. For an instance, a lynx
hips are higher than a bobcat’s, plus
the lynx ear tufts is pointier and long.
These have led to the conclusion that
both species came from a common
ancestor.
II.
Analogy vs. Homology
Since homology identifies that species from a common ancestor
is related because of their similar structures and DNA sequences –
analogy, on the other hand, indicates that even though the organisms’
structures being studied looks similar, it does not mean they are closely
related with each other. An example is how flying organisms like bats
are identified as mammals, and birds are proven to be related to
dinosaurs.
Molecular homoplasy describes that even though two
organisms’ have very similar DNA sequences bases, it does not mean
that they are closely related.
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
You should know that to infer phylogeny, homology must be
distinguished from analogy.
CLADISTICS
Cladistics is a method or system based on the classification system.
Taxonomists who use cladistics assume that as groups of organisms evolve
from a common ancestor, they keep a unique inherited trait. This is where
scientists attempt to place species into groups, clades.
Clades are nested within larger clades like taxonomic groups.
However, a taxon is equivalent to a clade only if:
It is monophyletic, which signifies that it consists of an ancestral
species and all its descendants.
It is paraphyletic, which consists of ancestral species and some, but
not all, of its descendants.
It is polyphyletic, which includes taxa with different ancestors.
As a result of descent with modification, organisms both share
characteristics with their ancestors and differ from them. A shared ancestral
character is a trait originated in an ancestor of the taxon. However, a shared
derived character is an evolutionary novelty unique to a clade. As an
example, in mammals, backbone is a shared ancestral character because
all mammals have backbone, but it does not distinguish them from
vertebrates because the latter all have backbones. On the other hand, hair
is a shared derived character because it is shared by all mammals but not
found in their ancestors.
Figure 1.5 – Shared ancestral and shared derived characters (mammals)
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
MOLECULAR CLOCK VS. NEUTRAL THEORY
To determine the timing of molecular phylogenies that extend beyond
the fossil record, biologists relied on the concept about how change occurs
at a molecular level called molecular clock.
The concept of molecular clock is a yardstick for measuring the
absolute time of evolutionary change based on the observation that some
genes and other region of genomes appear to evolve at constant rates.
However, in the 1960s, several scientists independently published
papers about neutral theory, which describes that much evolutionary
change in genes and proteins has no effect on the fitness and therefore is
not influenced by natural selection.
FIVE-KINGDOM SCHEME VS. THREE-DOMAIN SCHEME
Most of us know that early scientists classified organisms into two
kingdoms: plants and animals. However, in the late 1960s, many biologists
have organized and recognized a five (5) kingdom scheme.
The 5 kingdoms consist of Monera (prokaryotes), Protista (unicellular
organisms), Plantae, Fungi, and Animalia. This scheme highlighted the two
fundamentally types of cell, prokaryotic and eukaryotic, and set the
prokaryotes apart from all eukaryotes by placing them in their own kingdom,
Monera.
However, phylogenies based on genetic idea soon began to reveal a
problem with this system: Some prokaryotes differ as much from each other
as they do from eukaryotes. Such difficulties have led biologists to adopt a
three (3) domain scheme.
The three domains consist of: Bacteria, Archaea, and Eukarya. They
are a taxonomic level higher than the kingdom level.
The domain Bacteria contains most of the currently known
prokaryotes, including the bacteria closely related to chloroplasts and
mitochondria.
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
The second domain, Archaea, consists of a diverse group of
prokaryotic organisms that inhabit a wide variety of environments.
The third domain, Eukarya, consists of all the organisms that have
cells containing true nuclei. This domain includes many groups of singlecelled organisms, as well as multicellular plants, fungi, and animals.
The three-domain system highlights the fact that much of the history of
life has been about single-celled organisms. The two prokaryotic domains
consist entirely of single-celled organisms, and even in Eukarya, only the
branches plants, fungi, and animals are dominated by multicellular
organisms.
Figure 1.6 – The three-domain system – Bacteria, Archaea, and Eukarya.
Cain, M. L. (2011). Phylogeny and Tree of Life. In Campbell Biology (9th ed., p. 552). San Francisco,
California: Pearson Benjamin Cummings.
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Basic Taxonomic Concepts and Principles, Description,
Nomenclature, Identification, and Classification
REFERENCES:
Cain, M. L. (2011). Phylogeny and Tree of Life. In Campbell Biology (9th ed., pp. 536-553). San
Francisco, California: Pearson Benjamin Cummings.
Glencoe. (2011). Organizing Life's Diversity. In Reading Essentials for Biology (pp. 184-193).
Columbus, Ohio: The McGraw-Hill Companies.
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