Transcript Classification & Phylogeny

CLASSIFICATION
CLASSIFYING THINGS
• All life is found within a layer around the Earth called the
biosphere. The biosphere includes anywhere that life
exists – including the land, water and air. It’s about 16km
thick and accounts for very little of the planet’s actual
mass.
• Biologists estimate that there are between 30 million to
100 million different species within the biosphere, yet,
only 1.75 million have been identified and described.
• Early attempts at classification were based on the habitat
of the organism or the type of material produced if the
organism happened to be a plant. These systems had to
be replaced as more and more organisms were
discovered.
• Today we classify organisms according to species. A
species is a group of organisms that share many
physical & physiological traits and are capable of freely
interbeeding (mating) and producing viable offspring.
Linnean Classification
• Swedish scientist
Carolus Linnaeus is the
father of the modern
system of classification
known as binomial
nomenclature.
• This system involves
each organism having a
two-part name.
• The first name is the
genus.
• The second name is the
species name of the
organism.
TAXONOMY
• The science of naming organisms and assigning them to
these groups is called taxonomy.
• The categories that are used to classify living things are
called taxa (singular = taxon).
• Taxonomy classifies organisms on several different
levels. Starting with the broadest level and working down
to the smallest level we have…
Kingdom
Animalia
Phylum/Division
Chordata
Class
Mammalia
Order
Primates
Family
Hominidae
Genus
Homo
Species
sapiens
HAIL TO THE KINGDOM
• The first two kingdoms to be recognized were
Animalia and Plantae.
• As technology advanced we soon discovered
the kingdoms of Protista, Fungi and Monera.
• The kingdom monera – which are the bacteria –
would later be split into the kingdoms
Archaebacteria and Eubacteria.
• In your notes, list the six kingdoms used in
classification and state the identifying factor(s)
that are unique to each one.
DICHOTOMOUS KEYS
• These keys are used to help classify organisms
based on their structural similarities or
differences.
• The key works by asking a series of “yes or no”
questions about the organisms – you chose
either yes or no and then proceed to the next
question that follows your answer.
• Eventually your answers lead you to an
identification of the organism.
• Create a dichotomous key using several members of
the class. (Remember, it is similar to playing the
game “Guess Who”.)
PHYLOGENY
• Phylogeny is the evolutionary
history of a species or group of
species that share a common
ancestor. We can make links
between different species by
examining their traits – both
structural and molecular – and
examining the similarities and
differences.
• Evidence used when making
phylogenetic connections…
• Embryology – The embryonic
development between many
seemingly “unrelated” species
will show you that we all start
out looking much the same and
then diverge into the various
forms you see in the adult stage
of the organism.
• (Ontology Recapitulates
Phylogeny)
PHYLOGENY
• Homologous Structures –
These are structures that
are similar in terms of
physical structure but may
have very different
functions.
• If you examine the forelimb
of the animals shown here,
you will see that there are
remarkable similarities in
the bone arrangement and
position within the limb.
• They would have gotten
these structures from a
similar ancestor – hence a
historical connection.
PHYLOGENY
• Genetic Similarities – Many of the molecules
that are used in the structures of organisms and
the enzymes that facilitate important reactions in
the body are very similar between species.
• If proteins are similar, they indicate similarities in
the genetic code. (DNA  RNA  Protein)
• Using these similarities, we can establish a basic
relationship between the physical forms of the
various species and how closely they are related
by a common ancestor. We show these
relationships using a phylogenetic tree.
PHYLOGENETIC TREE
DIVERSITY & NATURAL SELECTION
• Why do we have so many different life-forms if we
started out from one common ancestor?
• Environmental pressure…As organisms branch out
and cover the planet, they experience a variety of
different environmental conditions. The organism
must have the traits needed to survive and
reproduce in the environment or they may perish
(nice way to say die).
• Different environments will value different physical
traits – these physical differences become more
emphasized over time. The result is a number of
organisms that are different from one another –
increased biodiversity.
DIVERSITY & NATURAL SELECTION
• According to the widely accepted theory of evolution by
natural selection, the environment decides (selects) which
organisms are going to be a good fit and which are not. The
ones that fit well promote the next generation and those that
don’t fit do not. This is the basic idea behind natural
selection – it is survival of the fittest.
• The theory of natural selection is based on four
observations…
1. All members of a species display a variety of characteristics in their
appearance and behaviour – many of these are inherited variations.
2. The number of offspring produced by individuals in a species exceeds
the number of offspring that will survive to adulthood.
3. Some offspring, because of their individual differences, are better able
to adapt to the conditions of the environment than others.
4. The better-adapted organisms survive more often and will pass on their
characteristics to their offspring and, as a result, the population
changes.
• If none of the members of a species can adapt to the
environment – the species will go extinct.
NATURAL SELECTION
ARTIFICIAL SELECTION
•
•
Artificial selection
occurs when humans
chose the desired traits
within a species and
select which individuals
shall be bred and give
rise to the next
generation.
The humans select the
fit individuals instead of
the environment –
hence the name artificial
selection.
• The dogs below are the
result of people choosing
their traits – not nature.
Reproduction, Genetic Diversity
& Species Survival
• Reproduction is used to produce the next generation of
offspring in a population. A species may reproduce either
asexually or sexually.
• Asexual reproduction involves only one parent organism and
the offspring are genetically identical to the parent (clones) –
there is little diversity within the population.
• Sexual reproduction involves two separate parents and uses
gametes (sex cells) that are formed by the process of meiosis.
• During meiosis, an event known as crossing over occurs in
which the chromosomes reshuffle the genes they carry and
create new combinations.
• Random assortment also occurs which causes the offspring to
have a mix of both maternal and paternal traits.
• When you calculate the number of possible genetic combinations
available in a human, the number reaches roughly 14 trillion
different genetic possibilities.
WHY IT’S GOOD
TO BE DIFFERENT
• Genetic variation is important because of the
environment’s ability to suddenly change. This change
could be in terms of climatic change, introduction of toxin
or disease or an increase in the number of predators.
• When you have great diversity within the species, you
will have a better chance of one of the members of the
species possessing the traits that will enable them to
survive the environmental change and keep the species
alive.
• As these survivors reproduce, more of the population will
have the traits needed to survive as they were inherited
from their parents.
THAT’S ALL I GOT…