Download lesson 3 domains and binomial

Modern Classification
Objectives:• Know what a species is
• Understand the binomial naming system
• Compare and contrast the five-kingdom
and three-domain classification system.
What is a
species?
Species
• the smallest basic taxonomic unit used to
define living organisms
• a group of individuals
– with similar key features but show variation
– they are usually able to interbreed and produce
fertile offspring
BUT: this definition does not take into account
simple organisms that reproduce asexually
Same species?
Equus ferus
Equus ferus
Canis lupus
Canis lupus
Equus africanus
64
62
Equus ferus
63
Ligers?!
• Hobbs (male) from Sierra Safari Zoo
• Hobbs, with a mane like a lion, the long body of
a tiger, and more mass than either, is a striking
animal.
• He exhibits traits of both parents, his mother
was a Bengal tigress and his father an African
lion.
• He roars like a lion and swims like a tiger.
http://www.sierrasafarizoo.com/animals/liger.htm
• Breeding a male
donkey to a
female horse
results in a mule
• Breeding a male
horse to a female
donkey produces
a hinny.
http://www.imh.org/imh/bw/mule.html
Binomial naming
• Animals are referred to by their genus
and species. For example:
Hippopotamus
Hippopotamus amphibius
Lion
Panthera leo
Giraffe
Giraffa camelopardalis
Nearest common
ancestor of the
Ocelot, the lion
and the tiger
Family
Felidae
Binomial System
Genus
Genus
Leopardus
Species
pardalis
Panthera
Species
leo
Nearest
common
ancestor of
the lion and
the tiger
Species
tigris
Binomial nomenclature
• Conventions in writing scientific names
– Made up of genus and species name
– Genus name starts with a capital letter
– Species name all in small letters
– If writing by hand: underline
– If typing: use italics
Binomial nomenclature of wild flowers
Common name
Scientific name
Red clover
Herb robert
Cut-leaved cranesbill
Trifolium pratense
Geranium robertianum
Geranium dissectum
Meadow thistle
Cirsium dissectum
1. In addition to writing the name in italics, what other
convention is used for scientific names?
2. What genus does red clover belong to?
3. What is the species name of meadow thistle?
4. Which two plants are most closely related:
a) Meadow thistle and cut-leaved cranesbill
b) Herb robert and cut-leaved cranesbill?
Advances in
Classifying
Organisms
Recall: Five Kingdom System
Plantae
Fungi
Protoctista
Prokaryotae
Animalia
Eukaryotic cells
Multicellular
Eukaryotic cells
Unicellular
Prokaryotes
• However some animals are unrelated but
have evolved similar adaptations to
their environment due to convergent
evolution
• So would it be more accurate to DNA
type them?
Organisms and the DNA
percentage they have in common
with humans!
Cat: 90%
Cow: 80%
Mouse: 75%
Fruit Fly: 60%
Banana: 50%
The table shows the percentage
difference between the coding DNA of humans,
chimpanzees, gorillas and orangutans
1.
Which two animals
appear to be most
closely related?
2. Which two are most
distantly related?
3. Explain why these data
cannot provide us with
firm guidelines about
whether humans and
chimpanzees should be
placed in the same
genus.
% difference in DNA
Humans and
chimpanzees
0.87
Humans and
gorillas
1.04
Humans and
orangutans
2.18
Chimpanzees and
gorillas
0.99
Chimpanzees and
orangutans
2.14
Gorillas and
orangutans
2.25
Answers
1. Humans and chimpanzees
2. Gorillas and orangutans
Answer to Q3
•
•
•
There is no clear definition of what a genus is
and what criteria should be used for placing
different species in the same genus.
If we use DNA sequences in this way, there is
no agreement about whether it is more valid
to look at every part of the DNA in a species
or whether we should concentrate on
particular areas, such as the coding
We can also question whether sheer numbers
of differences in DNA bases can justifiably
be used to determine classification, or
whether we should take into account their
effects as well.
Evidence from molecular studies of RNA has now led
to another reassessment of the classification system,
with Woese proposing the 3 Domain System in 1990.
3 Domain System
Bacteria
Archaea
Eukaryotae
5 Kingdom System
Prokaryotes
Protoctists
Fungi Plants Animals
The Three Domain system
• All prokaryotes look the same but they
have different metabolic and biochemical
pathways
• Taxonomists decided to split the
kingdoms creating 3 domains:
Bacteria
Archaea
Eukaryotes
The domains are larger than the kingdoms
The 3 domain system of classification
• groups organisms mainly based on differences in
rRNA structure
• organisms classified into 3 domains and 6 kingdoms
• The domains are Archaea, Bacteria, and Eukarya.
• The kingdoms are Archaebacteria (ancient bacteria),
Eubacteria (true bacteria), Protoctista, Fungi, Plantae,
and Animalia.
• The Archaea and Bacteria domains contain prokaryotic
organisms that do not have a membrane bound nucleus.
• Eubacteria are classified under the Bacteria domain and
archaebacteria are classified as Archaeans.
• The Eukarya domain includes eukaryotes (organisms with
membrane bound nucleus). This domain is further
subdivided into the kingdoms Protoctista, Fungi, Plantae,
and Animalia.
Why was reclassification necessary?
Eubacteria
Archaea
Eukaryotae
Different cell
Similar cell membrane
membrane structure
structure
Different flagella
Similar flagella structure
structure
Different form of RNA Same form of RNA polymerase
polymerase
No proteins bound to
Proteins bound to genetic
genetic materials
material
Different mechanism
Similar mechanisms for DNA
for DNA replication
replication and building RNA
and Building RNA.
Discuss whether the five-kingdom and the
three-domain classifications are completely
different from one another, or if they could
possibly be used together.
Answer
• The three domains are the highest taxa.
• It is possible to have the domain Eukarya,
with the kingdoms Protoctista, Fungi, Plantae
and Animalia as subdivisions of it.
• However, we cannot keep the kingdom
Prokaryota, as that is now split at a higher
level.
Other points for classifying
organisms together
Cytochrome C
• This is a protein used in respiration in all
living organisms (except chemosynthetic
organisms).
• It is made from a sequence of amino acids.
which varies slightly from species to
species.
• If the sequence is very similar between
two species, we can infer that they are
quite closely related.
• We could also compare DNA or RNA
sequences between organisms as opposed
to amino acid sequences.