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Diversity of organisms

Binominal system

(Two names)

The binominal system

Ovis canadensis

Ovis gmelini

Ovis aries

Genus: a group of species that share common characteristics but may not be able to interbreed.

Species: a group of organisms in the same genus that are able to interbreed to produce fertile offspring.

Naming rules

Taraxacum officinale or dandelion

A red kangaroo, Macropus rufus.

  • Genus name starts with a capital (upper case) letter.
  • Species name starts with a lowercase letter.
  • Genus name is always written before the species name.
  • The complete name, i.e. genus and species, should be word processed in italics, or underlined when handwritten.
  • Often genus and species names are written using Latin or classical Greek because they are unchanging languages, however there are many other sources of binomial names.

Binominal system

System of names for species is universal (used by all) and has been agreed and developed at a series of congresses. Each time a new species is discovered, it is given a scientific name using the binomial system.

Different species?

Morphology

Individuals of the same species share more morphological characteristics than members of different species.

Biological species concept

A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring.

Chromosomes??

What does the chromosomes tell us

Karyogram from Karyotyping

What about this one?

Hypothesis: at some point chromosomes 12 and 13 of the great ape karyotype fused, creating what is now chromosome 2 in the human karyotype.

Evidence:

  • The genes of chromosome 2 closely match those of the two suspected fusion chromosomes in chimpanzees.
  • Telomeric DNA, repetitive sequences found at the ends of chromosomes where they help protect the ends of the chromosome from damage, were found at the suggested fusion region of chromosome 2.
  • There is a second centromere region, the site where the cell’s cytoskeleton attaches to the chromosome during cell division, but this one has mutated and does not function.

When?

Before these two left us...

But....

Genome

Comparing genomes

Genome:

All of the genetic information of an organism.

Within a species there is usually only single-nucleotide polymorphisms (SNPs) that contribute to variation and diversity.

Genome size

Genome sequencing

The process of determining the order of the bases in an organism’s genetic code.

Dichotomous keys

Dichotomous key

"A series of paired opposing statements which guide the user to the identity (or allows the classification) of an item or organism."

Dichotomous key

5.3.S1 Construction of dichotomous keys for use in identifying specimens.

Dichotomous key

Taxonomy

HL

Taxonomy

There are also many intermediate taxa, such as subfamilies and superorders

Humans in taxonomy

Advantages

The perspective of classification has shifted from a system based on similarities in appearance and behaviour, to a more precise and detailed one based on amino acid sequences++

1. It reflects the evolutionary relationships among different organisms

2. It reflects the process of evolution

3. It can be used to make predictions about the characteristics of organisms

4. It helps us to understand the diversity of life on Earth

The three domains

Phylogenetic tree

Cladogram

Cladistics

HL

What is a clade

"A group of organisms that have evolved from a common ancestor"

Definitions

Clade: A group of organisms, both extant and extinct that share an ancestor.

Cladistics: A system of classifying organisms according to shared characteristics, based on ancestry.

Cladistics: A system of classifying organisms according to shared characteristics and geneteic evidence, based on ancestry.

Cladogram: A diagram that shows the evolutionary relationship of a group of organisms.

Remember:

Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.

Cladograms are representations of when divergence of species into clades occurred along the evolutionary chain

Things to remember (1):

Convergent evolution vs Divergent evolution

Things to remember (2):

Homologous structures vs Analogous structures

What to use?

Molecular clock

"A figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged."

"There is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. That is, the longer the time period since the two species separated, the more differences there will be when the DNA of the two species is compared."

The conversion of differences in base sequence to units of geologic time usually needs to be checked against the fossil record.

Example

If a particular mitochondrial gene accumulates base sequence mutations at a rate of 3 every 5 million years, about how long ago would two species have shared a common ancestor if their gene base sequence differs by 13 bases?

If you know that 3 mutations occur per 5 million years, then 1 mutation occurs per 5/3 million years.

So, 13 mutations occur over 13 × 5/3 million years = 21.7 million years.

The two species would have shared a common ancestor around 21.7 million years ago.

Calibration point

The oldest fossil of a specific species that is known to exist can be used

Example for use of cladogram

Cladogram

Outgroop

Root

Node

Terminal branch : Extant species

Analysis of cladograms

1. The branching pattern is assumed to represent the evolutionary relationship between species.

2.If extinct species are included, information must be given on whether the cladogram is based on morphology only because DNA generally is not available for the analysis, although there are some exceptions to this.

3. The more nodes there are between species, the more distant their relationship.

4. Mutations at the DNA and protein level are assumed to occur at a constant rate. For example, 1 base change per 109 years – this may seem like a long time, but remember there are billions of bases in genomes.

5. Some cladograms are drawn to scale, that is the length of the branches is proportional to the time since divergence.

Classification of all organisms into three domains using evidence from rRNA base sequences

Classification

Classification

5.3.A1 Classification of one plant and one animal species from domain to species level

You need to know two!!!

5.3.A2 Recognition features of bryophyte, filicinophyta, coniferophyta, and angiospermophyta.

Angiospermophytes

Filicinophytes

Coniferophytes

Bryophytes

Bryophytes

Angiospermophytes

Filicinophytes

Coniferophytes

5.3.A3 Recognition features of porifera, cnidarian pletyhelmintha, annelida, Mollusca, arthropda and chordata.

A

N

I

M

A

L

I

A

Annelida

Mollusca

Cnidaria

Porifera

Platyhelminthes

Arthropoda

Chordata

5.3.A4 Recognition of features of birds, mammals, amphibians, reptiles and fish

Phyllum Chordata

Chordata is a large phylum of animals that includes the vertebrates together with tunicates (sea squirts) and lancelets. They are distinguished by the possession of a notochord at some stage during their development.

Fish

Aves (Birds)

Amphibia

Mammalia

Reptilia

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