Classification of species (AQA new Unit 2)

Principles of classification and classification summary (made with reference to CGP AQA biology revision guide)

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Principles of classification
Classification: grouping together similar organisms.
Taxonomy (science of classification) makes it easier to identify and study organisms.
Seven levels: Kingdom, Phylum, Class, Order, Family, Genus, Species (group of similar
organisms that can produce fertile offspring).
Phylogenetics: an organism's evolutionary history.
Tells us how closely related species are.
Distinguishing species: e.g. fertile offspring.
Reasons why reproductive behaviour difficult to determine: extinct, asexual reproduction,
practical reasons (geographical), ethical reasons (lab study).
DNA is used to classify.
Classifying Species
Species classification: DNA or proteins
Taxonomic hierarchy based on similarities and diff in their genes
Done by comparison of DNA sequences
Hybridisation: DNA sequencing and hybridisation
Sequencing: order of bases, (G,C, A, T) closely related will have higher percentage in
similarity of base order.
Hybridisation: single strands of 2 different species' DNA mixed together, same base
sequences (specific base pairing) cause hydrogen bonds to form. Heating used to separate
(hotter the temp needed the more hydrogen bonds form ­ therefore more similar DNA)
Proteins: similar organisms will have similar proteins.
Amino acid sequence ­ sequence coded for by base sequence. Similar organisms will have
similar DNA base sequence
Immunology comparisons ­ similar proteins will bind the same antibodies.
Interpreting data: On DNA and protein similarities
If data % - higher percentage = more similarities
Amino acid sequences ­ similar sequences = similar organisms.
Courtship behaviour: each species has specific behaviour
Used to attract mate of the same species. E.g. use of chemical or displays
Species specific ­ each species have own call and response pattern so mating will only ensure
if both partners same species.
The more closely related a species the more similar their courtship behaviour.


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