Classification

Taxonomy is the science of classification. It involves naming and organising organisms into groups based on their similiarities and differences. This make it easier for scientists to identify them. Organisms can only belong to one group at each level. Similar organisms are arranged in large groups (kindom), then similar organisms from the kingdom grouped into the phylum and so on.

• KINGDOM, PHYLUM, CLASS, ORDER, FAMILY, GENUS, SPECIES

SPECIES:- is a group of similar organisms able to reproduce to give fertile offspring. 
Species are given a two word scientific name to enable scientists from different places to communicate without confusion. Because of discoveries the classification system is updated a lot.

Phylogenetics- An organisms evolutionary history. All organisms have evolved from shared common ancestors. Phylogenetics tell us whos related and how closely.

Reasons why its difficult to classify organisms as a species - you cant see their reproductive behaviour because theyre extinct, or they may reproduce asexually and finally there may be practical or ethical issues.

DNA SEQUENCING- The DNA of organisms can be compared by looking at their DNA base sequences. Closely related species will have a higher percentage of of similarity in the DNA base sequence.

DNA HYBRIDISATION- DNA from two different species are separated into strands and mixed together. Where the DNA base sequence is the same (complimentary), hydrogen bonds form between between bases by specific bas pairing. The more that hybridise the more alike the DNA is. Then DNA is heated to separate it out into strands again, the higher the temperature, the more hydrogen bonds formed (so more energy needed to break them).

Comparing amino acid sequence: Proteins are made from amino acids, the sequence of amino acids is coded for by the DNA base sequence. So similar organisms with similar DNA will have mroe similar amino acid sequences.

Immunilogical comparisons: Antibodies will bind to similar shaped proteins, so any protein that is a simialr shape to the antibodies of a specific species then it will bind.

COURTSHIP BEHAVIOUR- Is used by organisms to attract a mate of the same species. It can be something like releasing chemicals, or displays ect. It is species specific, only members of the same species will respond.

The more similar the courtship behaviour, the more closely related the species are.