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78 CB 1.3 GENETIC VARIATION
USING KNOWLEDGE OF GENETICS
Phylogenetic Trees
A ‘phylogenetic tree’ is a diagram that represents relatedness of organisms. The pattern of
branching not only reflects how related species are but also their evolutionary history.
Traditionally, scientists determined how related species were by comparing how similar they
looked, and how similar their behaviours and habitats were. The major issue with this technique is
that scientists had to actually observe the species. Scientist’s observations were open to different
interpretations, and this often led to disputes among scientists. It also meant that two or more
similar looking species were often clumped together.
Advances in genetic technology means that scientists can now compare genetic markers to
determine relatedness. DNA sequencing of genetic markers allows scientists to determine the
sequence (order) of nucleotides (bases). The sequence of one species can then be compared
to the sequence of another species. Species that are closely related will have a small number of
nucleotide differences. A larger number of differences corresponds to species being less related.
For example, the nucleotide differences between the little spotted kiwi (Apteryx owenii) and the
great spotted kiwi (Apteryx haastii) would be a lot less than the differences between the little
spotted kiwi and a domestic chicken (Gallus gallus domesticus).
These differences in nucleotide sequences can be visualised in a phylogenetic tree.
A
B
C
D
E
1. Refer to the diagram above to determine if the following statements are true or false.
True False
A and B are closely related to each other.
B and C are more closely related than A and B.
E is not related to A, B, C or D.
A, B , C and D are more closely related to each other than E.
A, B, C and D all evolved from the same common ancestor.
2. Outline the disadvantages of using physical observations to determine relatedness. 



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