Illustration showing how looking at various manuscripts can help trace the order in which they were produced

Building family trees

DNA sequence analysis is now used to build family trees

It is fairly obvious that, say, rats and mice are closely related. For many years, physical appearance was used to establish family relationships.

Now we know that genes are the units of inheritance, they are used to work out evolutionary relationships. Originally this was based on genes encoding ribosomal RNA sequences, as they are present in all living things. Now, many genes or even entire genomes can be compared.

From a collection of sequences, family relationships can be deduced. A useful analogy can be made with the manuscript copying done by monks in the Middle Ages: sometimes, the monks would make a mistake. The next time the document was copied, the mistake was passed on. By looking at which manuscripts contained which mistakes, researchers can trace the order in which they were produced – the manuscripts’ family tree.

Essentially the same technique is used to draw up family relationships based on gene sequences. This can reveal the relationships between species. It can also provide valuable information about the evolution and spread of bacteria and viruses.

Lead image:

Illustration showing how analysing the mistakes of various manuscripts can help trace the order in which they were produced.

Illustration © Glen McBeth

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in December 2014.

Microbiology, Ecology and environment, Genetics and genomics
Education levels:
16–19, Continuing professional development