Molecular Identities Laboratory
Section
What is DNA? DNA (deoxyribonucleic acid) is a long polymer made up of nucleotides, which are composed of a sugar-phosphate group and one of 4 bases: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T). It is the sequence of these 4 bases (ACGT), which comprises the genetic code. This code, with a few exceptions, is the same for all organisms so we can directly compare DNA sequences obtained from species ranging from amoebas to zebras.
In living organisms DNA is not a single molecule but rather a pair of molecules entwined in the shape of a double helix.
The main role of DNA is the long term storage of heritable information. It carries the instructions needed to make the structural components of living organisms eg proteins. The DNA segments that code those instructions are called genes Thousands of genes and millions of bases are organised into structures called chromosomes. The set of chromosomes within a cell is called the genome
Significance
Why do museums have genetics labs?
The answer to that question depends to some extent on what you think when we say “genetics”. While generally museums don’t engage in the type of genetic engineering that lead to the cloning of Dolly the Sheep we do use DNA extensively to complement our fundamental biodiversity research programs in taxonomy and systematics.
Taxonomy is the science of the discovery, description, classification and naming of species. Systematics is an expansion of this work, classifying species according to their evolutionary relationships. Species are traditionally described on the basis their morphology, that is, their internal and external physical features eg their size, number of appendages, skeletal structures, colour patterns, growth forms, scale shape and so on.
There are, however, a number of problems inherent in using morphology. Morphology is influenced to some extent by the environment. Unrelated organisms can independently evolve very similar features as a result of having to adapt to living in similar environments. A classic example is the dorsal fin and torpedo-like body shape of ichthyosaurs (extinct marine reptiles), sharks (fish) and dolphins (mammals). Another issue is that speciation is not always accompanied by morphological changes. Some groups are morphologically “austere”, that is, they lack distinguishing physical characters and in some groups morphology is highly conserved. These issues can lead to 2 or more species being classified as one because they are superficially indistinguishable resulting in what is known as cryptic species.
So how can DNA help? The variability in DNA sequences can provide greater resolution and allow us to identify species objectively. Furthermore, DNA is much less susceptible to environmental influences. By comparing DNA sequences and measuring the number of changes (mutations) between them it is possible to determine if species are closely or distantly related. As a result genetic analyses have now become commonplace in scientific research conducted at museums. DNA does not and will never replace classical morphology based taxonomic studies but works as a valuable complement to them.