3.4.7 Investigating diversity

Genetic diversity within, or between species, can be made by comparing:

• the frequency of measurable or observable characteristics
• this is based on he fact that each observable characteristic is determined by a gene/genes
• it has limitations because a large number of them are coded for by more than one gene (they are polygenic) so they are not discrete but actually vary continuously. It is therefore often difficult to distinguish one from another.
• the base sequence of DNA 
• we can do this because of DNA sequencing
• we can measure the genetic diversity of a species by sampling the DNA of its members and sequencing it to produce a pattern of coloured bands (as each base is tagged with a fluorescent dye). Analysis of these patterns allows us to compare one species with another/the individuals of the same species.
• the base sequence of mRNA
• mRNA is coded for by DNA
• it follows that, since we can measure genetic diversity with DNA, we can measure it with mRNA.
• the amino acid sequence of the proteins encoded by DNA and mRNA
• the amino acid sequence is coded for by mRNA which is coded for by DNA.
• Genetic diversity can therefore be measured by comparing the amino acid sequences of organisms proteins.

Quantitative investigations of variation

Random sampling
There are several reasons why measurements might not be representative of the population. These include:

• sampling bias
• the selection process may be biased
• chance
• individuals by pure chance may not be representative

The best way to prevent sampling bias is to eliminate any human involvement in choosing the samples. This can be achieved by random sampling. For example:

• divide the area into a grid (e.g stretch two tape measures perpendicular to each other)
• use a random number generator to obtain a series of coordinates
• take samples at the intersection of the coordinates

We can minimise chance by:

• using a large sample size
• analysing the data collected using statistical tests

It is important to understand that gene technology has caused a change in the methods of investigating diversity. E.g DNA differences from measurable/observable characteristics has been replaced by direct investigation of DNA sequences.