• Before the emergence of molecular ecology it was very difficult to obtain genetic data from wild populations, and biologists often had to rely on visible polymorphisms. Phenotypic data are useful for many things, although pheno-typic plasticity often obscures the relationships between phenotypes and genotypes.
• The first studies to link molecular genetics and ecology were based on allozyme data. Proteins are encoded by DNA, and therefore reflect some of the variation in DNA sequences. Allozymes provided some of the first population genetics data, and in early studies these data revealed significantly higher levels of genetic variation than had been anticipated.
• Although undoubtedly a major breakthrough, redundancy in the genetic code and relevance to only a small portion of the genome mean that estimates of genetic diversity based on allozyme data will be conservative. Furthermore, collecting samples for allozyme analysis is often problematic.
• Many different types of gene regions exist within a genome, both coding (repetitive and single copy) and non-coding (including introns and pseudo-genes) regions.
• Genetic diversity is generated continually through recombination and mutations, which include slipped-strand mis-pairings, nucleotide insertions/ deletions and nucleotide substitutions.
• These days, laboratories routinely use PCR to selectively amplify specific regions of DNA, a technique that allows researchers to genetically characterize individuals by generating enough copies of a particular segment of DNA to allow subsequent manipulation and characterization.
• Universal and species-specific primers enable researchers to amplify sequences from very small amounts of DNA that can be isolated from a range of samples, including faeces, feathers, hair, leaves and scales; this permits the humane sampling of wild organisms.
• Gel electrophoresis allows us to separate and identify the fragments that are amplified by PCR on the basis of their sizes. DNA sequencing reactions will generate the precise sequences of amplified DNA products.
• The quantities of DNA and RNA in a given sample can be estimated using RT-PCR, a technique that has been used to study gene expression and to estimate both the numbers and identities of species in composite samples such as microbial communities.
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