Fine structure genetics
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Fine structure genetics is a subfield of genetics which encompasses a set of tools used to examine not just the mutations within an entire genome, but can be isolated to either specific pathways or regions of the genome. Ultimately, this more focused lens can lead to a more nuanced and interactive view of the function of a gene.
Similar to forward genetics, regional mutagenesis seeks to saturate with insertions or point mutations, but instead of for the entire genome, it saturates only a small portion of the genome. By limiting the region in focus, researchers are then able to intensify the number of mutations within any genes or promoters within that regions, often illuminating more complicated functions than could be identified with a broader focus. Furthermore, such mutations can show how the specific structure of that region of a chromosome affect expression levels and function.[1]
Such mutations are introduced in the same means as forward genetics, often through chemical induction or transposable element insertions. The creation of specific balancer chromosomes that are restrictive to only a small region of the genome can guarantee that mutations will only be isolated and reproduced only in that region.[1]
Modifier Screens
When a gene is identified as affecting a specific phenotype, a modifier screen can be used to assess which genes that either enhance or inhibit the phenotypic expression of the initial mutation. This is a powerful way of rapidly identifying many genes that are involved in the expression of a phenotype, but such screens can only say whether or not two genes interact, not what their exact function are, or how they relate. For instance, the product of the second gene may interact directly with that of the first gene, or it may be involved in distantly on the pathway.[1]
One of the major benefits of modifier screens is that screens do not necessarily have to take place in the organism of interest. For instance, a gene that corresponds to an important phenotype in an organism in which a set of screens involving mutagenesis (i.e. human beings), will often have a homologue in a model organism. In this case, that homologous gene can either be knocked out or the initial gene can be ectopically expressed in the model organism, at which point a screen for modifiers of the aberrant phenotype can take place.[1]