Forward Genetics

This starts with a phenotype and uses this to try and identify and establish the function of the gene that causes it. Instead of knocking the known gene out and looking at the consequences, random mutations are introduced into the genome and the consequences of these on the phenotype produced are examined.

To begin this process a screen needs to be set up in which the expression of a marker gene is induced. Then random mutations are introduced into the genome and interesting phenotypes are selected for analysis.

To identify a gene’s function the techniques used include linkage analysis, expression vectors, epitope tags, and GFP transgenic lines.

Linkage Analysis

The aim in this approach is to find the approximate location of a gene relative to gene marker whose position is already known. A genetic marker is a piece of DNA whose physical location on a chromosome is known. It can be a gene or a piece of DNA with unknown function. The process of linkage analysis is based on the recombination of homologous chromosomes, and it is often used to search for the position of human disease genes. To investigate this in more detail visit the Human Genome site.

Epitope Tags

These are usually composed of amino acids and are used to visualize specific proteins of interest. An example of these are reporter genes which replace the coding sequence of a target gene with a reporter sequence. This is subsequently under the control of the regulatory sequences of the gene. The reporter gene is expressed when gene expression is turned on by these regulatory sequences. The expression of the reporter gene, which replaces the expression of the target gene is then monitored by tracking the enzymatic activity or fluorescence of its protein product. Thus enabling researchers to determine the pattern and timing of specific gene expression. An example of an epitope tag is green fluorescent protein (GFP).

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