Elimination of gene
The effect of the absence of a gene can be very informative about the normal
function of the gene. Eliminating a gene (gene knock-out) completely from a
diploid organism requires knocking out both copies of the gene in the cells.
There are a variety of methods for producing gene knockouts in different model
organisms. The methodology for eliminating both copies of a gene in a mouse
is described below. Once a knockout mouse has been produced, questions are asked
about whether the mouse with two mutant copies develops normally or develops
tumors more readily, etc.
In the mouse:
- DNA that has been engineered to contain a mutant copy of the gene is introduced
into special embryonic stem cells (ES cells) that were growing in tissue culture.
- Cells that take up the DNA are tested to find those in which the mutant
copy has replaced one good copy of the gene.
- Cells with one mutant copy are introduced into an early embryo (blastocyst)
that will take up these cells.
- Mice that are born from this manipulation(and contain the one mutant copy
in their germ cells) are mated to each other.
- One in four mice from this mating will contain two mutant copies of the gene.
