1.   The mouse is bred with the genetic defect but remains alive, enabling potential cures to be tested out on it.

2.   For centuries, people have bred mutant mice.

3.   Paul Overbeek, who breeds transgenic mice at the Baylor College of Medicine in Houston, found a strain that had more male than female offspring.

4.   The Min mice were bred with a strain that has an inborn shortage of the enzyme methyltransferase, which is needed for methylation to occur.

5.   The researchers bred mice without the gene that makes the protein.

6.   The researchers say they have bred mice missing a gene that bears instructions for making an important brain protein.

7.   Then the transgenic and knockout mice were bred, eventually producing offspring that had all their mouse hemoglobin genes replaced by the mutant human ones.

8.   These carrier mice were bred, Thomas said, and then bred again.

9.   They bred many mice carrying two copies of the klotho gene.