1.   First, the researchers must breed animals that lack both copies of the gene.

2.   Researchers breed programs by trial and error and, voila, something interesting emerges.

3.   Since the Chinese chestnut resists the blight, researchers are breeding a hybrid that is one-sixteenth Chinese and the rest American.

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

5.   To explore the various possibilities, researchers bred the hybrids into three distinct lineages.

6.   When researchers bred mice without the huntingtin gene, they died before birth, Wexler said.

7.   Researchers are now breeding mice that develop cancer naturally.