Table 1. . Comparison of model systems.

Organism	Generation time	Cost†/day	Protocol required?	Time to generate gene knockout‡
Mouse	3 months	1$ (per cage)	Yes	3–4 months
Zebrafish	3–4 months	0.6$ (per tank)	Yes	3–4 months (3–4 weeks kd§)
Fruit fly	10 days	Negligible	No	1–3 months
Roundworm	4 days	Negligible	No	1–3 months (2–3 days kd§)
Baker's yeast	90 min	Negligible	No	3–4 days
Bacteria	20 min	Negligible	No	3–4 fays

^†All costs shown in US dollars.

^‡With extant mutant libraries, gene function can be immediately examined.

^§kd: Transient knockdown.