Table 1.

Characteristics, advantages and disadvantages of the four major vertebrate model organisms

	Chick	Mouse	Xenopus	Zebrafish
Development	Internal (oviduct for cleavage stage)/external	In utero	External	External
Developmental specificity	Early development like mammals (primitive streak)	Mammalian	Metamorphosis	Early development phases quite different to other vertebrates.
Developmental cycle length	22 days	18–21 days	4 days (at 23°C), temperature dependent	2–3 days
Offspring	<10	<10	103	102
Oocyte size (diameter)	2.5 cm	80–100 μm	1.2–1.4 mm	0.7 mm
Maintenance and breeding	Easy but need to obtain laid eggs	Difficult and expensive	Very easy	Very easy
Manipulative embryology	Access through the egg shell (graft, beads implantation)	Only for embryos up to blastocyst stage but need to be re-implanted	Microsurgery, graft, fate mapping	Microsurgery, fate mapping
Genome	Sequenced (1.2 × 109)	Sequenced (3 × 109)	Tetraploid genome not yet sequenced but X tropicalis genome (1.8 × 109) sequenced	Sequenced (1.7 × 109) duplicated genome
Genetics based techniques	Spontaneous mutations, gene silencing (RNAi), electroporation, transgenic animal (lentivirus), ES cells	Electroporation, KO, KI, conditional transgenesis	Gene silencing (MO), gain of functions (injection RNA, protein, DNA), transgenic animal (REMI)	KO, gene silencing and gain of functions as Xenopus embryos but no targeted injections
Screens	Mutation screens (but costly and difficult)	Mutation screens	Pharmacological and mutation screens	Pharmacological and mutation screens
Specific advantages	Chimera	ES cells, iPS	Targeted injections, high resistance to infections	Transparency of embryos
Website		MGI	Xenbase	ZFIN

ES embryonic cells, iPS induced pluripotent cells, KO knock-out, KI knock-in, MO morpholino oligonucleotide, REMI restriction enzyme-mediated insertion