TABLE 7-1 Comparison of Four Model Animals for Genetic Analysis and Humans As a Reference

Animal

Adult Size (cm)

Genome Size (Mb)

Period of Organogenesis (d)

Generation Time (wk)

Experimental Advantages

Nematode (Caenorhabdits elegans)

0.1

97

0.2-0.4

0.4

Convenient forward and reverse genetics, complete genome sequence known, complete description of development available, simplicity, transparency

Fruit fly (Drosophila melanogaster)

0.4

180

0.5-1

2

Most convenient forward genetics, many genetically defined signaling pathways known, extensive knowledge of development

Zebrafish (Danio rerio)

3

1,700

1-4

12

Vertebrate, good forward genetics, transparency, external, well-studied development, accessible to test chemicals in water

Mouse (Mus musculus)

6

3,000

6-15

10

Placental mammal, closest model to humans, good forward and reverse genetics, well-studied development

For comparison:

 

Human

170

3,500

14-60

27 yr (1,400 wk)

 

Abbreviations: cm, centimeter; d, day; Mb, megabase; wk, week; yr, year.

ablation of specific cells has provided information on inductive cell interactions during embryogenesis and larval growth. This knowledge has been extremely useful in analyzing the genetic control of cell-fate determination and the roles of cell signaling pathways by using genetic approaches, as described further below. For more comprehensive reviews on current knowledge of C. elegans, see Wood et al. (1988) and Riddle et al. (1997).

Transgenic Technologies

DNA Transformation. Cloned genes can be reintroduced into the C. elegans genome by injection of DNA into the syncytial region of the hermaphrodite gonad (Mello et al. 1991). The injected DNA recombines to form large replicating extrachromosomal arrays, which become incorporated into developing oocytes



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