Development

The polarity problem

Frog polarity

Dorsal polarity in frogs

Summary of the frog results

Insect polarity

Experiments on leaf hoppers

What the experiments mean

Developmental genetics

Christiane Nusslein-Volhard and Eric Wieschaus

The genetic screen

Bicoid

A rescue experiment

Vertebrate homologs

Goosecoid in Xenopus

Goosecoid in zebrafish

Other homologous genes

Hox genes

Conclusion