The small zone at the extreme end of an embryo’s limb bud, where all of the activity of building the limb takes place.
Zone of Polarizing Activity (ZPA) Term Timeline in Your Inner Fish
The timeline below shows where the term Zone of Polarizing Activity (ZPA) appears in Your Inner Fish. The colored dots and icons indicate which themes are associated with that appearance.
Chapter 3: Handy Genes
...In the 1990s, scientists were better able to look for the molecular mechanisms that the ZPA uses to differentiate fingers. Cliff Tabin, Andy MacMahon, and Phil Ingham decided to look at... (full context)
...“sonic hedgehog” (named after the video game character). Sonic hedgehog is only active in the ZPA of chicken embryo limbs. After experiments that confirmed that hedgehog does the same limb production... (full context)