Fate maps and the pattern of cell division: a calculation for the chick wing-bud.

Given the growth rate throughout an embryonic rudiment, one can calculate how its parts must shift as it gets bigger, and so plot fate maps showing their future positions. The calculation is done here for the chick wing-bud from stage 18 to 25, using published data for mitotic index and cell packing density, and new measurements of size and shape. Two main findings are: (1) the wing-bud in this period elongates almost uniformly along its proximo-distal axis. (2) Each limb segment derives from the tissue generated by one cell division cycle in the 'progress zone' at the tip.