cell fate and lineage
/ sel FAYT and LIN-ee-ij /
Picture a family tree, but instead of people it traces cells: one starting cell divides into two, those divide again, and so on, branching outward until you can point to any cell in the body and trace its ancestry back to the fertilized egg. Cell lineage is that family tree, and cell fate is the question of what each branch eventually becomes.
Precisely, cell fate is the type of cell a given cell will turn into during normal development, and lineage is the ancestral sequence of cell divisions leading to it — the genealogy of a cell. Scientists map these by labeling a cell and following its descendants. Fate can be influenced two broad ways: by what a cell inherits from its mother (intrinsic information) and by signals from its neighbors and surroundings (extrinsic information), and most development blends both.
Cell fate and lineage matter because they turn development from a mystery into something traceable and even predictable. In some animals the lineage is so fixed that biologists have mapped every single division from egg to adult. In humans it is far more flexible and signal-dependent, but the same logic holds: understanding which cell came from where, and what it is fated to be, is the backbone of developmental biology and of efforts to grow specific cell types on demand.
In the tiny worm C. elegans, scientists traced the complete cell lineage: every one of its roughly 959 body cells can be followed back, division by division, to the egg — the first complete cell-fate map of an animal.
A fully mapped lineage: in C. elegans, every cell's ancestry back to the egg is known.
Lineage (where a cell came from) and fate (what it becomes) are related but distinct — in flexible animals like humans, two cells from the same lineage can reach different fates depending on the signals they receive.