How do we grow from a single fertilized egg into a fully grown person with trillions of cells? Our cells divide, of course!
And it's no mean feat. Each time a cell divides, it must duplicate our 23 pairs of chromosomes and make sure each "daughter" cell ends up with a complete set of genes.
Errors are potentially fatal to the cell. Runaway cell division, which is the hallmark of cancer, is also serious business.
No wonder then that biologists have been studying cell division for as long as they've known about cells.
Over the years, scientists have pieced together a coherent story about how the process unfolds. And now the nonprofit Allen Institute in Seattle has taken advantage of that knowledge to produce a visualization of human cell division suitable for professional scientists and curious amateurs alike. (The computerized visualization above shows the anaphase stage of cell division.)
The institute's model follows the fate of 15 distinct parts of the cell, from the chromosomes themselves to the tiny fibers, called microtubules, that help tug the chromosomes apart during cell division. (The model focuses on the type of cell division called mitosis, which is the duplicating of a cell, as opposed to meiosis, which is the split that results in egg and sperm cells).
The images that result are a composite of 75 representative stem cells derived from human skin cells, says Susanne Rafelski, who works at the Allen Institute for Cell Science.
Each component was flagged with a fluorescent tag so its fate can be followed through the five stages of the cell cycle, starting with cell growth, then DNA synthesis, another phase of growth and two stages during which the cell actually divides and creates two daughter cells.
The parts are color-coded, so you can still keep track of your favorite cell component as the data are merged into a composite cell.
"We're interested in understanding the cell as a whole," Rafelski says. "So the really big picture view is that we want to put the cell back together with all the mechanistic information that we've been gathering over the years now."
These kinds of visualizations are increasingly popular tools for biologists, teachers and the just plain curious. The Allen Institute has explored the technology as it applies to the brain. The Howard Hughes Medical Institute (which is among NPR's financial supporters) has also produced visualizations of the complete brain of a fruit fly, developing mouse embryos and a host of other images geared toward science teachers.
Another pioneering effort is the Visible Human Project, launched in 1994 and updated over the years to display a man and a woman, built at first from CT and MRI scans and ultimately based on images taken from thin slices of the donated bodies. A private company created a computer program to enable anatomy enthusiasts to explore the visible people.
You can contact NPR Science Correspondent Richard Harris at email@example.com.