Kelly Izlar

The Basics of Chromosome Segregation

Bloom has spent the past five years puzzling over the mysteries of yeast DNA. Yeast cells are similar enough to human cells that biologists can make inferences about human DNA by studying yeast DNA.

Genes, which are segments of helical strands of DNA, build and maintain an organism’s cells. They determine hereditary traits like the shape of a person’s nose and the length of her toes. Each chromosome, basically one long DNA helix wrapped around proteins, is comprised of a string of between 25,000 and 35,000 different genes.

Typically humans have 23 pairs of chromosomes in each cell. When a cell divides into two, all the chromosomes divide and pair off. Each newly created cell contains the same number of chromosomes as the parent cell.

Bloom described this process, which is known as chromosome segregation, using a cooking analogy: “Imagine you have a pot of spaghetti, and you split each of the spaghetti strands in half,” said Bloom. “Your task is to divide that pot in half, but you can’t just take a knife and separate it. You have to make sure each split strand goes to different cells.”

It’s a big, messy job, said Bloom.

“We don’t have a very deep understanding of how it happens,” said Bloom. “We can watch it happen, but that doesn’t tell us how it happens.”

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