Human Chromosomes
This shows the 23 paired chromosomes of a human male. These little bundles of data carry all the genetic information needed to make a complete guy -- a total dude. This is how chromosomes look when they're not replicating -- so the DNA is tightly coiled.
a. Close-up of a pair of chromosomes just before cell division.
b. Here's a view of the whole group of chromosomes, showing their normal form and shape. Note the "Y" chromosome, found on males only.
If you take the double helix of DNA apart, you'll see a complex and sturdy structure. Each DNA strand is composed of a sequence of bases connected on the outside to sugar molecules. These sugars, in turn, are interconnected by phosphate groups. On the inside, the bases are connected to bases on the other side of the strand by non-covalent (hydrogen) bonds. These weak bonds allow the two strands to safely break apart, kind of like a zipper.
This is how DNA separates and forms two duplicate molecules. First, the two strands of the double helix are separated by enzymes. Then, DNA bases (components) found within the cell bind to the original strands. Adenine bonds to thymine, and guanine bonds to cytosine. Enzymes bind the bases to the new strand as it forms. This process creates two double strands of DNA that are identical to the original double-stranded molecule.
Here's how cells divide and multiply, forming two daughter cells from a single parent cell. The identical daughter cells are also identical to the parent cell. (Note: one of Wilmut's key innovations in the sheep cloning story was halting the cell cycle.
Images courtesy of Genentech Corp. Check out their graphics gallery for more cool pics.
Do you dread the thought of sharing the planet with countless copies of anybody rich or powerful enough to hire a biotech lab? Let's get to the thorny question.
Is self-reproduction a good thing?
