One becomes two
Show on a big screenHow does a body grow from one cell to trillions? A trillion is a million million. One cell becomes two. Each of those becomes two more, and so on.
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The rule
A body grows because its cells keep dividing, one into two. Daughter cells are the new cells made when a cell divides. A chromosome is a thread-like bundle of DNA. Reproductive organs are the body parts that make sperm and egg cells.
Mitosis makes two daughter cells with the same DNA as the parent. Meiosis makes four cells with half the chromosomes. Meiosis happens only in reproductive organs.
Mitosis builds new cells for growth and repair. Meiosis makes gametes, the sperm and egg cells. A sperm and an egg join, and the full chromosome count returns.
- One cell holds one set of instructions.
- It copies them, so there are two full sets.
- It splits into two cells, one set in each.
- Both get a full set.
Which one?
Skin cells divide by mitosis to heal a cut. Healing needs cells just like the old ones. Meiosis would give cells with half the chromosomes.
Try the lab to finish this lesson.