Welcome to brain Stuff from how Stuff Works dot com where smart Happens, brought to you by Visa. We all have things we like to think about. Online fraud shouldn't be one of them, because with every purchase, Visa prevents, detects, and resolves online fraud safe Secure Visa. Hi'm marshall Brain with today's question, how can children from the same parents look so different? The DNA of the parents never changes,
so how can there be so much variation. It turns out that there's a system specifically designed to make children different, and we can explore that a little bit today. Every person has a set of chromosomes. Each chromosome contains two halves that join in the middle, so they look like an X. All that a chromosome is, by the way, is two very tightly coiled strands of d N A. The two halves of each chromosome come from the two parents.
One half of the X in each chromosome comes from the mother and the other half comes from the father. The two halves are bonded together at the middle of the X. Each half of the X contains a complete set of genes, so each chromosome actually has two copies of every gene, A sperm and an egg meat to create a new person. The sperm carries one half of the new person's ultimate chromosomes, and the egg contains the
other half. The question then comes down to where does the DNA and the sperm and the egg come from. A person has two of every gene, but when a sperm gets formed or an egg gets formed, it will only contain one of those two genes, but which one? This is where nature does an especially amazing thing. When forming sperm cells, the father's body randomly chooses genes from the two halves of the father's chromosomes. This means that every term cell contains a random mix of the father's
parents genes. The same thing happens when forming eggs. Therefore, each child that a couple produces is a random mix of the genes. That random mixing is why children are so different. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com.