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Speaker 1: Welcome to brain Stuff from how Stuff Works dot com

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Speaker 1: where smart Happens, brought to you by Visa. We all

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Speaker 1: have things we like to think about. Online fraud shouldn't

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Speaker 1: be one of them, because with every purchase, Visa prevents, detects,

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Speaker 1: and resolves online fraud safe Secure Visa. Hi'm marshall Brain

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Speaker 1: with today's question, how can children from the same parents

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Speaker 1: look so different? The DNA of the parents never changes,

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Speaker 1: so how can there be so much variation. It turns

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Speaker 1: out that there's a system specifically designed to make children different,

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Speaker 1: and we can explore that a little bit today. Every

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Speaker 1: person has a set of chromosomes. Each chromosome contains two

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Speaker 1: halves that join in the middle, so they look like

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Speaker 1: an X. All that a chromosome is, by the way,

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Speaker 1: is two very tightly coiled strands of d N A.

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Speaker 1: The two halves of each chromosome come from the two parents.

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Speaker 1: One half of the X in each chromosome comes from

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Speaker 1: the mother and the other half comes from the father.

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Speaker 1: The two halves are bonded together at the middle of

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Speaker 1: the X. Each half of the X contains a complete

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Speaker 1: set of genes, so each chromosome actually has two copies

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Speaker 1: of every gene, A sperm and an egg meat to

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Speaker 1: create a new person. The sperm carries one half of

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Speaker 1: the new person's ultimate chromosomes, and the egg contains the

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Speaker 1: other half. The question then comes down to where does

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Speaker 1: the DNA and the sperm and the egg come from.

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Speaker 1: A person has two of every gene, but when a

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Speaker 1: sperm gets formed or an egg gets formed, it will

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Speaker 1: only contain one of those two genes, but which one?

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Speaker 1: This is where nature does an especially amazing thing. When

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Speaker 1: forming sperm cells, the father's body randomly chooses genes from

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Speaker 1: the two halves of the father's chromosomes. This means that

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Speaker 1: every term cell contains a random mix of the father's

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Speaker 1: parents genes. The same thing happens when forming eggs. Therefore,

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Speaker 1: each child that a couple produces is a random mix

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Speaker 1: of the genes. That random mixing is why children are

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Speaker 1: so different. Do you have any ideas or suggestions for

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Speaker 1: this podcast? If so, please send me an email at

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Speaker 1: podcast at how stuff works dot com. For more on

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Speaker 1: this and thousands of other topics, go to how stuff

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Speaker 1: works dot com.