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Speaker 1: with today's question, how can children from the same parents
Speaker 1: look so different? The DNA of the parents never changes,
Speaker 1: so how can there be so much variation. It turns
Speaker 1: out that there's a system specifically designed to make children different,
Speaker 1: and we can explore that a little bit today. Every
Speaker 1: person has a set of chromosomes. Each chromosome contains two
Speaker 1: halves that join in the middle, so they look like
Speaker 1: an X. All that a chromosome is, by the way,
Speaker 1: is two very tightly coiled strands of d N A.
Speaker 1: The two halves of each chromosome come from the two parents.
Speaker 1: One half of the X in each chromosome comes from
Speaker 1: the mother and the other half comes from the father.
Speaker 1: The two halves are bonded together at the middle of
Speaker 1: the X. Each half of the X contains a complete
Speaker 1: set of genes, so each chromosome actually has two copies
Speaker 1: of every gene, A sperm and an egg meat to
Speaker 1: create a new person. The sperm carries one half of
Speaker 1: the new person's ultimate chromosomes, and the egg contains the
Speaker 1: other half. The question then comes down to where does
Speaker 1: the DNA and the sperm and the egg come from.
Speaker 1: A person has two of every gene, but when a
Speaker 1: sperm gets formed or an egg gets formed, it will
Speaker 1: only contain one of those two genes, but which one?
Speaker 1: This is where nature does an especially amazing thing. When
Speaker 1: forming sperm cells, the father's body randomly chooses genes from
Speaker 1: the two halves of the father's chromosomes. This means that
Speaker 1: every term cell contains a random mix of the father's
Speaker 1: parents genes. The same thing happens when forming eggs. Therefore,
Speaker 1: each child that a couple produces is a random mix
Speaker 1: of the genes. That random mixing is why children are
Speaker 1: so different. Do you have any ideas or suggestions for
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Speaker 1: this and thousands of other topics, go to how stuff
Speaker 1: works dot com.