How children from the same parents look so different?

Every person has a set of chromosomes, or coiled strands of DNA. Check out this HowStuffWorks podcast to learn how chromosomes combine to promote variation from one generation to the next.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how Stuff Works dot com
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(00:23):
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

(00:47):
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.

(01:07):
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

(01:29):
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

(01:50):
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

(02:12):
of the genes. That random mixing is why children are
so different. Do you have any ideas or suggestions for
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