The type of chromosomes carried in the human sperm cell determine the sex of the baby that will develop from the fertilized egg. Each egg carries an X chromosome. A sperm may carry either an X or a Y chromosome. If an X-bearing sperm fertilizes the egg, a female results (XX). A male is formed when a Y-bearing sperm fertilizes the egg (XY).

When biologists wish to study human chromosomes, they sometimes photograph the chromosomes through a microscope. After these photographs are enlarged, the chromoomes are cut out and arranged in pairs. The resulting product is called a karyotype.


Human Male Karyotype and Human Female Karyotype

1. Construct a karyotype from the chromosomes shown on the next page. Cut out the individual (doubled) chromosomes and match up the pairs. Then arrange the pairs from longest to shortest as shown above. The last step is to number the pairs.

2. How many pairs of chromosomes are there in the human cells?

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3. Is the karyotype you made that of a male or a female?

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4. How can you tell?

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These pages authored and maintained by Marcella Dawson. Revised 3/2002 . Copyright 1995 CRPC GirlTECH. All rights reserved. . Email your comments. These pages were developed through GirlTECH '96, a teacher training and student technology council program sponsored by the Center for Research on Parallel Computation (CRPC), a National Science Foundation Science and Technology Center.