Saturday, April 5, 2008

Finding a Gene on the Chromosome Map

As a scientist, you've noticed that a genetic disorder runs in families, and you want to find the gene responsible for it.

First, you identify a large family, in which some individuals have the disorder, and others don't. After enlisting the family's support and collecting DNA samples from all family members, you're ready to begin looking for the gene. Where do you go from here?

Here's one way to think about genes

blank puzzle What if the genetic information in each family member were like a jigsaw puzzle? Each puzzle piece would represent a set of genes organized in a specific way, similar to a chromosome. Because all humans have the same set of genes, arranged in the same order, every family member would have the same basic set of puzzle pieces. A generic human jigsaw puzzle might look like the picture at the right

But the information carried in genes differs slightly from person to person. This is what makes each of us unique. As a result, the colors of the puzzle pieces would be different between family members. While some relatives might share puzzle pieces of a certain color, other pieces would be different. Only identical twins share the exact same combination of colors and shapes.

What might a family's puzzles look like?

Look at the family of jigsaw puzzles below. Can you see how some of the child's genes are derived from one parent and some from the other parent?

The child receives exactly half of its genetic information from the mother and exactly half from the father.

Looking at things this way, can you see how you might identify a genetic link in paternity suits, where a genetic connection is sought between a child and a possible father? Half of the child's puzzle pieces must be the same as the father's.

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