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Crossover Activity: Understanding the random nature of crossover during meiosis.

GenScope File:

It is possible for Jack and Jill to have a baby with two normal hemoglobin genes (the B+ allele) and two normal methemoglobin genes (the M allele), and you're going to do it for them!  This puzzle requires a brand new process, called "crossover" in which genes "jump" from one homologous chromosome to the other.  In this case, it's from one chromosome 11 to the other chromosome 11.

1.      Open up the Sickle Cell file and take a cell from each parent organism using the cell tool.

2.       Before you run meiosis, use the magnifying glass to look at the chromosomes. In the upper right-hand corner of the window, click on the "Crossover" button and then click on "Controlled"; see example below:

3.      Now run meiosis.  GenScope will stop in the middle and give you directions to "click on one of the chromatids." (A chromatid is one half of a pair of identical chromosomes.)  Try this and LOOK VERY CAREFULLY at what happens.  What is happening?

4.       Now see if you can use this tool to create a chromosome that has a B+ allele along with an M allele.  If you can do this, you can MAKE A BABY WITH TWO B+ ALLELES AND TWO M ALLELES!!

When you make the baby, call your teacher over and explain how you did it. 5.       Crossover happens all the time in nature, but it happens randomly. When crossover is on auto it happens randomly -just the way it does in real life.  Click on the "Auto" button under Crossover to make it random.  Now make a baby through meiosis and see if you can figure out what happens.

Hint:  After you set it to Auto, it will be easier to see what is happening if you run the entire animation. To run the entire animation, click on the left hand side of the meiosis scroll bar in the meiosis window.

  6.       Now try it out in the Pedigree Window.  Make a bunch of babies and see whether any of them come up with normal hemoglobin and no blue skin.  When you see that, you'll know you've seen a crossover!
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