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The Study of Genetics

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Probability

You may ask, what does probability have to do with Genetics? Actually it does alot. Probability is the likely hood of a certain trait occurring. For example, if you take a brunnette woman (i.e. BB) and a blond haired man (i.e. bb), chances are the union of the two would produce all brunnette and the offsprings would  be heterozygous. To figure that out, you must use a Punnett Square, which is a diagram.
Step One: Label the couple's alleles on top and on the side:
   b b
B[][]
B[][]
Step Two: You then take the top letter and the letter to the left and put them in the same box:
        b
        |
B--[Bb]
Step Three: Fill in the three remaining boxes:
     b     b
B[Bb][Bb]
B[Bb][Bb]
     Since the dominant allele pair must be BB or Bb, all the offspring will be brunnette. Since there is one lowercase and uppercase letter, they will all be heterozygous!
                                                                                                       
http://www.geometry.net/pure_and_applied_math_bk/probability_page_no_4.html