Judgment Day: Intelligent Design on Trial

Student Handout

The Chromosome Shuffle

Chromosomes contain all of our genetic code. Humans have 23 pairs of chromosomes that exist in nearly every cell in the body. As part of natural genetic changes over time, chromosomes are rearranged in a number of different ways, including inversions, deletions, translocations, fission, and fusion.

These mutations usually happen during the first prophase of meiosis, when sister chromatids twist around—or cross over—each other, and can lose, gain, or exchange parts to produce the kind of mutations shown here.

Procedure

1. Label the following parts on the chromosome pictured.

   Telomere: At the ends of each chromosome are telomeres that help determine how many times a normal cell divides. Telomeres contain a unique repeating sequence of TTAGGG. Called tandem repeats, these show up 800 to 1,600 times in each telomere.

   Centromere: The constricted region of the chromosome where two sister chromatids are joined and where spindle fibers attach. The centromere is essential for the division of the chromosome in the cell.

   p arm: The p arm is the shorter arm of the chromosome.

   q arm: The q arm is the longer arm of the chromosome.

   The following idiograms—graphic representations of chromosomes—show only one half of the matched chromosome pair.

   
   
   
   

2. Read about each type of mutation below, and then write in the space under each set of chromosome drawings which type of change the drawing depicts. Not all definitions are pictured.

   deletion: A segment of a chromosome is lost. Deletion of a gene or part of a gene can lead to a disease or abnormality.

   duplication: A segment of a chromosome is duplicated on the same chromosome.

   fission: A chromosome piece breaks apart, forming two shorter chromosomes.

   fusion: Two different chromosomes are joined.

   inversion (paracentric): A segment within just one arm (not including the centromere) of a chromosome is turned upside down.

   inversion (pericentric): A segment containing both the centromere region and parts of both arms of a chromosome is turned upside down.

   translocation (reciprocal): Two chromosomes trade pieces with one another.