Concepts of Biology (BIOL115) - Dr. S.G. Saupe (ssaupe@csbsju.edu); Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Preparing a Karyotype 

            A karyotype is a pictorial representation of an individual's chromosomes.  The chromosomes are arranged into groups according to size, centromere position (metacentric = middle of chromosome; acrocentric = end of chromosome; submetacentric = somewhere between end and middle) and the presence of satellites (small protrusions).  Karyotypes are usually prepared from blood.  The red blood cells (which lack a nucleus and hence, chromosomes) are allowed to settle out and then the white blood cells (which do possess a nucleus) are treated with colchicine.  Colchicine stops mitosis at metaphase (by preventing the formation of microtubules) when chromosomes are spread out for the easiest viewing.  The treated cells are fixed, stained and examined microscopically.  A photograph is taken and enlarged (now done by computer). The chromosomes are cut out and arranged according to a convention, called the Denver classification, that was established by a group of cytogeneticists,   To prepare a karyotype:

1. Obtain a karyotype sheet.
   

2. Cut the chromosomes apart.  Don't cut along the detail of each chromosome, but cut out squares or rectangles each containing one chromosome.   Before cutting, count the chromosomes to ensure you don't loose any.  And, this will be important later.  
   

3. Arrange the chromosomes in order, from largest to smallest.  (Don't tape/glue down yet)
   

4. Match up homologous chromosomes.  Remember they will be of similar length and shape (i.e., centromere position, satellites) and banding patterns.  
   

5. Once the chromosomes have been arranged, tape or glue them down with the centromere on the dotted (longer arms should point down) in their appropriate groups on the sheet provided.  A table of the Denver classification scheme is provided to help you place the chromosomes in their respective groups.   
   

6. Analyze the karyotype.  Is it from a normal male? normal female? individual missing a sex chromosome or autosome? individual with an extra chromosome(s)?  missing a part of a chromosome?