Introduction to Cell & Molecular Biology (BIOL121) - Dr. S.G. Saupe (ssaupe@csbsju.edu); Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Karyotypes

    A karyotype is a pictorial representation of an individual's chromosomes.  Click here for an example of a karyotype of a normal female and a normal male.  Note that 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).  The advantage of a karyotype is that it enables a scientist to quickly determine the number of autosomes and sex chromosomes and whether or not the individual is male or female.

    Karyotypes are usually prepared from blood.  The red blood cells (which lack a nucleus and hence, chromosomes) are removed 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 (see below), that was established by a group of cytogeneticists.

Table of Denver Chromosome Classification

Chromosome Group

Chromosome number

Description of chromosomes

A

1 - 3

Large, metacentric

B

4 - 5

Large, submetacentric

C

6 - 12

Medium-sized, submetacentric; X chromosome closely resembles pair number 6, longest in group

D

13 - 15

Medium-sized, acrocentric; all three pairs with satellites on short arm

E

16 - 18

Smallest of the medium-sized; pair 16 metacentric; others submetacentric

F

19 - 20

Short, metacentric

G 

21 - 22

very short; acrocentric; both with satellites

Exercise 1.  Karyotype Analysis
    Obtain a copy of the "Unknown karyotype" and then answer the following questions:

  1. How many total chromosomes does this individual possess?

  2. How many autosomes?

  3. How many sex chromosomes?

  4. Is this individual male or female?

  5. Is this individual normal or show some aneuploiod condition? (missing or with an extra sex chromosome or autosome)

  6. Is this individual missing a part of a chromosome?

Exercise 2.  Karyotype Preparation  

  1. Obtain a karyotype preparation sheet (Click here) and a one of the chromosome karyotype (either karyotype 3, karyotype 6, karyotype 7).  Record the number of the karyotype on the preparation 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.   Answer the following questions:

  • How many total chromosomes does this individual possess?

  • How many autosomes?

  • How many sex chromosomes?

  • Is this individual male or female?

  • Is this individual normal or show some aneuploid condition? (missing or with an extra sex chromosome or autosome)

  • Is this individual missing a part of a chromosome?

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Last updated: July 14, 2009     � Copyright by SG Saupe