(excerpted from the GAPS Index http://aspin.asu.edu/geneinfo/karyo.htm)
The chromosomes need to be stained in order to see them with a
microscope. When stained the chromosomes look like strings with light
and dark ‘bands'.1
Each chromosome arm is defined further by numbering the bands, the
higher the number, the further that area is from the centromere.1
A karyotype is an actual photograph of the chromosomes from one
cell. The cells analyzed are usually white blood cells from a regular
blood draw or from a prenatal specimen. After staining the chromosomes
can be seen as banded strings under 1,000 x magnification.1
They are analyzed by specially trained cytogenetic technologists, Ph.D
cytogeneticists, or medical geneticists. ‘Cytogenetics' is a word for
the study of chromosomes.1
After analysis under the microscope a picture (karyotype) is printed.1
Normal Male Karyotype - a female would have two X's instead of an X and Y
In a karyotype the chromosomes can appear bent or twisted. This is
normal and is simply reflecting how they are sitting on the slide.
Chromosomes are flexible structures made up of DNA. The coding order of
that DNA makes up the genes.1
Chromosomes are analyzed during a time in the cell cycle when they
are compact. During other times in the cell cycle the chromosomes
unwind into long strands of DNA. At that time we would not be able to
see them under the microscope.1
If you were to pull out all the chromosomes into long strands of DNA
there would be over 7 feet of DNA in each cell! That's about 80 billion
miles of DNA in the average human adult!1
Sometimes when chromosomes are analyzed a ‘High Resolution Analysis' is
performed. This means the chromosomes are examined when they are a
little longer than a standard analysis. Since they are longer more
bands can be seen. This is usually done when a small deletion or
duplication is thought to be present.1
There are different types of staining that make the chromosomes look
differently. The stain which is used depends on what type of
abnormality cytogeneticists think they might be seeing. This helps to
help clarify the results.1
Karyotype Process
Artists drawing of a karyotype
Sources of information:
* Editorial or supplementary comments from the editors at Genetic Information and Patient Services, Inc (GAPS)
1. Chromosome Deletion Outreach http://members.aol.com/cdousa/intro.htm
2. NetWellness.com http://netwellness.org/healthtopics/idbd
3. adam.com http://oso.adam.com/ency/article/002053.htm
4. adam.com http://oso.adam.com/ency/article/002048.htm
5. American Society of Human Genetics
http://www.ferre.org/newbrow/genetic.html
6. CaF (Contact a Family) http://www.cafamily.org.uk/inherita.html
7. Virtual Hospital http://www.vh.org/Providers/Textbooks/
ClinicalGenetics/AppendixD/AppenDContents.html
8. http://www.mcoexecutives.com/genetic1.htm
9. March of Dimes http://www.noah.cuny.edu/pregnancy/march_of_dimes
/genetics/gcbooklt.html#About Genetics and Inherited Traits
10. http://www.indiaspace.com/pages/genetics.htm
11. USD http://med.usd.edu/som/genetics/curriculum/
1ECHROM3.htm
12. CMGS http://ich.ucl.ac.uk/cmgs/chromabs.htm
13. Palomar http://daphne.palomar.edu/abnormal/
diagnostic_tests.htm |
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Last Updated ( Sunday, 14 November 2004 )
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