excerpted from the GAPS Index http://aspin.asu.edu/geneinfo/label.htm)
Each chromosome has a p and q arm; p (petit) is the short arm and q
(next letter in the alphabet) is the long arm. Some of the chromosomes
like 13, 14, and 15 have very small p arms. When a karyotype is made
(see below) the q arm is always put on the bottom and the p on the top.
The arms are separated by a region known as the centromere (red in
picture), which is a pinched area of the chromosome.1
 
Variations of the centromere
In 1960 the first meeting to propose a standard system of naming the
chromosomes took place. Since that time this method of describing
chromosomes and chromosome abnormalities has been revised and added to
several times. It has produced an International Standard of Cytogenetic
Nomenclature. This allows one lab to ‘write out' the chromosome
findings. Any other lab will know what they have found without looking
at the karyotype.
Here are some examples:
46,XX - Normal Female Karyotype
46,XY - Normal Male Karyotype
These descriptions say there are 46 chromosomes and that it is a male or female.
46,XX,del(14)(q23)
Female with 46 chromosomes with a deletion of chromosome 14 on the long arm (q) at band 23.
46,XY,dup(14)(q22q25)
Male with 46 chromosomes with a duplication of chromosome 14 on the long arm (q) involving bands 22 to 25.
46,XX,r(7)(p22q36)
Female with 46 chromosomes with a 7 chromosome ring. The end of
the short arm (p22) has fused to the end of the long arm (q36) forming
a circle or ‘ring'
47,XY,+21
Male with 47 instead of 46 chromosomes and the extra chromosome is a 21. (Down Syndrome)
There are literally millions of types of abnormalities. If your child
has a chromosome abnormality the above nomenclature describes exactly
what it is. Ask your genetic counselor, physician, or health care
professional to describe the chromosome abnormality found.
Below are a few of the codes used in the standard nomenclature.
-
add = Addition material of unknown origin
-
del = Deletion
-
de novo = A chromosome abnormality which has not been inherited
-
der = Derivative Chromosome
-
dic Dicentric
-
dup = Duplication
-
fra = Fragile Site
-
idic = Isodicentric chromosome
-
ins = Insertion
-
inv = Inversion
-
i or iso = Isochromosome
-
mar = Marker chromosome
-
mat = Maternal origin
-
Minus sign (-) = Loss
-
mos = Mosaic
-
p = Short arm of chromosome
-
pat = Paternal origin
-
Plus sign (+) = Gain
-
q = Long arm of chromosome
-
r = Ring chromosome
-
rcp = Reciprocal
-
rea = Rearrangement
-
rec Recombinant chromosome
-
rob = Robertsonian translocation
-
t = translocation
-
tel = Telomere (end of chromosome arm)
-
ter = Terminal end of chromosome
-
upd = Uniparental disomy
-
? = Uncertain
It is important to note that most chromosome abnormalities occur as a
accident in the egg or sperm. Therefore every cell in the body would
have the abnormality. Some abnormalities can happen after conception
and individuals can have a mosaicism (some cells with the abnormality
and some without). Chromosome abnormalities can be inherited from a
parent, like a translocation, or be ‘de novo' (new in that individual).
1
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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