Ask A Scientist© Zoology Archive

name annette
status other
age 30s

Question - please can you tell me the meaning of philadelphia chromosone my 
father has CML and also told that he has a problem with the above 
chromosone THANK YOU

The explanation requires some basic genetic knowledge which I will try to
give... hang on!  First, in each of your cells you have 2 sets of 23
chromosomes or 46 chromosomes altogether. One set comes from your mother
and one set comes from your father. When the cells divide, the pairs of
chromosomes line up in pairs together. One of nature's ways of making sure
that none of us ends up alike is to scramble the genetic information at
different points. One way to do this is to have the pairs of chromosomes
exchange pieces. A small part of each breaks off and they trade places.
This is known as crossing over. Every once in awhile, the pieces don't
reattach where they should. In the case of the Philadelphia chromosome, an
accident known as a translocation occurs. A piece of chromsome 9 breaks off
and instead of attaching to the other chromosome 9, it attaches to the end of
chromosome 22. Another thing you must know is that chromosomes are made of
DNA and DNA is the stuff that contains the instructions for making your
body's structures. The information on chromsome 9 that is added to
chromosome 22 changes the message on chromosome 22. Its like adding extra
words to a sentence. In this case, it tells the genes in that area to "make
more white blood cells NOW, and make them FAST!!!!" It actually takes away
control of cell division. I hope this helps. Good luck to your Dad.

Van Hoeck
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The Philadelphia chromosome (named for the city in which it was discovered)
is the name for a particular rearrangement of chromosomes called a
translocation. Humans usually have 23 identical pairs of chromosomes - one
set from mom and one set from dad. The Philadelphia chromosome is a
reorganization of the chromosomes so that the ends of chromosomes 9 and 22
break off and switch places. Unfortunately, the breakpoints of both of
these chromomes fall in the middle of genes called oncogenes. These are
genes that are intended to control the normal growth of cells, but if they
are mutated, can lead to a variety of cancers. One of these genes is
called ABL and, when messed up, causes Chronic Myeloid Leukemia. 90% of
CML patients carry the Philadelphia translocation, and there's a 50% chance
that it can be passed on to their children. A genetic test - blood test -
could be used to see whether you have inherited it.

Researchers have created a mouse equivalent of CML, by injecting tumor
cells into an immune-deficient mouse, and they are currently studying gene
therapy approaches to try to slow progression of the leukemia and maybe
eventually reverse it. But it will be quite some time before that sort of
therapy is available for human patients.
---------
Christine Ticknor
Ph.D. Student
Yale University
New Haven, Connecticut
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The Philadelphia chromosome #22 (named I believe after where it was
discovered) is the chromosome which holds the mutated gene loci that causes
CML. It is actually a " 9/22 reciprocal translocation" meaning that a piece
of the #9 chromosome has broken off and moved onto the #22chomosome and a
piece of the #22 has moved to the #9. In so doing it triggers the cells in
which this happens to become cancerous...that is they lose certain controls
present in normal cells such as when to stop multiplying and where to
remain. To see exactly what this is go to the following site.

http://gslc.genetics.utah.edu/disorders/karyotype/philadelphia.html


Peter Faletra
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