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The purpose of this site is to give support and information to families who are affected by a chromosome 3 anomaly. Please see member stories in the top toolbar to find a particular chromosome 3 match.

About Chromosomes

Picture of cell with chromosome, nucleus, and DNA
Picture by: Darryl Leja, National Human Genome Research
Institute, NIH

Chromosomes are found in nearly every cell of your body in the nucleus of each cell. Your red blood cells do not have a nucleus and therefore do not have chromosomes in them. The male sperm cells and female egg cells contain only 23 chromosomes each because when they join they normally give one chromosome each to the developing embryo. The other cells in your body have 23 pairs of chromosomes which makes a total of 46 chromosomes in each cell (to see the male and female normal human karyotypes, please see the green box in the left column). Our chromosomes contain our DNA which makes us who we are.

The picture on the right shows a cell with the nucleus and the chromosomes contained in it. Notice that the middle of the chromosome is referred to as the centromere and the ends of the chromosome are referred to as the telomere.

Each person typically has a pair of number 3 chromosomes.  There are two segments in the chromosome, the shorter portion above the centromere is called the "p" arm and the longer portion below the centromere is called the "q" arm (see diagram to the left).  The karyotype name will specify which segment of the chromosome is affected.  Within each segment are bands to label specific areas of the chromosome.

Please see the picture in the left column to view the segments and bands of chromosome 3.

A deletion in a chromosome means that a part or segment of one of the pair of number 3 chromosomes is missing.  It can also be called a partial monosomy.  A monosomy means that there is the presence of only one chromosome instead of the typical pair.

If you see "del" in a karyotype name it means deletion.

Many of our children have what is called an intersititial deletion meaning "within" the chromosome. This would entail two breaks in the chromosome with a segment missing and the remaining segments joining up.

If a segment near the centromere is missing it is called a proximal deletion.

If a segment near the telomere is missing it is called a distal deletion. You may see a "tel" in the karyotype to describe this.

Sometimes there is only one break in the chromosome which is called a terminal deletion meaning that it goes to the end of the chromosome thus the terminology "ter" in the karyotype name (this does not mean the deletion is any worse than the others).

A very small deletion is called a microdeletion.