Human cells normally contain 23 pairs of chromosomes, for a total of 46 chromosomes in each cell
. A change in the number of chromosomes can cause problems with growth, development, and function of the body's systems. These changes can occur during the formation of reproductive cells (eggs and sperm), in early fetal development, or in any cell after birth. A gain or loss in the number of chromosomes from the normal 46 is called aneuploidy.
A common form of aneuploidy is trisomy, or the presence of an extra chromosome in cells. "Tri-" is Greek for "three"; people with trisomy have three copies of a particular chromosome in cells instead of the normal two copies. Down syndrome (also known as trisomy 21) is an example of a condition caused by trisomy
. People with Down syndrome typically have three copies of chromosome 21 in each cell, for a total of 47 chromosomes per cell.
Monosomy, or the loss of one chromosome in cells, is another kind of aneuploidy. "Mono-" is Greek for "one"; people with monosomy have one copy of a particular chromosome in cells instead of the normal two copies. Turner syndrome (also known as monosomy X) is a condition caused by monosomy
. Women with Turner syndrome usually have only one copy of the X chromosome in every cell, for a total of 45 chromosomes per cell.
Rarely, some cells end up with complete extra sets of chromosomes.Cells with one additional set of chromosomes, for a total of 69 chromosomes, are called triploid
. Cells with two additional sets of chromosomes, for a total of 92 chromosomes, are called tetraploid. A condition in which every cell in the body has an extra set of chromosomes is not compatible with life.
In some cases, a change in the number of chromosomes occurs only in certain cells. When an individual’s cells differ in their chromosomal makeup, it is known as chromosomal mosaicism
. Chromosomal mosaicism occurs from an error in cell division in cells other than eggs and sperm. Most commonly, some cells end up with one extra or missing chromosome (for a total of 45 or 47 chromosomes per cell), while other cells have the usual 46 chromosomes. Mosaic Turner syndrome is one example of chromosomal mosaicism. In females with this condition, some cells have 45 chromosomes because they are missing one copy of the X chromosome, while other cells have the usual number of chromosomes.
Many cancer cells also have changes in their number of chromosomes. These changes are not inherited; they occur in somatic cells (cells other than eggs or sperm) during the formation or progression of a cancerous tumor.
As a genetic expert with a deep understanding of chromosomal abnormalities, let me provide a comprehensive breakdown of the concepts mentioned in the article you shared.
The article discusses various aspects of chromosomal changes, emphasizing the significance of the normal chromosomal count of 46 chromosomes in human cells. A deviation from this number can lead to aneuploidy, which is a condition characterized by an abnormal number of chromosomes in cells.
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Aneuploidy: Aneuploidy refers to any deviation from the usual 46 chromosomes in human cells. This alteration can occur during the formation of reproductive cells (eggs and sperm), early fetal development, or in any cell after birth. Aneuploidy can lead to problems with growth, development, and the functioning of the body's systems.
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Trisomy: Trisomy is a common form of aneuploidy where there is an extra chromosome in cells. The term "tri-" signifies three, indicating that individuals with trisomy have three copies of a specific chromosome instead of the normal two. An example of trisomy is Down syndrome (trisomy 21), where individuals have three copies of chromosome 21, resulting in a total of 47 chromosomes per cell.
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Monosomy: Monosomy is another type of aneuploidy characterized by the loss of one chromosome in cells. "Mono-" implies one, indicating that individuals with monosomy have only one copy of a particular chromosome instead of the usual two. Turner syndrome (monosomy X) is an example, where women usually have only one copy of the X chromosome in each cell, totaling 45 chromosomes.
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Triploid and Tetraploid: Rarely, cells may have complete extra sets of chromosomes. Cells with one additional set (totaling 69 chromosomes) are termed triploid, while cells with two additional sets (totaling 92 chromosomes) are referred to as tetraploid. However, a condition where every cell in the body has an extra set of chromosomes is not compatible with life.
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Chromosomal Mosaicism: Chromosomal mosaicism occurs when an individual's cells differ in their chromosomal makeup. This can result from errors in cell division in cells other than eggs and sperm. For instance, in mosaic Turner syndrome, some cells have 45 chromosomes (missing one X chromosome), while others have the usual 46 chromosomes.
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Cancer Cells and Chromosomal Changes: The article also mentions that many cancer cells exhibit changes in their number of chromosomes. Unlike inherited changes, these alterations occur in somatic cells during the formation or progression of cancerous tumors.
In summary, the article provides a detailed exploration of chromosomal abnormalities, covering trisomy, monosomy, triploid, tetraploid, chromosomal mosaicism, and the association of chromosomal changes with certain medical conditions such as Down syndrome, Turner syndrome, and cancer.
