Chromosomes are stick-shaped structures in the middle of each cell in the body. Each cell has 46 chromosomes grouped in 23 pairs. When a chromosome is abnormal, it can cause health problems in the body. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these:.
Meiosis my-OH-sis is the process in which sex cells divide and create new sex cells with half the number of chromosomes. Sperm and eggs are sex cells. Meiosis is the start of the process of how a baby grows. There are many types of chromosome abnormalities. However, they can be organized into two basic groups: numerical abnormalities and structural abnormalities. Numerical Abnormalities: When an individual is missing one of the chromosomes from a pair, the condition is called monosomy.
When an individual has more than two chromosomes instead of a pair, the condition is called trisomy. An example of a condition caused by numerical abnormalities is Down syndrome, which is marked by mental retardation, learning difficulties, a characteristic facial appearance and poor muscle tone hypotonia in infancy.
An individual with Down syndrome has three copies of chromosome 21 rather than two; for that reason, the condition is also known as Trisomy An example of monosomy, in which an individual lacks a chromosome, is Turner syndrome. In Turner syndrome, a female is born with only one sex chromosome, an X, and is usually shorter than average and unable to have children, among other difficulties.
Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocation. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere. Inversions: A portion of the chromosome has broken off, turned upside down, and reattached.
As a result, the genetic material is inverted. Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material. Most chromosome abnormalities occur as an accident in the egg or sperm. In these cases, the abnormality is present in every cell of the body.
Some abnormalities, however, happen after conception; then some cells have the abnormality and some do not. 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.
Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice.
Contact a health care provider if you have questions about your health. Can changes in the number of chromosomes affect health and development? Chromosome and Gene Abnormalities. Test your knowledge.
More Content. Some physical defects can be corrected with surgery, but generally treatment is supportive. Was This Page Helpful? Yes No. Cri-du-Chat Syndrome.
Overview of Sex Chromosome Abnormalities.
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