Human cells normally contain 23 pairs of chromosomes. One chromosome of each pair is your father, your mother the other.
Down syndrome results when one of the three divisions of cells with abnormal chromosome 21 occurs. All three cell division, causing abnormalities of genetic material from chromosome 21 more, which corresponds to the characteristics and developmental problems of Down syndrome. Three genetic variations can cause Down syndrome are:
Trisomy 21. Over 90 percent of the time, Down syndrome is caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 - instead of the usual two copies - in every cell of it. This form of Down syndrome is caused by abnormal cell division during development of the sperm cell or egg.
Mosaic Down Syndrome. In this rare form of Down syndrome children have some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
Translocation Down syndrome. Down syndrome can also occur when part of chromosome 21 should be attached to (another) to another chromosome, before or understanding. Children with translocation Down syndrome have two normal copies of chromosome 21, but also other material from chromosome 21 onto another chromosome. This form of Down syndrome is rare.
There are no known behavioral and environmental factors that cause Down syndrome.
And 'hereditary?
Most of the time, Down syndrome is not hereditary. And 'caused by an error in cell division during development of the sperm egg or embryo.
Translocation Down syndrome is the only way the disease can be transmitted from parents to children. However, only 4 percent of children with Down syndrome have a translocation. And only half of these children inherited one of their parents.
When translocations are inherited, the mother or the father takes the balanced translocation, which means he or she has rearranged a bit of genetic material, but not the extra genetic material. A balanced carrier has no signs or symptoms of Down syndrome, but he or she may happen to children translocation.
The opportunity to spend depends on the translocation of the sex of the parent who carries the rearranged chromosome 21:
If the parent is the carrier, the risk is about 3 percent.
If the mother is the carrier, the risk is 10 to 15 percent.
Down syndrome results when one of the three divisions of cells with abnormal chromosome 21 occurs. All three cell division, causing abnormalities of genetic material from chromosome 21 more, which corresponds to the characteristics and developmental problems of Down syndrome. Three genetic variations can cause Down syndrome are:
Trisomy 21. Over 90 percent of the time, Down syndrome is caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 - instead of the usual two copies - in every cell of it. This form of Down syndrome is caused by abnormal cell division during development of the sperm cell or egg.
Mosaic Down Syndrome. In this rare form of Down syndrome children have some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
Translocation Down syndrome. Down syndrome can also occur when part of chromosome 21 should be attached to (another) to another chromosome, before or understanding. Children with translocation Down syndrome have two normal copies of chromosome 21, but also other material from chromosome 21 onto another chromosome. This form of Down syndrome is rare.
There are no known behavioral and environmental factors that cause Down syndrome.
And 'hereditary?
Most of the time, Down syndrome is not hereditary. And 'caused by an error in cell division during development of the sperm egg or embryo.
Translocation Down syndrome is the only way the disease can be transmitted from parents to children. However, only 4 percent of children with Down syndrome have a translocation. And only half of these children inherited one of their parents.
When translocations are inherited, the mother or the father takes the balanced translocation, which means he or she has rearranged a bit of genetic material, but not the extra genetic material. A balanced carrier has no signs or symptoms of Down syndrome, but he or she may happen to children translocation.
The opportunity to spend depends on the translocation of the sex of the parent who carries the rearranged chromosome 21:
If the parent is the carrier, the risk is about 3 percent.
If the mother is the carrier, the risk is 10 to 15 percent.
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