Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
The cause of Down syndrome is one of three types of abnormal cell division involving the 21st chromosome. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The three genetic variations that can cause Down syndrome include:
-Trisomy 21. More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells. This form of Down syndrome is caused by abnormal cell division during the development of the sperm cell or the egg cell.
-Mosaic Down syndrome. In this rare form of Down syndrome, children have some cells with an extra copy of chromosome 21, but not all. 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 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 stuck to the translocated chromosome. This form of Down syndrome is uncommon.
There are no known behavioral or environmental factors that cause Down syndrome. As none of these conditions is given by a single gene, but by chromosomal abnormalities, you can't really talk about recessive and dominant: you either have too much genetic material (or abnormally distributed) or you don't!
It is not dominant not recessive because it is not an inherited trait.
Down's Syndrome, or trisomy 21, involves an error in meiosis of the female egg. The error involves a double dose of chromosome 21, which when met with the sperm's donation leads to three chromosomes where there should only be two.
The terms dominant and recessive are reserved for traits our genes normally encode for. This is not a trait, it is an error.
Why isn't the sky a pretty tartan plaid? It just isn't. Down's syndrome is due to having 3 copies of chromosome 21 instead of the usual 2 copies. It is this extra copy which causes the syndrome, making it due neither to dominance nor recessiveness.
its due to a malfunction at meiosis (cell division) that will give an egg 2 chromosomes of chromosome number 21 instead of 1 and when combined with the sperm's 1, you will have 3 chromosomes instead of 2 (trisomy).....
This is completely different to a genetic disease which could be carried on chromosome 21, for instance, but its passed on thru many generations and not just in a single "accident"
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Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
The cause of Down syndrome is one of three types of abnormal cell division involving the 21st chromosome. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The three genetic variations that can cause Down syndrome include:
-Trisomy 21. More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells. This form of Down syndrome is caused by abnormal cell division during the development of the sperm cell or the egg cell.
-Mosaic Down syndrome. In this rare form of Down syndrome, children have some cells with an extra copy of chromosome 21, but not all. 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 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 stuck to the translocated chromosome. This form of Down syndrome is uncommon.
There are no known behavioral or environmental factors that cause Down syndrome. As none of these conditions is given by a single gene, but by chromosomal abnormalities, you can't really talk about recessive and dominant: you either have too much genetic material (or abnormally distributed) or you don't!
It is not dominant not recessive because it is not an inherited trait.
Down's Syndrome, or trisomy 21, involves an error in meiosis of the female egg. The error involves a double dose of chromosome 21, which when met with the sperm's donation leads to three chromosomes where there should only be two.
The terms dominant and recessive are reserved for traits our genes normally encode for. This is not a trait, it is an error.
Why isn't the sky a pretty tartan plaid? It just isn't. Down's syndrome is due to having 3 copies of chromosome 21 instead of the usual 2 copies. It is this extra copy which causes the syndrome, making it due neither to dominance nor recessiveness.
It's more dominant than recessive.
It's not "on" Chromosome 21, it is the result of having three Chromosome 21s.
Genes are dominant or recessive. Down syndrome isn't caused by a gene, it's caused by an extra chromosome in the 21st pair.
its due to a malfunction at meiosis (cell division) that will give an egg 2 chromosomes of chromosome number 21 instead of 1 and when combined with the sperm's 1, you will have 3 chromosomes instead of 2 (trisomy).....
This is completely different to a genetic disease which could be carried on chromosome 21, for instance, but its passed on thru many generations and not just in a single "accident"
Hope this helps...read some of it but it seemed to get real deep real fast. Good luck!