Down Syndrome Research Paper
Genetic Project: Down Syndrome
What is Down Syndrome?
Down Syndrome is a chromosomal disorder where a child is born with an extra partial or full chromosome 21, thus leading to the over-expression of many genes present on this extra chromosome. Therefore, it is neither dominant nor recessive. Down Syndrome affects about 1 in 700 babies born, making it one of the most common genetic birth defects in the United States. There are actually 3 different types of Down Syndrome, Trisomy 21 (Nondisjunction),
Translocation, and Mosaicism. Down Syndrome is most commonly caused by an error during cell division that is called “nondisjunction”. During or before conception, a pair of 21st chromosomes do not separate in either the sperm or the egg. The result of this is an embryo with …show more content…
3 copies of chromosome 21 instead of the normal 2. The extra chromosome is then replicated throughout the entire body as the embryo develops. A different type of Down Syndrome is called Mosaicism.
Mosaic Down Syndrome makes up about 1% of all cases of Down Syndrome. A child with mosaic Down Syndrome has 2 different groups of cells, some with the normal 46 chromosomes and some with 47, possessing an extra chromosome 21. This can occur in 1 of 2 ways, one way is through a nondisjunctional event during the mitosis, after conception. As the first few cells undergo mitosis, one of them fails to split its chromosomes equally, resulting in a daughter cell with an extra chromosome 21. This daughter cell goes on to replicate, resulting in a whole line of cells with an extra chromosome 21. Because one of the daughter cells had an extra chromosome 21 there is another daughter cell without chromosome, however, because of its missing chromosome this cell rarely survives or replicates. The other way that Mosaicism can occur involves 2 events of nondisjunction. The first event occurs when an egg or sperm cell is made, this leads to an egg or sperm cell with 24 chromosomes and an extra chromosome 21. The next nondisjunctional event happens after conception. As the cells are dividing the extra chromosome 21 is lost in one of the cells resulting in a cell with 46 chromosomes. As the cells
replicate the end result is some cells with 46 chromosomes and some with 47. The last last form is Translocation Down Syndrome accounting for around 4% of cases. In these cases there are three 21 chromosomes, however, one of them is attached to another chromosome, often chromosome 14. These cases are the only ones in which Down Syndrome can be hereditary, the translocation is hereditary in about ⅓ of these cases. It is known that maternal age has an effect on the chance of having a child with Down Syndrome. A 20 year old woman has 1 in 2,000 chance of having a baby with Down Syndrome, a 30 year old woman 1 in 900 and a 40 year old woman has a 1 in 100 chance. There are no known environmental factors or causes of Down Syndrome.
What is Down Syndrome?
Down Syndrome is a chromosomal disorder where a child is born with an extra partial or full chromosome 21, thus leading to the over-expression of many genes present on this extra chromosome. Therefore, it is neither dominant nor recessive. Down Syndrome affects about 1 in 700 babies born, making it one of the most common genetic birth defects in the United States. There are actually 3 different types of Down Syndrome, Trisomy 21 (Nondisjunction),
Translocation, and Mosaicism. Down Syndrome is most commonly caused by an error during cell division that is called “nondisjunction”. During or before conception, a pair of 21st chromosomes do not separate in either the sperm or the egg. The result of this is an embryo with …show more content…
3 copies of chromosome 21 instead of the normal 2. The extra chromosome is then replicated throughout the entire body as the embryo develops. A different type of Down Syndrome is called Mosaicism.
Mosaic Down Syndrome makes up about 1% of all cases of Down Syndrome. A child with mosaic Down Syndrome has 2 different groups of cells, some with the normal 46 chromosomes and some with 47, possessing an extra chromosome 21. This can occur in 1 of 2 ways, one way is through a nondisjunctional event during the mitosis, after conception. As the first few cells undergo mitosis, one of them fails to split its chromosomes equally, resulting in a daughter cell with an extra chromosome 21. This daughter cell goes on to replicate, resulting in a whole line of cells with an extra chromosome 21. Because one of the daughter cells had an extra chromosome 21 there is another daughter cell without chromosome, however, because of its missing chromosome this cell rarely survives or replicates. The other way that Mosaicism can occur involves 2 events of nondisjunction. The first event occurs when an egg or sperm cell is made, this leads to an egg or sperm cell with 24 chromosomes and an extra chromosome 21. The next nondisjunctional event happens after conception. As the cells are dividing the extra chromosome 21 is lost in one of the cells resulting in a cell with 46 chromosomes. As the cells
replicate the end result is some cells with 46 chromosomes and some with 47. The last last form is Translocation Down Syndrome accounting for around 4% of cases. In these cases there are three 21 chromosomes, however, one of them is attached to another chromosome, often chromosome 14. These cases are the only ones in which Down Syndrome can be hereditary, the translocation is hereditary in about ⅓ of these cases. It is known that maternal age has an effect on the chance of having a child with Down Syndrome. A 20 year old woman has 1 in 2,000 chance of having a baby with Down Syndrome, a 30 year old woman 1 in 900 and a 40 year old woman has a 1 in 100 chance. There are no known environmental factors or causes of Down Syndrome.