Реферат: Down Syndrome Essay Research Paper Down Syndrome
Down Syndrome Essay, Research Paper
Down Syndrome or Trisomy 21 as it is also commonly known, is a genetic condition that for many years has been shrouded in fear, darkness & shame. There is absoultely nothing to fear, and there never should be any feelings of shame, it is not the persons fault. The only darkness associated with down syndrome is the ignorance many people have towards it.
Basically down syndrome means that a person has one extra chromosome in each of the milions of cells in their body. Instead of 46 chromosomes persons with down syndrome have 47 chromosomes. The extra chromosome happens at the 21st pair, thus TRISOMY 21. It can and does happen to anyone.
When was down syndrome discovered?
The late 19th century John Langdon Down, an english physician, published an accurate description of a person with down syndrome. It was published in 1866 and earned Down the recognition as “father” of the syndrome.
Throughout the 20th century, advances in medicine & science enabled researchers to investigate the characteristics of people with down syndrome. It was later determined that an extra partial or complete 21st chromosome results in the characteristics associated with down syndrome.
Why is down syndrome referred to as a genetic condition?
The human body is made up of cells, all cells contain a center, called a nucleus, in which genetic material is stored. This genetic material, knowsn as genes, carries the codes responsible for all our inherited characteristics.
Genes are grouped along rod-like structures called chromosomes. Normally, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent.
In down syndrome, however the cells usually contain not 46, but 47 chromosomes, with the extra chromosome being a number 21. This excess genetic material in the form of additional genes along the 21st chromosome, results in down syndrome.
Because 95 percent of all cases of down syndrome oocur because there are three copies of the 21st chromosome, it is referred to as “trisomy 21″.
What causes down syndrome?
Down syndrome is usually caused by an error in cell division called nondisjunction. Nondisjunction is a faulty cell division which results in an embryo with three number 21 chromosomes, instead of two. Prior to it, or at, conception, a pair of number 21 chromosomes in either a sperm or the egg, fail to seperate. As the embryo develops, the extra chromosome is replicated in every cell of the body.
Why nondisjunction occurs is currently unknown, although it does seem to be related to advancing maternal age. About 80 percent of children born with down syndrome are born to women over 35 years of age. This is because younger women have higher fertility rates.
Although nondisjunction can be of paternal origin, this occurs less frequently. Because this error in a cell division is often present in the egg prior to conception, and women are born with their complete store of eggs, it has been postulated that some environmental factors may be implicated in nondisjunction. However, despite years of research, the cause of nondisjunction is still unknown. There seems to be no connection between any type of down syndrome and parents activities before or during a pregnancy.
Mosaicism occurs wen nondisjunction of the 21st chromosome takes place in one of the initial cell divisions after fertilization. When this occurs, there is a mixture of two types of cells, some containing 46 chromosomes & some containing 47. Because of the “mosaic” pattern of the cells, the term mosaicism is used.