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| Down's Syndrome |
You might know or have seen somebody with Down's syndrome but in this article, you're going to learn what it is and why it happens. A change in DNA causes Down syndrome. you probably remember that any change in the structure or the amount of DNA of an organism is called a mutation.
Mutations such as certain chemicals or ultraviolet light cause mutations. if a mutation occurs in a somatic or bodily cell, only that cell and its cells will be affected. if a mutation occurs in sexual self or germ cells and fertilization occurs, then every cell in the embryo or fetus and baby will carry that mutation. this is what happens with Down's syndrome.
Humans usually have 23 pairs of chromosomes 46 in total 44 autosomes and two sex chromosomes. sex cells are produced in the type of cell division called meiosis or reduction division. in humans, meiosis produces four daughter cells that each have 23 chromosomes half the number of a somatic cell. however sometimes the chromosomes are not separated or divided up how they should be and this is called nondisjunction.
One example of nondisjunction in humans is the condition known as Down syndrome. in this case, the 21st chromosome fails to segregate and the gamete produced possesses 24 chromosomes 23 plus an extra copy of chromosome 21. the fusion of this gamete with a normal one results in the offspring having 47 chromosomes.
So what are the consequences of having an extra chromosome for people with Down syndrome? well, the difficulties vary in severity. the facial characteristics can include a flattened broad face and narrowed eyes but people with Down syndrome don't all look the same. they also look after their parents and family.
People with Down syndrome may have a lower than average IQ and a shorter than average life expectancy. some conditions more common in people with Down syndrome include problems with the heart and bowel difficulties with hearing and vision and a higher risk of infections. however, everybody who has Down syndrome may be affected in different ways.
Pablo Pineda for example, a Spanish actor who won a silver shell award at the San Sebastian Film Festival was also the first person with Down syndrome in Europe to get a university degree. he now has two nondisjunctions does occur with other chromosomes but these usually result in miscarriage. this is less likely to happen with a 21st chromosome because it is relatively small. the Down syndrome mutation appears to occur in the production of over rather than sperm and its incidence increases with the age of the mother.
The chance increases from approximately one in several thousand in a teenage mother to one in a hundred in a 40-year-old mother. in some countries, people who are pregnant are offered diagnostic genetic testing for Down syndrome. this can be done by blood tests or amniocentesis which involves taking a sample of the amniotic fluid surrounding the fetus in the uterus and looking at the number of chromosomes in those cells to see if any have the extra chromosome 21 for Down syndrome having the tests may be the choice of the parents and will allow them to be more prepared for a baby with Down syndrome or choose to have an abortion.
In Iceland this type of genetic screening is widespread and people are counseled when they have the test. most choose abortion which means that nobody is born with Down syndrome in Iceland. what do you think about this?
The estimated incidence of Down syndrome is about 1 in 1000 births worldwide. there are about 15,000 births per hour in the world. so how many people are born with Down syndrome each day in the world pause the article while you work it out. so now you know a little more about what Down syndrome is. what causes it and just how common it is.