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Mongolism is a genetic disorder which is caused by the presence of an extra chromosome number
A. 20
B. 21
C. 17
D. 23

Answer
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Hint: Mongolism is the other name of Down’s syndrome. Down’s syndrome is a genetic disorder. Down’s syndrome has received its name because of the characteristic epicanthic eye fold. This kind of fold is typically observed in the Asian population.

Complete answer:
Down's syndrome is a result of the trisomy of chromosome twenty one. This means that the person with Down’s syndrome will have three chromosome number twenty one where normally there are two. The reason for this trisomy is the faulty division of the sperm or the egg cell. The defect during the development of the gametes results in trisomy that is the presence of an extra chromosome.
There are three types of Down’s syndromes -
-Mosaic Down’s syndrome
-Translocation Down’s syndrome
-Trisomy twenty one

The clinical symptoms that a patient of Down’s present with are short stature, cognitive degradation, delayed development, speech problem, brachycephaly, low set ears, obstructive sleep apnea.
Also, a Down’s syndrome patient may have esophageal atresia and transesophageal fistula. Twenty to thirty percent of patients die during the first year of their life. The most frequent cause of death in a Down’s patient is a respiratory infection.

Hence, the correct answer is option (B).

Note: There is no way to prevent Down’s syndrome. It can only be diagnosed on a genetic basis. Down’s syndrome being genetic, can’t be cured. The kids with Down’s usually have congenital heart disease. This is the reason they do not live long. But life expectancy has increased these days due to the emergence of modern medicine.