Question

Mongolism is
(a) Turner’s syndrome
(b) Klinefelter’s syndrome
(c) Down’s syndrome
(d) Hypothalamic syndrome

Answer 1

Hint: Mongolism disease occurs due to aneuploidy. It is a condition related to the long arm of the 21^{st} chromosomes (autosomal chromosome) . An extra or missing chromosome is the common cause of such types of genetic disorders.

Complete answer:
Mongolism is the most common form of Down syndrome. It occurs due to trisomy 21 (an extra chromosome at the 21^{st} chromosome) , a condition where individuals have 47 chromosomes in each cell instead of 46. Trisomy 21 happens due to nondisjunction, caused by an error in cell division which leaves a sperm or an egg cell with an extra copy of chromosome 21 before or at the time of conception.
- The Down syndrome is named after John Langdon Down, who first described the physical features of Down syndrome in 1866.
- Genetic diseases with extrachromosomal defects are generally found in X, Y, 13, 18, and 21^{st} chromosome.
- The trisomy of the 13^{th} chromosome results in Patau syndrome while in the 18^{th} chromosome results in Edward syndrome.
- At least 1 out of 160 human births is diagnosed with genetic defects.
- Features of Down’s syndrome:
- The average IQ of a young adult diagnosed with Down’s syndrome is 50, which is equivalent to the mental ability of an 8 or 9 year old child.
- The parents are genetically normal while the offspring is abnormal.
- The extra chromosomes at the 21^{st} chromosome are believed to occur by random chance, with no known behavioral activity or environmental factor that changes the probability.
So, the correct answer is, ‘Down’s syndrome.’

Note: Agents that are capable of causing aneuploidy are known as aneuploidogens. Many of the harmful mutagenic carcinogens are aneuploidogens. For example, X- rays may cause aneuploidy by fragmenting the chromosome and disrupting the spindle apparatus. Chemicals such as colchicine (mitotic poison) can also produce aneuploidy by affecting microtubule polymerization (chains formation).