Down’s syndrome in humans is due to

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(b): Down&rsquo;s syndrome is the trisomy of $21$ stchromosome in man. Down&rsquo;s syndrome ischaracterized by short stature, warty skin, protrudingt

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three copies of chromosome $21$

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(b): Down&rsquo;s syndrome is the trisomy of $21$ stchromosome in man. Down&rsquo;s syndrome ischaracterized by short stature, warty skin, protrudingtongue, slanting eyes, with folded eyelids. The affectedperson&rsquo;s face presents a typical mongoloid look. Henceit is also called as mongoloid idiocy. It occurs due tothe phenomenon of nondisjunction.Non disjunction occurs when a pair of homologous chromosomes donot separate in meiosis but migrate to the same poleof the cell resulting in an uneven number ofchromosomes in the daughter cells $(45$ in one and $47$ in other) This numerical abnormality results in trisomy $(2n + 1)$ and monosomy $(2n -1)$. Nondisjunctionismore common in sex chromosomes.

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