Down's syndrome in humans is due to

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(B) : Down's syndrome is the trisomy of the $21$st chromosome in humans.Down's syndrome is characterized by short stature,warty skin,protruding tongue

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three copies of chromosome $21$

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(B) : Down's syndrome is the trisomy of the $21$st chromosome in humans.Down's syndrome is characterized by short stature,warty skin,protruding tongue,slanting eyes,and folded eyelids.The affected person's face presents a typical mongoloid look; hence,it is also called mongoloid idiocy.It occurs due to the phenomenon of nondisjunction.Nondisjunction occurs when a pair of homologous chromosomes does not separate during meiosis but migrates to the same pole of the cell,resulting in an uneven number of chromosomes in the daughter cells ($45$ in one and $47$ in the other).This numerical abnormality results in trisomy $(2n + 1)$ and monosomy $(2n - 1)$.Nondisjunction is more common in sex chromosomes.

Column $I$	Column $II$
$(A)$ Autosomal trisomy	$(i)$ Turner's Syndrome
$(B)$ Allosomal trisomy	$(ii)$ Mendelian disorder
$(C)$ Allosomal Monosomy	$(iii)$ Klinefelter's Syndrome
$(D)$ Cystic fibrosis	$(iv)$ Down's Syndrome

List-$I$ (Syndrome)	List-$II$ (Chromosomal abnormality)
$(1)$ Patau's syndrome	$(A)$ $44 + XXY = 47$
$(2)$ Klinefelter's syndrome	$(B)$ $44 + X = 45$
$(3)$ Down's syndrome	$(C)$ $46 + 1 = 47$,Chromosome $13^{th}$
$(4)$ Turner's syndrome	$(D)$ $46 + 1 = 47$,Chromosome $21^{st}$

Similar Questions

The reduction of one pair of chromosomes in humans is due to:

Mongolism syndrome is caused by

Match the Column $I$ with Column $II$:
Column $I$ Column $II$
$(A)$ Autosomal trisomy $(i)$ Turner's Syndrome
$(B)$ Allosomal trisomy $(ii)$ Mendelian disorder
$(C)$ Allosomal Monosomy $(iii)$ Klinefelter's Syndrome
$(D)$ Cystic fibrosis $(iv)$ Down's Syndrome

Identify the given figure and select the correct option.
$\quad\quad\quad P\quad\quad Q$

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