Three copies of chromosome-21 in a child with | vedclass

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(B) The correct answer is $B$. Down's syndrome is an autosomal aneuploidy caused by the presence of an extra copy of chromosome-$21$. In this case,the

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Maternal meiosis-$I$

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(B) The correct answer is $B$. Down's syndrome is an autosomal aneuploidy caused by the presence of an extra copy of chromosome-$21$. In this case,the child has $3$ copies of chromosome-$21$,where $2$ copies share the same alleles as one of the mother's chromosomes. If non-disjunction occurs during meiosis-$I$,the homologous chromosomes fail to separate,resulting in a gamete containing both maternal homologs. Since these $2$ chromosomes are identical to the mother's alleles (due to the presence of homologous chromosomes that did not segregate),it indicates that the non-disjunction event occurred during maternal meiosis-$I$.

Column $-I$	Column $-II$
$(P)$ Turner syndrome	$(i)$ Sex chromosome $(2n-1)$
$(Q)$ Down syndrome	$(ii)$ Sex chromosome $(2n+1)$
$(R)$ Klinefelter syndrome	$(iii)$ Autosomal $(2n+1)$

Similar Questions

In which of the genetic disorders does an individual have an overall masculine development,gynaecomastia,and is sterile?

$21$ trisomy in humans causes

Choose the correct answer regarding the following statements:
$(i)$ Sickle-cell anaemia is controlled by three pairs of alleles.
$(ii)$ Trisomy is a chromosomal disorder.
$(iii)$ $47$ chromosomes are present in a person having Turner's syndrome.

Match Column $-I$ with Column $-II$ and select the correct option.
Column $-I$ Column $-II$
$(P)$ Turner syndrome $(i)$ Sex chromosome $(2n-1)$
$(Q)$ Down syndrome $(ii)$ Sex chromosome $(2n+1)$
$(R)$ Klinefelter syndrome $(iii)$ Autosomal $(2n+1)$

In Klinefelter's syndrome,what is generally the set of sex chromosomes?

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