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Down's Syndrome

Frequency of ...

Question

Frequency of Down's syndrome increases when the maternal age is

A

Above 35 years

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B

Below 35 years

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C

During 1st pregnancy

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D

In mothers of at least 3 children

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Solution

The correct option is A Above 35 years
When maternal age crosses 35, there are more chances of non-disjunction of chromosomes during gamete formation. This results in genetic disorders.

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Why is it that the chance of having a child with Down's syndrome increases if the age of the mother exceeds 40?

Q. Chromosomal abnormalities occur during meiosis, a process that produces gametes (eggs and sperm) within human bodies. Abnormalities occur when there is an uneven split of chromosomes into each gamete. The following table shows 6 of the most common syndromes associated with chromosomal abnormalities.

\begin{matrix} Syndrome name & Chromosome Affected & Incidence per 10,000 births & Type of mutation Polyploidy & Extra complete set of chromosomes & Fatal, doesn't reach full term & Addition Patau syndrome & 13 & 2 & Addition Edwardsn syndrome & 18 & 3 & Addition Down syndrome & 21 & 15 & Addition Klinefelter syndrome & 23 & 10(affects only males)) & Addition Turner Syndrome & 23 & 2(affects only females)) & Deletion \end{matrix}

(I) Following 30,000 of all births, how many children would be predicted to have Turner syndrome?
(a) 0
(b) 3
(c) 4
(d) 6

(II) From above mentioned table, what is the sex chromosome makeup of a child with Klinefelter syndrome?
(a) XO
(b) XY
(c) XXY
(d) XX

(III) The incidence of Down’s syndrome increases with maternal age, and not significantly with paternal age. What may reasonably explain this trend?
(a) Failure of muscular contractions to correctly fuse the two gametes.
(b) Gradual accumulation in germ-line chromosomal mutations throughout reproductive age.
(c) Maternal oocytes have a longer period of meiosis than paternal spermatozoa, and thus, there are more opportunities for mutations to develop.
(d) Maternal mitochondrial DNA is mutated in Down’s syndrome.

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