Frequency of Down’s syndrome increases when maternal age is

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4.Principles of Inheritance and Variation

normal

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

A

Above $35$ years

B

Below $35$ years

C

During $1^{st}$ pregnancy

D

In mothers of at least $3$ children

Solution

(a) They occur in $1/700$ births in women aged $25$ years or under.

The frequency increases with age to about $1/100$ for women of age $40$ and $1/10$ for women of age $45.$

Standard 12

Biology

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