why does the down syndrome usually carry from female gamete? and why does the probability increase...

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Question

why does the down syndrome usually carry from female gamete? and why does the probability increase by maternal age? thx~

Answer 1

Answer #1

Non-disjunction may occur due to- unable to pair, synapse, or cross-over during prophase of meiosis, failing to align during metaphase, or improper or failure to separate or dis-join during anaphase and telophase.
Down’s syndrome results due to such non-disjunction usually during meiosis I.
The condition is due to trisomy of chromosome 21 (or three copies of chromosome 21).
Translocation, leading to chromosome 21 remaining attached to another chromosome (usually chromosome 14) may also lead to Down’s syndrome.
The rate of non-disjunction is more in oocyte than observed in the spermatocytes.
Down’s syndrome has been associated with the age of the female parent. It is observed that the risk of having Down’s syndrome increases with age of the female (usually above age of 35).
The ovum age is attributed to increased meiotic halt resulting in more trisomy during oogenesis.

Answer 2

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