Question

What are two mechanisms that can contribute to gamete formation that leads to Trisomy 21?

Answer 1

Trisomy means presence of three copies of a chromosome.

Trisomy of 21 is the presence of three copies of chromosome number 21.

Mechanisms -

1. Nondysjunction of homologous chromosomes (pair 21) to separate from each other during anaphase 1 of meiosis 1,

OR

Nondysjunction of sister chromatids (of chromosome 21) to separate from each other during anaphase 2 of meiosis 2

(Nondysjucntion is a common event).

2. Duplication of chromosome 21

(A very rare event).

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