Question

What are the two different mechanisms where someone could be born with down syndrome? detail is required in order to show how the zygote will have the correct number of chromosomes

Answer 1

Answer :)

In Down’s syndrome, one extra X chromosome is present in the 21st chromosome. This is called a trisomy.

There are two phases where Down’s syndrome can produce. During gametes development, if meiosis I skip the non-disjunction, then one cell will contain 2n +1 chromosomes, and the other sister cell will contain 2n-1. In meiosis II that is undergoing normal, 2n+1 cells will split into two gametes having n+1 numbers of the chromosome. While the other 2n-1 cell splits into n-1.

In the second condition, if meiosis I happen good, the meiosis II bears non-disjunction. After the division in meiosis II, one cell will contain n+1, other cells will contain n-1. The two other gametes from the normal division will have n chromosomes.

After fusion of n+1 with n cell, trisomy occurs in the zygote that makes the Down's syndrome in the child.