Question

What Is the source of the extra chromosome 21?

Answer 1

Extra chromosome 21:

1. Down syndrome is a genetic abnormality caused by an extra copy of chromosome number 21, making it a chromosomal disorder.
2. Down syndrome (2n+1) is caused by an additional chromosome number 21, which results from abnormal cell division.
3. Chromosomes are duplicated during normal cell division, and each daughter cell receives a copy of each chromosome. Sometimes these chromosomes are unable to separate properly, resulting in unequal chromosome division in each daughter cell. This is referred to as chromosome non-disjunction.
4. Because of this chromosome non-disjunction, daughter cells receive an abnormal number of chromosomes, i.e. one cell receives one chromosome 21 while the other receives an extra chromosome 21.
5. In most cases, the extra copy of chromosome 21 is inherited from the mother in the egg. The extra copy of chromosome 21 is passed down from father to son in a small percentage of cases (less than 5%).