Chromosome conditions and pregnancy

Each of our cells needs to have 46 Chromosomes in 23 pairs to constitue a normal genetic make-up. A Chromosomal Condition arises when there is a defect in the number of the chromosomes making up each cell.

An example of a chromosomal condition is Down's syndrome. It usually occurs when an egg or a sperm is being formed and accidentally acquires an extra chromosome. The pairs of chromosomes making up the sperm or unfertilised egg are numbered 1-22 (leaving out the sex chromosomes).

In Down's syndrome, for some reason the baby receives an extra chromosome from either the sperm or the egg, and it is always chromosome number 21 that is the extra one. This means there are three number 21 chromosomes instead of the more usual two in every cell of the baby's body, creating 47 pairs of chromosomes in each cell, instead of the normal 46.


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