DOWN’S SYNDROME – INTRODUCTION
Down’s syndrome or mongolism is due to a genetic disturbance. Yet in only a few cases is it inherited.
Each cell of the human body contains 23 paired chromosomes on which are carried the genes, those chemical markers which determine who and what we are.
The germ cells, which are the ovum from the female and the sperm from the male, are different.
These cells contain only 23 single chromosomes. When they fuse at conception, the new individual then has 23 pairs, half from the mother, half from the father.
One chromosome, normally termed the X chromosome, determines the sex. A female has two X chromosomes whereas the male has only one X chromosome and a smaller and rather insignificant Y chromosome.
All ova contain X chromosomes but the sperm may have an X or Y and whichever one of these fertilises the ovum determines the sex. In Down’s syndrome there is an extra chromosome usually at number 21.
This is called 21 trisomy.
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