| Genetic causes of mental retardation |
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| Chromosomal abnormalities The human body is made up of small cells. |
| These cells can be seen only under a lens (microscope). In each cell there are some parts called chromosomes”. |
| A child gets their chromosomes from their father and their mother. |
As a result, the child gets the characteristics of their parents. In human beings, there are usually 23 pairs of
chromosomes (46 chromosomes in total). Sometimes these pairs do not occur correctly. |
| The resultant absence or excess of chromosomes will often result in some form of mental retardation. |
For example, sometimes - for no known reason - during the union of the male and female cells,
a child may have 3 chromosomes instead of 2 in the 21st pair. |
| This is called Trisomy Twenty-one or Down’s syndrome. |
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| Dominant inheritance |
| The science of genetics has established that certain genes will dominate other genes. |
What this means is that where a dominant gene causing mental retardation is present in one parent (the carrier),
it is likely that the same gene - and therefore the same condition - will be present in the child |
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| Recessive inheritance |
If a gene is not dominant, it is recessive; it means that although members of the family may not exhibit a disorder, the (recessive) gene for that disorder may still be present in their body’s cells. |
If both parents carry the recessive gene, and nature contrives to bring these genes together at conception,
the recessive gene will then become dominant. |
In marriages between relatives (particularly siblings or cousins), there is a greater chance for the children
born out of this marriage to be born mentally retarded as both the husband and wife may carry the defective
recessive gene and then pass it on to their children. |
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Mental Retardation
