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Chromosome Disorders
Numerical abnormalities
When cells carry complete extra sets of chromosomes, this is called polyploidy. When there is one extra complete set, to give sixty-nine chromosomes in total, then this is known as triploidy. Two extra sets of chromosomes, to give niney-two chromosomes in total, would be called tetraploidy.
When individual whole chromosomes are missing or extra, this is called aneuploidy. This can happen with any of the autosomal chromosomes (1 to 22) or the sex chromosome (X or Y).
If one extra complete chromosome is present, this is known as trisomy and the number of chromosomes in each affected cell would be 47. The most common disorder arising from a trisomy is Down syndrome (Trisomy 21). Two extra complete chromosomes would be called tetrasomy and the number of chromosomes would be 48. Three extra complete chromosomes would be called pentasomy and the number of chromosomes in each cell would be 49. If a complete chromosome is missing, this is known as monosomy and the number of chromosomes in each cell would be 45.
Examples of aneuploidy involving the sex chromosomes include XYY (male with one extra Y chromosome), XXY (male with one extra X chromosome), XXXY (male with two extra X chromosomes), XXXXY (male with three extra X chromosomes), XXYY (male with one extra X and one extra Y chromosome), XXX (female with one extra X chromosome), XXXX (female with two extra X chromosomes) and XXXXX (female with three extra X chromosomes).
Chromosome abnormalities
| Structural abnormalities 
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