Sex Chromosome List

Nearly every cell in the normal human body has 23 pairs of chromosomes (46 in total). One copy of each pair is inherited from the mother, the other from the father. The first 22 pairs (autosomes) are numbered 1 to 22. The 23rd pair are the sex chromosomes. Aneuploidy (chromosome abnormalities) occur in 1 of 160 live births and Down's syndrome is the best known of these. Here is a list of recognised chromosomal arrangements. The list was prompted by discovering that one of our sons is XXY and is drawn from Wikipedia. Many of the conditions are quite rare and knowledge about them is in its infancy. They are not hereditary but happen in the early stages of pregnancy. Numbers 3 and 5 in my list are the normal, expected combinations, which most of us have.

1. YY - such babies never survive to term

2. X - a female with Turner syndrome (c 1 in 2000 live births)
3. XX - a female (homogametic sex)

4. XXX - a female with a syndrome (c 1 in 1000 live births)
5. XY - a male (heterogametic sex)
6. XXY - a male with Klinefelter syndrome (c 1 in 500 live births)
7. XYY - a male with a syndrome (c 1 in 1000 live births)
8. XXXY - a male with a form of Klinefelter syndrome (c 1 in 50,000 live births)
9. XXYY - a male with a syndrome (1 in 18-40,000)
10. XX/XY - a very rare condition that often leads to intersex problems