1. SECTIONS:
2. preface & acknowledgements
3. genetics at a glance
4. contacts, support & testing
5. testing & pregnancy
6. newborn screening
7. cancer in the family
8. cardiovascular conditions
9. chromosomal conditions
10. clotting & bleeding conditions
11. cystic fibrosis
12. diabetes
13. fragile X syndrome and other causes of developmental delay
14. haemoglobinopathies
15. hereditary haemochromatosis
16. neurofibromatosis
17. neurological conditions
18. psychiatric conditions
19. genetics in practice
20. emerging genetic technologies
21. glossary

Chromosomal terminology

 

1. The arms of chromosomes are denoted as ‘p’ for the short arm and ‘q’ for the long arm (see Figure 1).
2. The representation of a person’s chromosome complement is referred to as a karyotype. An individual
   may have a normal or abnormal karyotype.
3. A karyotype is written as the total number of chromosomes present followed by the sex chromosome
   composition. For example, a normal male is denoted as 46,XY and a normal female as 46,XX.
4. Changes in whole chromosome number (aneuploidy) are denoted using a ‘+’ or ‘-‘ sign against the
   particular chromosome. For example:
5. Trisomy 21 (Down syndrome) male 47,XY,+21
6. Mosaicism for trisomy 18 female 47,XX,+18/46,XX
7. Turner syndrome 45,X
8. Changes in structure are caused by rearrangements. For example, gain or loss of part of a chromosome,
   eg 5p-syndrome: 46,XY,del(5)(p15), is a deletion of part of the short arm of chromosome 5 with a
   breakpoint at band 15.
9. Translocations are denoted by the letter ‘t’ followed by details of the chromosomes involved,
   eg 46,XY, t(5;17) indicates a male with a reciprocal translocation between chromosomes 5 and 17.
10. Some chromosomal changes have no impact on growth, development or health because there is no net
    change to the genetic information.

 

Figure 1

A diagrammatic representation of a chromosome showing the short (‘p') and
the long (‘q') arms

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