F.I.S.H.
FISH (Fluorescent in-situ hybridization)
The application of multi-coloured FISH has been used for the analysis of both gender determination (a.k.a. sexing), for X-linked recessive disorders (e.g. haemophilia), aneuploidy screening (e.g. Abnormal number of chromosomes) and translocations (e.g. Robertsonian).
X-linked recessive diseases are caused by genetic defects on the X-chromosome and are usually transmitted by women carriers with a 50% risk of having male offspring hemizygous for the condition, hence affected. Therefore by sexing the embryos and transferring only those which are female, there is a 50% of transferring a normal female and a 50% chance of transferring a carrier that will not be affected by the disease.
Chromosome specific colored probes
Multicoloured FISH analysis using probes for X, Y, 18 and 13/21 show that approximately 40% of the oocytes of women over 40 years of age test positive for aneuploidy. There are now recently developed 5-colour FISH chromosomal probes that allow testing for 5 different chromosomes in 4-5 hours.
