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Prenatal diagnosis of a non-fluorescent Y chromosome as characterized by FISH-technique

Currently, Y chromosomal DNA is being used to trace back the origin of our common ancestors. Cytogenetically, the structural variation [polymorphisms] of the Y-chromosome has been classified into three groups. Variation of the long arm is being contributed by fluorescence [Yqf] and non-fluorescent segments [Yqnf] by QFQ staining. The rarest form is a pericentric inversion that is a ‘third type’ of variation. Here, we report a ‘fourth type’ where fluorescent heterochromatic DNA is apparently deleted and could no be detected by QFQ-technique. A 28 years old female was referred for genetic amniocentesis because of her high MSAFP. Her first pregnancy ended in fetal loss after 9-10 weeks of gestation. The cytogenetic findings with QFQ-technique revealed a marker chromosome which was found in his biological father. By FISH-technique using WCP probe [Vysis], it was a Y-chromosome. A small amount of heterochromatic DNA was detected in the fetal Y and the father by the Y cocktail probe [DYZ1\DYZ3, Oncor] which is specific for heterochromatin suggesting that it is not a Yqnf. In addition the presence of telomere on Yq was also noted by the all human telomere probe [Oncor]. Utmost caution should be exercised during post-amniocentesis counseling as earlier claims of dire consequences are unfounded. However, Yqnr chromosome may serve as a phylogenetic treat for molecular anthropologists who are in search of human lineage.