Water-siphon test. Dr Henry Knipe â and Dr Marcin Czarniecki â et al. The water siphon test may be performed as part of a barium swallow to assess for gastro-oesophageal reflux in a hiatal hernia. It is performed in the supine RPO position with the patient drinking water continuously. The test is said to be positive if there is visible barium reflux in the oesophagus.
In some instances, offspring can demonstrate a phenotype that is outside the range defined by both parents. In particular, the phenomenon known as overdominance occurs when a heterozygote has a more extreme phenotype than that of either of its parents. Indeed, in a few examples, a trait that shows overdominance sometimes confers a survival advantage in the heterozygote (Parsons & Bodmer, 1961).
In a small percentage of cases, a person with Angelman syndrome inherits two copies of chromosome 15 from his or her father (paternal copies) instead of one copy from each parent. This phenomenon is called paternal uniparental disomy.Rarely, Angelman syndrome can also be caused by a chromosomal rearrangement called a translocation, or by a mutation or other defect in the region of DNA that controls activation of the UBE3A gene.any of the characteristic features of Angelman syndrome result from the loss of function of a gene called. UBE3A. People normally inherit one copy of the UBE3A gene from each parent. Both copies of this gene are turned on (active) in many of the body's tissues.