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).
Normal Function. The IGF2 gene provides instructions for making a protein called insulin-like growth factor 2. This protein plays an essential role in growth and development before birth. Studies suggest that insulin-like growth factor 2 promotes the growth and division (proliferation) of cells in many different tissues. Although the IGF2 gene is highly active during fetal development, it is much less active after birth.