the hypothesis that gene dosage imbalance between males and females, because of the presence of two X chromosomes in females (XX) as opposed to only one in males (XY), is compensated for by random inactivation of one of the X chromosomes in the somatic cells of females. The inactivated X chromosome becomes the Barr body (see sex chromatin). [M. F. Lyon (1925–2014), British geneticist]
The statistical hypothesis that one variable has no association with another variable or set of variables, or that two or more population distributions do not differ from one another. In simplest terms, the null hypothesis states that the results observed in a study, experiment or test are no different from what might have occurred by chance alone.... null hypothesis
A supposition that appears to explain a group of phenomena and is advanced as a basis for further investigation; a proposition that is subject to proof or to an experimental or statistical test. Studies are often framed to test a ‘null’ hypothesis (for example “subjects will experience no change in blood pressure as a result of administration of a test product”) to rule out every possibility except the one the researcher is trying to prove, an assumption about a research population that may or may not be rejected as a result of testing. A null hypothesis is used because most statistical methods are less able to prove something true than to provide strong evidence it is false. See also “theory”; “null hypothesis”.... hypothesis
Health Encyclopedia