Lyon hypothesis

hypothesis /hy·poth·e·sis/ (hi-poth´ĕ-sis) a supposition that appears to explain a group of phenomena and is advanced as a basis for further investigation.

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alternative hypothesis  one that is compared with the null hypothesis in a statistical test.

biogenic amine hypothesis  the hypothesis that depression is associated with deficiency of biogenic amines, especially norepinephrine, at functionally important receptor sites in the brain and that elation is associated with excess of such amines.

jelly roll hypothesis  a theory explaining the formation of nerve myelin, which states that it consists of several layers of the plasma membrane of a Schwann cell wrapped spirally around the axon in a jelly roll fashion.

lattice hypothesis  a theory of the nature of the antigen-antibody reaction which postulates reaction between multivalent antigen and divalent antibody to give an antigen-antibody complex of a lattice-like structure.

Lyon hypothesis  the random and fixed inactivation (in the form of sex chromatin) of one X chromosome in mammalian cells at an early stage of embryogenesis, leading to mosaicism of paternal and maternal X chromosomes in the female.

null hypothesis  the particular one under investigation, which frequently asserts a lack of effect or of difference.

one gene–one polypeptide chain hypothesis  a gene is the DNA sequence that codes for the production of one polypeptide chain. Antibodies are an exception; separate genes for variable and constant regions are rearranged to code for a single polypeptide.

response-to-injury hypothesis  one explaining atherogenesis as initiating with some injury to the endothelial cells lining the artery walls, which causes endothelial dysfunction and leads to abnormal cellular interactions and initiation and progression of atherogenesis.

sliding filament hypothesis  the stretching of individual muscle fibers raises the number of tension-developing bridges between the sliding contractile protein elements (actin and myosin) and thus augments the force of the next muscle contraction.

Starling's hypothesis  the direction and rate of fluid transfer between blood plasma in the capillary and fluid in the tissue spaces depend on the hydrostatic pressure on each side of the capillary wall, on the osmotic pressure of protein in plasma and in tissue fluid, and on the properties of the capillary walls as a filtering membrane.

wobble hypothesis  one describing how a specific transfer RNA (tRNA) molecule can translate different codons in a messenger RNA (mRNA) template. It states that the third base of the tRNA anticodon does not have to pair with a complementary codon (as do the first two) but can form base pairs with any of several related codons.

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Lyon hypothesis

n.

The hypothesis that one X-chromosome is inactive during interphase in normal females and is represented in interphase cell nuclei as the sex chromatin body.

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Lyon hypothesis

[lī′ən]

Etymology: Mary L. Lyon, English geneticist, b. 1925

a hypothesis stating that only one of the two X chromosomes in a female is functional, the other having become inactive early in development. Either the maternal or the paternal X chromosome may be inactivated in any given cell. Therefore an X-linked trait may be expressed by some cells and not by others.

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Lyon hypothesis

the random and fixed inactivation (in the form of sex chromatin) of all X chromosomes in excess of one in mammalian cells at an early stage of embryogenesis, leading to mosaicism for X-linked genes in the female, since the paternal X chromosome is inactivated in some cells and the maternal one in the remainder.