Can someone explain me Lyon's hypothesis?

Question

Lyon hypothesis is concerning X gene inactivation in human genetic first put forward by Lyon in 1961. I read about it in the text book of Robbins but the explanation didn't hit my head.

Answer 1

To keep it short and simple-

Females have two X chromosomes..one inherited from each parent..(males have one X and one Y)

In case of females...one X chromosome dominates over the other and that means only a single X chromosome can express itself in each cell.The other inactivated X chromosome is seen as a Barr Body in female cell nuclei.

And as only one X chromosome can express in each cell or grop of cells therefore the female body exhibits mosaicism with regards to X chromosome i.e. Sum cells can exhibit the paternal X and some exhibit maternal X chromosome.

Answer 2

Lyon Hypothesis

Answer 3

The original Lyons hypothesis states that only one active X chromosome is required during development of a female child,so the other X chromosome gets inactivated and gets converted into a barr body.Once this X chromosome is inactivated,it remains neutralized.
But the modified Lyons hypothesis states that the X chromosome which has been inactivated can and is reactivated in the germ cells during the first meiotic division i.e does not remain neutralized.
This change was made because if only one X chromosome was required for the development of a female, a subject with 45,X(Turner Syndrome) should have been absolutely normal, which is not the case.
Thus two copies of X chromosome are required for normal development for which the inactivated X chromosome can be reactivated.

Answer 4

For example Ho (The Null Hypothesis): Global warming is not influenced by humans. Ha (The Alternate Hypothesis): Global warming is influenced by humans. This hypothesis can be anything but generally one says it will happen and the other says it wont. Similarly you can have a Hypothesis and A Hypothesis of difference which is the same thing (IE one doesn't change and the other does) What happens is that you test variables based on these hypothesis and accept or reject the hypothesis. If you accept the null you reject the alternate or visa verse. An accepted hypothesis is a theory. A theory becomes more robust when many peers agree with the hypothesis or come to the same conclusion based on similar research. Basically a theory is either a proven sum, formula or it is a generally accepted hypothesis.

Answer 5

The Lyon hypothesis, conceived by Mary F. Lyon in 1961 while she was studying the genetic consequences of radiation exposure, states that in cells with multiple X chromosomes, all but one chromosome is inactivated during mammalian embryogenesis. X-inactivation leads to clumped chromatin termed Barr bodies, which are generally considered inert. This formation of Barr bodies is called Lyonization.

In most mammals, including humans, the X chromosome that is inactivated is determined by chance. In marsupials, however, the paternal X chromosome is always inactivated. Inactivation is achieved by methylation of the X chromosome DNA, a common way in which the cell silences particular genes. Certain animals have their coloring patterns dictated by this phenomenon. For example, female calico cats have unique patterns of fur due to certain areas where different X chromosomes are inactived. The X chromosomes that are activated express different coloring genes and lead to their mosaic fur color.

However, there are now reports that women still express many genes from their inactive X chromosomes, and that different women express different genes from the inactive X. Research by Carrel and Willard (2005) indicates that 15% of the genes on the inactive X chromosome are actually active across all women, and a further 10% of genes were switched on in some women. Many of these genes are dominant genes covering for defective recessive alleles on the active X chromosome to cover such sex-linked disorders as haemophilia and color blindness.

Answer 6

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RE:
Can someone explain me Lyon's hypothesis?
Lyon hypothesis is concerning X gene inactivation in human genetic first put forward by Lyon in 1961. I read about it in the text book of Robbins but the explanation didn't hit my head.

Answer 7

Murray in 1908observed a densely stained patch of chromatin in the cells (nucleus) of females & not in males Latter on Lyon in1961 sugested that there is a barr body in the female cells nucleas A female has 2 Xchrpomosome one of them becomes inactive during early development i.e it becomes hetro chromatic.So only one x chromosome expreeses itself The inactive one stains as a dark patchThis is called Lyon hypothesis It is used to check the sex of people in olampis which are open to one sex only asmales contain no barr bodies

Answer 8

The concept that mammalian females are X-chromosome mosaics as a result of the random inactivation of one X chromosome in some embryonic cells and their descendant and of the other X chromosome in the rest..