One end of each loop is thinner (thin end) than the other end (thick end).
There is extensive RNA synthesis at the thin end of the loops, while there is little or no RNA synthesis at the thick end.
Phase-contrast and fluorescent micrographs of
Sex Chromosomes: females XX, males XY
Females have two copies of every X-linked gene; males have only one.
How is this difference in gene dosage compensated for? OR
How to create equal amount of X chromosome gene products in males and females?
Levels of enzymes or proteins encoded by genes on the X chromosome are the same in both males and females
Even though males have 1 X chromosome and females have 2.
G6PD, glucose 6 phosphate dehydrogenase, gene is carried on the X chromosome
This gene codes for an enzyme that breaks down sugar
Females produce the same amount of G6PD enzyme as males
XXY and XXX individuals produce the same about of G6PD as anyone else
In cells with more than two X chromosomes, only one X remains genetically active and all the others become inactivated.
In some cells the paternal allele is expressed
In other cells the maternal allele is expressed
In XXX and XXXX females and XXY males only 1 X is activated in any given cell the rest are inactivated
1940’s two Canadian scientists noticed a dark staining mass in the nuclei of cat brain cells
Found these dark staining spots in female but not males
This held for cats and humans
They thought the spot was a tightly condensed X chromosome
Barr bodies represent the inactive X chromosome and are normally found only in female somatic cells.
A woman with the chromosome constitution 47, XXX should have 2 Barr bodies in each cell.
XXY individuals are male, but have a Barr body.
XO individuals are female but have no Barr bodies.