Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis.

Chromosomes are so named because of their ability to take up staining (chroma in Greek means color).

All chromosomes normally appear as an amorphous blob under the microscope and take on a well-defined shape only during mitosis.

It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.

After comparing his work on locusts with Henking's and others, McClung noted that only half the sperm received an X chromosome.

[4] Luke Hutchison noticed that a number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the Fibonacci sequence.

The X chromosome in humans spans more than 153 million base pairs (the building material of DNA).

[citation needed] Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked.

However, recent research suggests that the Barr body may be more biologically active than was previously supposed.

[9] The partial inactivation of the X-chromosome is due to repressive heterochromatin that compacts the DNA and prevents the expression of most genes.

It is estimated that about 10% of the genes encoded by the X chromosome are associated with a family of "CT" genes, so named because they encode for markers found in both tumor cells (in cancer patients) as well as in the human testis (in healthy patients).

[24] Such discoveries helped to explain x-linked disorders in humans, e.g., haemophilia A and B, adrenoleukodystrophy, and red-green color blindness.

X-linked endothelial corneal dystrophy is an extremely rare disease of cornea associated with Xq25 region.

Megalocornea 1 is associated with Xq21.3-q22[medical citation needed] Adrenoleukodystrophy, a rare and fatal disorder that is carried by the mother on the x-cell.

It affects only boys between the ages of 5 and 10 and destroys the protective cell surrounding the nerves, myelin, in the brain.

This disorder causes a once healthy boy to lose all abilities to walk, talk, see, hear, and even swallow.

In July 2020 scientists reported the first complete and gap-less assembly of a human X chromosome.