So Turner's syndrome is a chromosomal defect where one of the X chromosomes is missing. For more details visit the [Wikipedia page] (https://en.m.wikipedia.org/wiki/Turner_syndrome).

But I don't understand why missing one X chromosome would be harmful. Given that in normal females one of the two X chromosome inactivated at an early embryonic stage to a Barr body. For more details visit the Wikipedia page on this.

I also learnt that women are less prone to sex-link genetic disorders .

So my queation is why turners syndrome a problem as one of Copy of X chromosome is active in both cases.

  1. What does it mean to deactivate parts of chromosome

3.also I went over an answer for a similar question but it dint mention about why having two copies of gene essential ? As only dominant of those get expressed.


Short answer
Some genes on the X chromosome escape X-inactivation. Two copies of these genes are needed for normal development. These genes are also present on the Y chromosome. Hence, healthy males and females both have two copies of these genes. In Turner's, the SHOX gene seems to be one of the culprits, which is needed for normal skeletal development.

It appears that both of the X chromosomes are needed for normal development in females, as some genes on the X chromosome escape X-inactivation. Many of these genes are located at the ends of each arm of the X chromosome in areas known as the pseudoautosomal regions. Although many genes are unique to the X chromosome, genes in the pseudoautosomal regions are present on both sex chromosomes. As a result, men and women each have two functional copies of these genes. Many of these genes are essential for normal development (source: Genetics Home Reference).

Which genes on the X chromosome are responsible is not yet known, but a gene called SHOX seems to be involved, which is important for bone development and growth. The loss of one copy of this gene likely causes short stature and skeletal abnormalities in women with Turner syndrome (source: NIH), see Fig. 1.

SHOX is a transcription factor of the homeobox family. It acts during early embryonic development to control the formation of the development of the skeleton. It plays an important role in the growth and maturation of bones in the arms and legs source: NIH).

Fig. 1. Some developmental malformations seen in Turner's syndrome. source: University of Chicago

FYI - I wrote an answer before checking for duplicates. I think my answer does add additional information (the SHOX gene is not mentioned in the linked question's answer

  • $\begingroup$ Hey I modified the question. Kindly review and try to answer $\endgroup$ – sudhanva b Dec 6 '18 at 10:47

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