X-inactivation

[virajpatel]

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I am reading in various sources that X-inactivation always occurs during embryonic development. But if X is always inactivated then why does it say that females are less likely to display certain sex linked traits than males. The inactivation should make them equal right? I'm so confused by this topic. Please explain.

 

[TheDanger]

In the cells of females, sometimes the X1 chromosome becomes the Barr body and sometimes the X2 chromosome becomes the Barr body. Let's look at a female that is heterozygous for an X-linked recessive disorder (ex: sickle-cell anemia). The sickle-cell chromosome (Xa) is only active/expressed in some cells and it will usually be compensated for by the non-sickle-cell cells (XA), so the female won't have the full blown disorder (or any noticeable symptoms). Some of her RBC may not be perfectly shaped, but they won't be messed up enough to be detrimental to her health. Hypothetically, every single one of her cells could coincidentally have the XA chromosome inactive and then she would have the disorder, but this is incredibly unlikely.

 

[Member 139582]

In most somatic cells of the female, one of the X chroms. condenses, and most of the genes are not expressed. Which one condenses is random, which results in half the cells expressing genes from one chromosome, and half the cells expressing genes from the other chromosome. In Calico cats, only the females have both yellow and black fur.
But the reason why more females are not colorblind, or in general exhibit more sex-linked traits is because in many genes, if half the cells express the dominant allele, the dom. phenotype results.
Hope this helps.