Posted 18 March 2006 - 01:10 PM
So what does sex-linked inheritance actually mean?
Well, because the Y chromosome in males is different from the X along most of its length, males are effectively haploid for X-chromosome genes, and as a result , recessive traits carried on the X tend to be more commonly expressed in males. Also because inheritance of a gamete containing a Y chromosome confers maleness, all males get their X-chromosomes from their mothers, whereas females can inherit and X chromosome from their fathers as well.
Certain types of colour blindness as well as haemophillia are sex linked.
As for Sickle cell anaemia, heamoglobin (Hb) is a tetrameric conjugated protein (2 alpha and 2 beta chains) along with iron in the Fe(II) oxidation state. When oxygen binds to Hb it binds in a cooperative manner leading to a sigmoidal binding curve, this is the result of the protein changing configuration upon binding oxygen (T to R transition). A mutation in the beta globin gene results in what should be a glutamic acid being subsitued by a valine residue realding to HbS and the consequences that we are all familiar with.
Sickle cell anaema is not sex linked, rather it is an autosomal recessive mutation. Individuals who inherit this gene often have increased resistance to malaria.
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If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!