Re: Hypothetical gene-replacement and (lack of ?) effects on phenotype.

Hi there, 

Well, that's an interesting one. It would probably depend upon whether the 
cells which would respond to the alterations were alive or dead.  E.g. if 
the hair follicles were dead rather than dormant then a gene coding for a 
mane growth couldn't make much difference.  It could only cause hair to regrow
if the hair follicles could be re-activated or if the source of new hair 
follicles could be activated/grown. 

As for sexual maturity, if your hormones were altered then, even as an 
adult, quite dramatic changes in the body can occur over time.  Look at 
transgender individuals who have hormone therapy - they can grow/lose 
facial hair, grow breasts etc.  People who have abnormal growth hormone 
can find that their height increased or the length of the fingers and 
toes. I'm not sure how eye colour would work as if you had light eyes but 
suddenly started making a dark pigment then perhaps they would change (not 
sure).  If you had dark eyes then wanted to go light the pigment in the 
eyes would have to naturally break down before the pale colour would be 
visible.   The answer to all this is probable that it is easier to add 
things than take them away so you wouldn't be able to ungrow your height 
but if a process of loss is reversible e.g. hair loss then perhaps new 
genes would help.  All these developmental processes are very finely 
balanced though.  What if you put in a hair growth gene and the gene for 
controlling it had been switched off?  You could get hair everywhere!