Re: A question concerning human genetics.

First of all let me say how sorry I am for the delay in answering this 
question.   I  think that the concise answer to your question is that there 
are a whole number of examples of genes that work in tandem in order to 
generate a specific phenotype and this of course makes life for 
researchers, such as myself, extremely difficult.  In my lab here at the 
Universite Louis Pasteur in Strasbourg, we are studying a gene, called the 
SMN gene, that we and others believe is the primary genetic determinant of 
the infantile form of Spinal Muscular Atrophy, a dehabilitating 
neuromuscular disorder.  The SMN gene is located on chromosome 5.  However, 
it appears that the severity of Spinal Muscular Atrophy is not only 
determined by mutations on the SMN gene but also on another gene called 
NAIP.  Thus studies have shown that both mutations in NAIP and SMN work in 
tandem to determine the severity of Spinal Muscular Atrophy and the age of 
onset.  The precise function of either of  these genes is not known.  

The second example that I would like to consider in answering this question 
involves Colorectal Cancer.   Reports have been published of four genes 
being involved.  The vast majority of these act on DNA repair.  If any one 
of these genes has a mutation, then there is of course an elevated risk of 
Colorectal Cancer.  

The third and final example that I would like to use to answer your 
question involves the disease Multiple Sclerosis(MS) .  Here the results 
are even more complex because American and French teams appear to have 
identified at least 19 potential genetic sequences that could be involved 
in determining MS susceptibility.  A British team has located a number of 
genes that might be involved in a predisposition to MS development.  These 
genes are located on chromosome 6.  Another team, this time in Canada, has 
identified genes on chromosome 5. 

Thus the take-home message is that your genetics teacher is essentially 
right.  I would just like to add that there is another element that has to 
be considered and is very often forgotten which is the environment in which 
an individual grows up in.  But that is a whole different story which I 
wont go into here.  

As far as books are concerned I throughly  recommend Rasko’s Genes in 
Medicine- a very good read on the subject of Multifactorial traits.  It’s 
concise and easy to follow.


So happy reading ! ! ! ! ! !


				Robert Deyes