🚀 go-pugleaf

What does allele mean ?

While I am not an expert on DNA structure I think you have entirely 
the wrong ideas about alleles and loci (plural of locus).  A locus (as 
I understand it) is a stretch of DNA that codes for example for a 
protein that is one enzyme (I think it may also be used for non-
coding regions e.g. microsatellite loci but that will just confuse 
you) - at one locus there may be different variants of the same 
locus that are called alleles.  In diploid organisms (like us humans) 
we have two copies of our DNA - so we can have at most 2 alleles 
of the same locus.  I have not heard of naming each locus by its 
position e.g. start from base 100 call it locus 100 - for exactly the 
reasons you point out this seems totally impractical as the exact 
position of a gene (or locus) varies even between individuals in the 
same population.  Alleles are variants of the same locus - they may 
have a couple of base pairs changed or maybe and extra base pair 
added (or removed) - but if they are coding for a protein like an 
enzyme then if they are too different (especially in critical places) 
they won't be able to do the "job" (and usually will be selected 
against) - one example of a critical place I assume would be the 
promoter region which turns a gene on.  

To attempt a computer analogy (which is difficult due to my limited 
knowledge) a locus is like a subroutine that does one particular task 
- alleles are different versions of a subroutine written by different 
people (actually more like badly copied versions) while these may be 
slightly different they need to do they same task and link to all the 
other parts of the program in the same way.  Of course a program that 
was anyting like DNA would be considered very poor - heaps of 
irrelevant code that does nothing - two copies of every subroutine!