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In article <3bjm7l$ptt@woodstock.socs.uts.EDU.AU> paulk@socs.uts.EDU.AU (P J Kennedy) writes:
>From: paulk@socs.uts.EDU.AU (P J Kennedy)
>Subject: What does allele mean ?
>Date: 1 Dec 1994 05:16:37 GMT


>Hi all,

>I am a computer scientist trying to understand genetics. With this
>in mind, I have the following questions.

>I understand the term locus to mean the position of a gene on a chromosome.
>For example, if a gene spans the 100th to the 175th base pairs of the
>chromosome then its locus is 100.

Well, yes. A locus is the position of a gene. It's localization is NOT, 
however as rigidly set as that - how could it be, when not even all alleles of 
a particular locus are necessarily all the same lenght. 

Think it like this: A chromosome is a desk of drawers, where each drawer is a 
locus (say, called "socks") and an allele is the exact pair of socks you find 
inside. 

>I understand the term allele to mean genes which have different effects
>on a single characteristic that are at the same loci on homologous 
>chromosomes.

See above.

>Is the actual locus of a gene on the genetic strip important ?
>From what I understand I don't think it is because a gene will either always
>be expressed (ie. it's constitutive) or it will be turned on or off by other
>genes and this is controlled by what the gene or its promoter looks
>like not its actual position on the strip.

On the contrary! It's very important! The level of expression depends on the 
situation of the gene in chromosome. The expression pattern depends on 
surrounding genes etc. 

Biological systems are not on/off systems. It is not enough to know whether a 
gene is expressed or not. You need to know when, and to what extent it is 
expressed.

>So if the position isn't important why should alleles be in the same
>position on different chromosomes ?

See above. If your socks are in your "ties" drawer, you gonna look funny when 
you dress up ;-) (Remember, you dress up by the labels on the drawers, not by 
the appearance of the contents.)

>If, by inversion, an allele of a gene is moved from one locus to another
>position, is it still an allele ? If it is, then the whole definition of
>alleles seems, to me, to be inconsistent.

No, the definition of an allele is "the different variations of a gene locus".

>Is the garbage information that now fills its old locus an allele ? If it
>isn't (as I would expect) then does that mean that at a particular locus one
>finds either alleles of a gene, garbage or other genes ? 

Well, yes. It would be an allele. Naturally, If it's total garbage and the 
gene is important, we won't have an individual. A mutant is, by definition, an 
individual with garbage in (one of) it's loci.

>Is it right to say that base pairs in the promoter region of a gene can

Not as simple as that. Most of the finesses are not yet known.

>Must each of the alleles of a particular gene have the same information
>in the promoter sequence ? By that I mean, do all alleles of a gene have to
>be turned on in the same way and have the same signature ?

They don't have to and, indeed, they don't always have. They have very SIMILAR 
sequences, sure - but that is to be expected when one thinks about 
evolutionary processes.

>Thanks in advance for anyone who can help me.

Don't mention it. 

What I can't understand, mind you, is why you come to the net with these 
questions. They can't be answered very well in such a short space. Why don't 
you instead find a good introductory text to genetics? You can read, right?
Try "The Science of Genetics" by Burns, for example. It should be 
comprehensible even with limited background in biology (high-school level 
should be enough).

>Regards,

>Paul Kennedy

>School of Computing Science,
>University of Technology, Sydney.
>--
>------------------------------------------------------------------------------
>Paul Kennedy - paulk@socs.uts.edu.au
>School of Computing Sciences, University of Technology, Sydney.
>PO Box 123 Broadway NSW 2007 Australia.


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