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In <3bjm7l$ptt@woodstock.socs.uts.EDU.AU> paulk@socs.uts.EDU.AU (P J Kennedy) writes:


>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.

>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.

>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.

>So if the position isn't important why should alleles be in the same
>position on different chromosomes ? Why should they even be the same length ?
>(Indeed, are they the same length ?) Is crossover the mechanism that forces
>genes with similar effects to reside at the same locus ? ie. does crossover
>force alleles ?
Because you inherit them from your parents on that position on the
chromosome.   They are usually the same length as only insertions or
deletions will increase the length of dna associated with that allele
point mutations don't effect the length of the allele but do affect the
structure and function of the finished product i.e. the protein. 
>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.
>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 ? 

>Is it right to say that base pairs in the promoter region of a gene can
>serve as some kind of signature for that gene ? For example, if an enzyme
>wants to repress a gene for short hair and the promoter region for the
>short hair gene always contains the sequence AAATTGGGTACG then can the
>enzyme only look for this sequence rather than a much longer one that is
>the actual gene itself ?
Correct repressers which act on promoters are common e.g. lactose
operon in E.coli. 

>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 ?

Any change in a promoter will affect the amount of expression of the
gene. Promoters would be expected to be very similar in alleles although
slight variation could occur.
>Thanks in advance for anyone who can help me.


>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.