🚀 go-pugleaf

P J Kennedy (paulk@socs.uts.EDU.AU) wrote: 

: Hi all,

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

 I find it interesting that this sort of quesiton is being posted by a
computer scientist.  As genome database are constructed it is important
that we share a common vocbaulary so these databases have some sort of
continuity.  The following are definitions that I submit are fairly accurate
and hopefully useful in a broad context.

Locus
 The locus is the specific location of any given sequence of DNA.  This can be
a sequence of known or unknown function that is inherited according to Mendel's
first and second laws.  All of the molecular maps that exist primarily consist
of loci of unknown function.  This is because they are defined by RFLP, RAPD or
microsatellite techniques.  If a specific probe/enzyme combination gives a 
4kb fragment in parent 1 and a 2kb fragment in parent 2, then locus would consit
of two alleles represented by the 4kb and 2kb fragments.  Now if this probe is used
with another genotype (another mapping parent) and a 3kb fragment is recognized, then
a third allele would be defined.  But any one individual would only have
two of the alleles.

Gene
 A locus of known function.  This function could be defined phenotypically such
as the height locus in pea, or molecularly after the gene has been cloned.
Alleles of the genes would be the alternate phenotyic or molecular forms the
gene takes.  The alleles for plant height in pea are tall and short.  The alternate
alleles for a molecularly defined by changes in the DNA sequence via mutation or
deletion or insertion events.  The beta-globin gene change has undergone a 
single A to T mutation to generate the sickle cell anemia phenotype.  The molecuar 
probe for a gene can also be useful to assign the location of the gene on the 
molecular map.  For example, DdeI digestion and probing with the beta-globin region 
will generate bands of 201bp and 175 bp for the normal individual  and a 
single 376bp band for the individual inflicted with Sickle Cell Anemia.  This 
demonstrates how the molecularinformation can be used to place genes on the 
molecular map.

Phil McClean
mcclean@plains.nodak.edu