Phase of the Gene?

Mike Miller mbmiller at SIRRONALD.WUSTL.EDU
Fri Apr 5 11:20:04 EST 1996

On 5 Apr 1996, hua wrote:

> Please help!!!      Does anyone know what "phase of the gene" means with 
> regard to genetic linkage?   

Reference:  Ott, J. (1991). Analysis of human genetic linkage, Revised 
            edition. Baltimore: Johns Hopkins U Press.

It isn't really called "phase of the gene", but look in the index under 

Basic idea is as follows.  Suppose you have data at two genetic loci 
(Locus1 and Locus2) from one individual, as follows:

            Locus1       Locus2
            ======       ======
Alleles:      A,a          B,b

This is a double heterozygote.  But we don't know how the alleles are 
distributed on their chromosomes.  There are two possibilities, or 'phases':

            Chrom1       Chrom2
            ======       ======
Alleles:      A,B          a,b     (coupling, or trans)
Alleles:      A,b          a,B     (repulsion, or cis)

Both the coupling phase and the repulsion phase will give the double
heterozygote genotype, so we can't tell which is correct.  One chromosome
is inherited from each parent, but we can't tell what the parental
contributions were, unless we have more information. 

That's a quick overview.


Michael B. Miller, M.S., Ph.D.
Department of Psychiatry (Box 8134)
Washington University School of Medicine
4940 Children's Place,  St. Louis, MO 63110
office phone: (314) 362-9428    FAX: (314) 362-9420
WWW Homepage:

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