Over simplification, like many things in life, is a compromise. Text
book discussions of ABO blood typing usually stress the Mendelian
inheritance pattern of the trait. In that sense, the text authors
are not really wrong, just keeping things simple. Many times they
neglect to mention that the ABO markers are found on many cells
besides blood cells. Reality is more complex and possibly more
interesting. That does not make the text books horribly wrong.
Part of the confusion is based on methodology:
The A and B blood types are measured using antibodies to the six
sugar glycolipids (A- and B- antigens). The precursor molecule for
the A and B antigens is a five sugar glycolipid called the
H-antigen. The H-antigen does not illicit an apparent immune
response so it is not detected using common antibody assays.
Never-the-less the H-antigen exists and there must be a genetic basis
for its' formation which for the sake of simplicity can be designated
the O-gene even though more than one gene may be involved.... I do
not know much about the regulation of oligosaccharide biosynthesis in
the golgi apparatus but the order of sugar molecules is very uniform.
Could be a nifty research area.
So you see, even in a more detailed explanation, it sometimes helps
to simplify things. ;-)
>Are you saying that all of the high school biology books are wrong ???
>In a message dated 1/15/2001 8:11:38 AM Central Standard Time,
>rhall at webmail.uvi.edu writes:
>>>>Subj: Re:The Blood Group problem!!!!
>>Date: 1/15/2001 8:11:38 AM Central Standard Time
>>From: rhall at webmail.uvi.edu (Richard L. Hall)
>>To: cengulate at aol.com (CENGULATE)
>>CC: neur-sci at hgmp.mrc.ac.uk>>>>Good Morning,
>>>>>>Wrong! Everybody has the "O-gene."
>>>>>>Genes are expressed as polypeptides or proteins. The A and B antigens
>>are NOT proteins but rather <underline>glycolipids</underline> found on
>>the membranes of most human cells. The proteins produced by "A and B
>>genes" are enzymes that catalyze the addition of specific sugars
>>(either N-acetylgalactosamine or D-galactose) to a glycolipid
>>consisting of L-fucose: D-galactose: N-acetylglucosamine: D-galactose:
>>N-acetylgalactosamine:lipid. The five sugar glycolipid is sometimes
>>called the 'H-antigen" although it is actually non-antigenic. The A or
>>B antigens are formed by the addition of either N-acetylgalactosamine
>>or D-galactose to the H-antigen.
>>>>>>The so called "O gene" produces the glycosylating enzyme (or enzymes)
>>producing the "H-antigen." There are "A-genes, B-genes, and "O genes"
>>as well as an A-antigen, a B-antigen, and a "H-antigen" and they are
>>apparently inherited in a Mendelian fashion.
>>>>>><excerpt>In human blood groups the AB blood type has a gene for type A
>>>>from one parent and a gene B inherited by the other parent, so you see
>>>>are no O genes in blood group AB therefore a baby with blood type O can
>>>>Richard L. Hall, Ph.D.
>>>>Comparative Animal Physiologist
>>>>>>University of the Virgin Islands
>>>>2 John Brewers Bay
>>>>St. Thomas, U.S.V.I. 00802
>>>>>>rhall at uvi.edu>>>>>>"Live life on the edge...the view is always better" rlh
>>>>>>----------------------- Headers --------------------------------
>>Return-Path: <rhall at webmail.uvi.edu>
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>>References: <93r436$mg0$1 at news5.jaring.my>
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>>Date: Mon, 15 Jan 2001 10:11:54 -0200
>>To: cengulate at aol.com (CENGULATE)
>>From: "Richard L. Hall" <rhall at webmail.uvi.edu>
>>Subject: Re:The Blood Group problem!!!!
>>Cc: neur-sci at hgmp.mrc.ac.uk>>Content-Type: multipart/alternative;
Richard L. Hall, Ph.D.
Comparative Animal Physiologist
University of the Virgin Islands
2 John Brewers Bay
St. Thomas, U.S.V.I. 00802
rhall at uvi.edu
"Live life on the edge...the view is always better" rlh
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