The
Ancient Chinese had long believed
that there was a special relationship evident in
blood between paternity and offspring. While not
in the least bit scientific, the mixing of blood was a
paternal test used in many courts dynasties ago. It
was not until centuries later, when scientists offered
explanations to the relationship between blood
type and paternity, that our understanding towards
blood chemistry deepened.
ABO blood groups were first identified in 1900
by Austrian physician Karl Landsteiner. With this
identification, Landsteiner discovered that blood
types are hereditary, and could be used as a way
to test for paternity. Studies then revealed that a
single ABO gene gives rise to four variants – A, B,
AB, and O – through the co-dominant expression
of alleles. In more modern science, molecular
biology allowed scientists to identify that these
genes encode enz ymes i n what i s known as
glycosyltransferase activity. This enzyme activity
plays a role in modifying oligosaccharides on
glycoproteins sitting on the surfaces of red blood
cells. Glycoproteins are antigens, the identifier to
our immune system, as well as the markers that
differentiate one blood type from another.
G l ycop r ot e i n s a r e gua r ded by va r i ou s
antibodies, which recognise the marker that signifies
“self” and “non-self”. Foreign substances, such as
viruses and bacteria, are exterminated. Likewise,
foreign blood types are rejected by antibodies that
attack certain red blood cell antigens. For instance,
people with type A blood have A antigens on their
red blood cells and make antibodies that attack B
antigens. Thus, blood transfusion is highly regulated
and could go catastrophically wrong by causing
agglutination [1].
Aside from the four blood types, the Rh blood
group system, including the Rh factor, is also
important in blood transfusion. Named after the
rhesus monkey, the Rh factor was discovered to be
similar to the antigen of this primate. The Rh factor
refers to the most important antigen within this
group and an individual either has or does not have
this antigen on their red blood cells. This is denoted
by Rh positive and Rh negative, respectively [2].
The question of why humans have blood types
to begin with has yet to be answered. Laure Segurel
and her colleagues at the National Centre for
Scientific Research in Paris surveyed ABO genes
in primates. Their conclusions showed that the
human ABO blood group likely stemmed from
when gibbons and early hominids diverged in their
evolutionary tracks [3].
In fact, by 2014 the International Society of
Blood Transfusion had recognised 33 blood group
systems, namely the MN, Diego, Kidd, and Kell.
They are fortunately less common to us because
O+
A-
B-
AB-
O-
A antigen
$ ㉾⎆
B antigen
% ㉾⎆
A+
B+
Rh factor
5K ⛇⬷
AB+
By Thomas Lee
李浩賢
This article may be useful
as supplementary reading for
biology classes, based on the DSE syllabus.
根據生物科文憑試課程綱要，本文或可作為有用的補充讀物。
