Human Blood
GroupsMultiple Alleles AND
CoDominance
OK… Humans and many other primates
Recall: There are three different alleles for human blood
type (multiple alleles):
Alleles
Blood Type
IA
IB
A
i
O
B
•“A” indicates the presence of 1 type of antigen (protein that can
“activate” your immune system) and “B” represents a different
antigen on the surface of a red blood cell
•“O” has no antigen on the surface of the RBC
Allele from
Parent 1
A
Allele from Genotype of Blood types
Parent 2
offspring
of
offspring
(Phenotype)
A
AA
A
A
O
AO
A
B
B
BB
B
B
O
BO
B
A
B
AB
AB
O
O
OO
O
Antibodies
• A “foreign” antigen will trigger your immune system
to create antibodies.
• Since antibodies are proteins, they have a specific
shape & will attach onto the antigen for which they
were made.
• There are bacteria in the atmosphere that have a very
similar shape to our “A” and “B” antigens & we are
exposed to them as soon as we are born.
• Therefore, each person can have antibodies
against an antigen they didn’t inherit.
• These antibodies are floating around in our
blood with our RBC’s.
• Type A blood (has A
antigens on cell surface)
has Anti-B antibodies
– Antibodies are named for
what they attack
– Anti-B antibodies attack and
will clump up (agglutinate)
in the presence of B-antigen
• Type B blood (has B
antigens on cell surface)
has A-antibodies
• Type AB blood
doesn’t have any
antibodies
• Type O blood has
Anti-A and Anti-B
antibodies
Rh Factor
• The Rh factor genetic information is also
inherited from our parents, but it is inherited
independently of the ABO blood type alleles (a
separate gene).
•There are 2 different alleles for the Rh factor known
as Rh+ and Rh-.
•Normal dominant/recessive inheritance
•Positive (+) allele is dominant to negative (-) allele
•Rh +: you have the protein
Rh-: you don’t
Mother
Father
Child
Rh-
Rh+
Rh+
Rh-
Rh-
Rh-
The “Rh Issue”… Mom = Rh-
Baby #1 = Rh+