Multiple Alleles and Blood
Genetics
Mendel’s Principles – A Review

Inheritance of traits is determined by genes.

Genes are passed from parents to offspring.

Alleles can be dominant or recessive.

In sexually reproducing organisms – each
adult has two copies of each gene – one
from each parent.
Exceptions to Mendel’s Work

Some alleles are neither dominant or
recessive.

Many traits are controlled by multiple alleles
or multiple genes.
Multiple alleles
Homologous
chromosomes
 Chromosomes occur in
pairs. (homologous
mean “same”)

The different alleles of
a gene occupy the
same positions on
each chromosome
Multiple alleles
So far each gene we have discussed has
been made of two possible alleles.
Ex. B = blue b= yellow
R = red r = white
Multiple alleles



However, it is possible to have several different
allele possibilities for one gene.
Multiple alleles is when there are more than two
allele possibilities for a gene.
Coat color in rabbits is determined by a single
gene with 4 possible alleles.
In rabbits, coat color is controlled by
multiple alleles. Full color (C), white
(c), light-gray or chinchilla (cch) and
white with black points or a
Himalayan (ch). Full color is
dominant to all the other alleles.
Chinchilla is dominant to
Himalayan and white.
Multiple alleles
Multiple alleles
Cross a heterozygous Chinchilla
(cchc) with a heterozygous full
h
color with himalayan (Cc ).
cchc x Cch
Multiple alleles
ch
c
C
ch
c
Multiple alleles
ch
c
C
ch
ch
Cc
c
Multiple alleles
C
ch
ch
c
c
ch
Cc
Cc
Multiple alleles
ch
c
c
C
ch
Cc
Cc
ch
cchch
Multiple alleles
ch
c
c
C
ch
Cc
Cc
ch
cchch
c hc
Multiple alleles
Genotypic Ratios:
1
ch
Cc :
1Cc : 1
ch
h
c c:
1
h
cc
Phenotypic Ratios:
2 full color: 1 light grey: 1
Himalayan
Blood Genetics

The human ABO gene is on chromosome 9.

Everyone has two copies of chromosome 9
so you have two ABO genes.

One copy is inherited from our mother, the
other from our father.
Alleles

There are three versions (called “alleles”) of
this blood type gene: A, B, and O.

A person’s blood type is determined by
which allele he/she inherits from each
parent.
Pheno vs. Geno

The genetic makeup of an organism is
called the “genotype”.

The “phenotype” is the visible properties of
an organism.

In this case, the A, B, and O allele
combination a person has is their genotype

Their blood type is their phenotype.
Dominant vs. Recessive Genes

The “A” allele is dominant and so is the “B”
allele.

Together though, the “A” and “B” alleles
are co-dominant.

The “O” allele is recessive.
Determining the Genotype



Human blood type is controlled by three alleles :
IA, IB and i.
Alleles IA and IB are dominant over i
IA and IB are codominant
Phenotype (blood type)
Genotypes
A
B
AB
O
IA IA or IAi
IB IB or IBi
IA I B
ii
Blood Types

The alleles we discussed “code” for blood
type.

What they REALLY “code” for is a specific
enzyme.

That enzyme creates specific antigens on
your RBC.
Antigens
An antigen is a protein (encoded from the
right enzyme) that “sits” on the surface of
your RBC.
 There are 2 different blood antigens, A and
B.
 If you have the A antigen, you have type A
blood.
 If you have the B antigen, you have type B
blood.

Antibodies
Blood plasma is packed with proteins called
antibodies.
 The body produces a wide variety of
antibodies that will recognize and attack
foreign molecules.
 A person’s plasma does not contain any
antibodies that will bind to molecules that
are part of his or her own body.

ABO Blood Grouping System
Blood group A
If you belong to the blood
group A, you have A antigens
on the surface of your RBCs
and B antibodies in your
blood plasma.
Blood group B
If you belong to the blood
group B, you have B antigens
on the surface of your RBCs
and A antibodies in your
blood plasma.
Blood group AB
If you belong to the blood group
AB, you have both A and B
antigens on the surface of your
RBCs and no A or B antibodies at
all in your blood plasma.
Blood group O
If you belong to the blood group
O (null), you have neither A or
B antigens on the surface of
your RBCs but you have both A
and B antibodies in your blood
plasma.
Blood Transfusions
It is important to carefully match the donor
and recipient blood types.
 If the donor’s blood cells have antigen that
are different from those of the recipient,
antibodies in the recipient’s blood recognize
the donor blood as foreign.
 This triggers an immune response resulting
in blood clotting or agglutination.

http://duongchan.files.wordpress.com/2007/05/abobloodsystem.jpg
Blood types and transfusions
People who are Type A blood produce
antibodies to agglutinate cells which carry
Type B antigens. They recognise them as
non-self
 The opposite is true for people who are
Type B
 Neither of these people will agglutinate
blood cells which are Type O as they do
not carry any antigens for the ABO
system. Type O cells pass incognito

Donor-recipient compatibility
Recipient
Type
A
B
AB
O
A
Donor
B
AB
O
Note:
 Type O blood may be transfused into all
= Agglutination
the other types = the universal donor.
 Type AB blood can receive blood from
= Safe transfusion
all the other blood types = the universal
receivers.
Donor-recipient compatibility
•
Blood group O is called
"universal donor"
because it has no
antigens on RBC.
•
Blood group AB are
called "universal
receivers” because it
has no anti- bodies in
the plasma.
Problem 1: Multiple Alleles

Show the cross between a mother who has
type O blood and a father who has type AB
blood.
i
i
GENOTYPES:
A
A
B
I
- I i (2) I i (2)
- ratio 1:1
PHENOTYPES:
IB
- type A blood (2); type B
blood(2)
- ratio 1:1
IAi
IAi
IBi
IBi
Problem 2: Multiple Alleles
 Show
the cross between a mother who is
heterozygous for type B blood and a father who is
heterozygous for type A blood.
GENOTYPES:
-IAIB (1); IBi (1);
IAi (1); ii (1)
- ratio 1:1:1:1
PHENOTYPES:
-type AB (1); type B (1)
type A (1); type O (1)
- ratio 1:1:1:1
IA
i
IB
IAIB
IBi
i
IAi
ii
Relative Abundance of Blood Types
A
B
40-42% 10-12%
AB
O
3-5%
43-45%
Rhesus Factor

The Rhesus factor gets its
name from experiments
conducted in 1937 by
scientists Karl Landsteiner
and Alexander S. Weiner.

Involved Rabbits which
when injected with the
Rhesus monkey’s red blood
cells, produced an antigen
present in the red blood
cells of many humans
Rhesus Factor (Rh)
If a person has a positive Rh factor, this
means that their blood contains a protein
that is also found in Rhesus monkeys.
 Most people (about 85%) have a positive Rh
factor
 Rh is expressed as either positive or
negative.
 The Rh factor, like other antigens, is found
on the surface of the red blood cells.

Rhesus Factor
• Positive (+) allele is dominant to negative (-)
allele
• Rh +: you have the protein
Mother
Father
Child
Rh-
Rh+
Rh+
Rh-
Rh-
Rh-
Rh-: you don’t
Rhesus Factor
 If
a person has either
two (+) genes for Rh
or one (+) and one (-)
Rh gene, they will
test Rh(+).
A
person will be
negative only if they
have 2 (-).
Rhesus Factor
•
One of the basic difference between ABO and Rh
systems is that the Rh antibodies are not natural i.e.
they are not present at birth but are synthesised in
Rh negative persons in response to the presence of
Rh-antigen.
•
Rh antigens are transmembrane proteins with loops
exposed at the surface of red blood cells.
•
They appear to be used for the transport of carbon
dioxide and/or ammonia across the plasma
membrane.
Rh Blood Group and Rh
Incompatibility
A person with Rh- blood does not have Rh
antibodies naturally in the blood plasma
Blood
Type
Alleles
Genotype
Produced
RR
R
Rr
R or r
rr
r
Rh positive
Rh negative
• A person with Rh- blood develop Rh
antibodies in the blood plasma if he or she
receives blood from a person with Rh+
blood. If such a person is given Rh+ blood,
its anti-Rh antibodies react with the donor’s
Rh antigens and aggulate the blood.
• A person with Rh+ blood can receive blood
from a person with Rh- blood without any
problems.
Why is an Rh incompatibility so dangerous
when ABO incompatibility is not during
pregnancy?
Incompatibility is seen between Rh- woman and her
foetus. Rh- woman when married to Rh+ man bears
Rh+ foetus. Although the foetal and maternal blood do
not come in direct contact due to placental barrier,
some foetal R.B.C’s manage to enter the maternal
blood stream. The Rh antigen on their surface induces
formation of anti-Rh antibodies. These antibodies then
cross the placenta and enter the foetus blood
circulation and cause a blood disorder known as
erythroblastosis foetalis. The reaction of Rh-woman
against her Rh+offspring becomes progressively more
severe with each subsequent pregnancy.
The “Rh Issue”… Mom = Rh-
Baby #1 = Rh+
Relevance of Rh Factor & ABO Typing?

It is very important in terms of babies

Example: An Rh(-) mother has a Rh (+) baby, she
will make antibody against the Rh(+) fetus
Rh Blood Group and Rh
Incompatibility
P1 : Female Rh-
×
Male Rh+
• Baby is Rh+ because father is. Mother’s
blood produces antibodies upon birth, (since
blood mixes at birth). First baby is okay.
• Second pregnancy- mom’s antibodies can
now move across the placenta and cause
baby’s RBC’s to clump (agglutinate) if second
baby is also Rh+. This decreases oxygen
delivery in the baby – “blue baby.”
What can be done?
• Mom can be given an injection of a drug
that inhibits antibody production
immediately after delivery.
What happens if this is undetected?
• Baby could be given a blood transfusion
while in the womb. Fairly uncommon.
Blood Types & Rhesus Factor Question
R – dominant allele (Rh+)
r – recessive allele (Rh-)
Example: A woman homozygous for blood
type A and heterozygous for the rhesus allele,
Rh+, has a child with a man with type O blood
who is Rh-. What is the probability that their
child will have blood type A, Rh+?
There will be a 50% chance.
Stats
O+
OA+
AB+
BAB+
AB-
1 in 3 persons
1 in 15 persons
1 in 3 persons
1 in 16 persons
1 in 12 persons
1 in 67 persons
1 in 29 persons
1 in 167 persons