human blood groups- multiple alleles and codominance

Human Blood Groups-

Multiple 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 A

IB B

i O

•“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

Allele from Parent 2

Genotype ofoffspring

Blood types of

offspring (Phenotype)

A 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).

Mother Father Child

Rh- Rh+ Rh+

Rh- Rh- Rh-

•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

The “Rh Issue”… Mom = Rh- Baby #1 = Rh+