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3.4.1. Inheritance of blood groups

The inheritance of blood groups

In all languages there are expressions in which family ties are related to having the same "blood", as when we speak of consanguinity to refer to people from the same family. But what is transmitted from parents to children is not the blood, but the genes that will determine their blood types and the rest of hereditary characteristics.

Human blood can be classified into different blood groups, currently more than 30 are known, although we will see the two most important systems.

AB0 system

Red blood cells (or erythrocytes) have proteins in their membrane that function as antigens. If a person receives blood with these antigens and their red blood cells do not have them, they will recognize them as something foreign to the body and their immune system will reject them, producing specific antibodies in their plasma that will neutralize them .

The inheritance of the blood groups of  the AB0 system is one of the cases that seem to violate Mendel's laws, since it is a question of multiple allelismsince there are three different possible alleles ( IA, IB, I0) although each individual it can only have two of them, one on each chromosome of the pair in which they are located.

Of the three possible alleles, IA, IB, are codominant, while I0 is recessive. Thus, there are four different phenotypes that correspond to six different genotypes:

  • Blood group A : IAI0, IAIA
  • Blood group B: IBIB, IBI0
  • Blood group AB: IAIB
  • Blood group 0: I0I0

People in group 0 do not have any of these antigens on the membrane of their erythrocytes, so they can donate blood to people in all groups, since they will not create antibodies against them . Instead, they can only receive those of other individuals in group 0 .

Those of the group A and B can only receive blood from their own group and the group 0, and can donate to those of the AB group, since those of blood group AB not create antibodies or against A or against B .

People of group AB can receive blood from any group, but they can only donate to their own blood type.

Genotype

Phenotype

Antigens

Serum antibodies

AA, A0

A

A

Anti-B

BB, B0

B

B

Anti-A

AB

AB

A and B

None

00

0

Ninguno

Anti-A and Anti-B


Grupos sanguíneos. (s. f.). Recuperado 5 de marzo de 2016, a partir de http://salud.ccm.net/faq/12346-grupos-sanguineos

Rh system (rhesus)

The other more well-known blood group system is the Rh system, based on another antigen present on red blood cells, called the Rh factor . In this case, it is a normal Mendelian character, with dominant inheritance with only two possible alleles:

  • The R allele determines the presence of the Rh antigen, and is dominant over r.
  • The r allele that determines the absence of the Rh antigen. It is recessive against R.
Individuals in the Rh+ group have R antigens on their red blood cells and therefore do not have anti-Rh antibodies. Thus, they can receive both Rh- and Rh+ type blood. Rh- group individuals do not have R antigens, and they do have anti-Rh antibodies, so they will not be able to receive Rh+ group blood.
Rh + Rh -
Genotypes RR Rr rr
Phenotype

Rh + group

Homozygous

Rh + group

Heterozygous

Rh group -

Homozygous

       

Red blood cells With R antigens No R antigens
Plasma No Rh antibodies With Rh antibodies

Possible blood donors and recipients can be summarized in this table:

Group

You can donate blood to ...

May receive blood from ...

A+

You can donate to A + and AB +

Can receive from A ± and 0 ±

A-

You can donate to A ± and AB ±

Can receive from A- and 0-

B+

You can donate to B + and AB +

Can receive from B ± and 0 ±

B-

You can donate to B ± and AB ±

Can receive from B- and 0-

AB+

You can donate to AB +

Universal receiver

AB-

You can donate to AB ±

Can receive from A-, B-, AB- and 0-

0+

You can donate to A +, B +, AB + and 0+

You can receive from 0 ±

0-

Universal donor

You can receive from 0-