24. Blood groups and pedigrees Flashcards
What are the two most important systems for blood typing?
ABO and Rhesus
What is an antigen?
Any molecule which induces a immune response is called na antigen
What are the antigens on RBC?
The antigen is a glycoprotein embedded in the red blood cell membrane
Where is the gene located for ABO blood group?
One gene locus on chromosome 9
What is the inheritance pattern for each of the alleles?
A and B are codominant while A,B is dominant to O
What is the Bombay phenotype?
-If you are homozygous recessive for hh then you will not express the allele at the ABO locus - dominant epistasis
How does Bombay phenotype affect blood transfusion?
People with Bombay phenotype produce antibody H, antibody A and antibody B, so they can only receive good from another Bombay phenotype
If you have type A blood what antigens and antibodies do you have?
You have antigen A present and anti-B antibody present
If If you have type B blood what antigens and antibodies do you have?
You have antigen B present and anti-A antibody present
If you have type AB blood what antigens and antibodies do you have?
You have A and B antigen present. and no antibodies
If you have type O blood what antigens and antibodies do you have?
You have no antigens but both anti A and anti B antibodies
What determines which blood can be transfused?
- Key factor is antigen on the surface of the RBC of the donor
- Incoming antibody does not impact
Which ones are the universal donors and recipient?
Type O is the universal donor and Type AB is the universal recipient
What does the secretor locus determine?
If you are a secretor (Have Se allele) then you have water soluble ABH antigens in your secretions
- One locus on chromosome 19 with 2 alleles Se/se
What is the MN system?
- One gene on chromosome 4 with 2 alleles LM and LN
- Codominance telling you what antigens on the surface of the RBC
What is the Rhesus system?
- Chromosome 1 with two alleles, D/d
- Rhesus positive if you have the D allele
What happens if you have the D allele?
Presence of the D allele results in antigen D on the surface of red blood cells
What antibodies are present in the rhesus system?
There are no naturally occurring D antibodies in the blood but anti D antibodies will be produced in response to the D antigen
What does sensitisation involve for Rhesus?
- First transfusion of Rh+ to Rh- not a problem usually
- Person produces anti-D antibodies in response to D antigen and becomes sensitised
- Next contact with Rh+ blood can be fatal
What is Haemolytic disease of the newborn? HDN
- Erythroblastosis fetalis
- During pregnancy and birth fatal rbcs may enter mother’s body and antibodies are produced
- D antibodies cross placenta and agglutinate fatal rbc
How can haemolytic disease of the newborn be treated?
- Rhogam is given to Rh- women during and after pregnancy.
- Rhogam contains antibodies to the rh D antigen. These antibodies will destroy any red blood cells from the baby that have entered the mother’s blood
What is the characteristic of recessive inheritance on a pedigree?
If the trait skips a generation
- Unaffected parents have an affected child
What is the characteristics of an x linked recessive inheritance?
- Trait can skip generations
- More males affected than females
- No father to son transmission
- Affected female has an affected father
- Affected female will have all affected sons
What is the characteristics of autosomal dominant inheritance?
- All affected individuals have at least one affected parent
- Once trait disappears from a branch it does not reappear
- Around equal numbers of each sex affected
What are the characteristics for x linked dominant?
- Male with trait must passes it on to daughters only
- Affected female can pass it on to both sons and daughters
- Affected person must have at least 1 affected parent
- If a trait disappears from a branch it does not reappear
- More affected females than males
What is genetic heterogeneity?
A phenotype can be the result of mutation in different genes
- Same phenotype but due to different genes
