GENETICS OF BLOOD

Question 1

what are blood group antigens?

Answer 1

carbohydrate structures present on red cell membrane glycoproteins and glycolipids.

Question 2

what is the ABO gene?

Answer 2

a gene that determines the blood group of an individual by modifying the oligosaccharides on cell surface glycoproteins.

Question 3

what antigen does blood group O have on their surfaces?

Answer 3

H antigen (basic with nothing added)

Question 4

What enzyme does the ABO gene code for in order to produce the A antigen?

Answer 4

N-acetylgalactosaminyltransferase

Question 5

What enzyme does the ABO gene code for to produce the B antigen?

Answer 5

Galactosyltransferase (forms galactose and B antigens)

Question 6

what is isoagglutinogen?

Answer 6

one of the antigens naturally occurring on the surface of red blood cells that is attacked by an isoagglutinin in blood plasma of a different group, so causing agglutination.

Question 7

why is blood group inheritance not the same as Mendelian inheritance?

Answer 7

because A and B are codominant

Question 8

if 2 people both have the same phenotype (blood group A), do they have the same genotype?

Answer 8

no because there are 3 possible alleles IA IB and I, so you could get blood group A from IA i or IA IA.

Question 9

what would happen if you gave blood group B to an individual with blood type A?

Answer 9

agglutination because blood group A contains anti-B antibodies which would bind to blood group B, clump together.

Question 10

What blood types can you give to an individual with blood type B?

Answer 10

B or O

Question 11

why is AB blood referred to as universal recipient?

Answer 11

because it can receive blood from any type due to having no antibodies in their serum. (they do have A and B antigens on their surface however)

Question 12

Why can blood groups AB only give blood to other AB groups?

Answer 12

as they contain both A and B antigens on their surface

Question 13

why is blood group O referred to as the universal donor?

Answer 13

because you can give the blood to any blood group due to no antigens on their surface

Question 14

who can blood group O receive blood from?

Answer 14

just O individuals as they have both A and B antibodies in their serum that would cause agglutination otherwise.

Question 15

what does it mean if an individual is rhesus positive? what is rhesus negative?

Answer 15

it means that the D protein is found on the surface of the red blood cells. rhesus negative means these antigens are not present.

Question 16

what’s more common, RHD+ or RHD-?

Answer 16

RHD+ (85% of the population)

Question 17

how many copies of the gene do you need to have to be RHD+?

Answer 17

you can be homozygous for RHD or hemizygous (maybe due to a deletion)

Question 18

how many blood groups do we have? what are they?

Answer 18

8; A+ A- B+ B- AB+ AB- O+ O-

Question 19

what specifically is the universal donor and recipient blood group?

Answer 19

donor- O-

recipient- AB+

Question 20

how does rhesus disease come about?

what is this effect called?

Answer 20

if a RhD- women becomes impregnated by a RhD+ man and this forms a RhD+ baby. if the mother is exposed to the foetal blood then she can make antibodies against the D proteins so if she went on to have a second child who was RhD+ then the antibodies could cross the placenta and attack the foetal blood.
sensitisation

Question 21

how can rhesus disease be prevented?

Answer 21

by being screened and having an injection of a medication called anti-D immunoglobulin which will bind and neutralise any RhD+ cells to prevent the development of maternal antibodies.

Question 22

how can we minimise transfusion reactions?

how do we do this?

Answer 22

doing cross matching checks to see if the blood is compatible
we take a blood sample and add in antiA antibody to see if we get agglutination. we try this with Anti-B and Anti-D antibodies too.

Question 23

what are haemoglobinopathies?

Answer 23

inherited blood disorder in which an individual has an abnormal form of haemoglobin (variant) or decreased production of haemoglobin (thalassaemia)

Question 24

what is sickle cell anaemia caused by?

Answer 24

a mutation in the beta globin chain where glutamic acid is replaced by valine to form HbS.

Question 25

what’s the effect of sickle cell anaemia?

Answer 25

this alters Hb affinity for oxygen so under deoxygenated conditions Hb tetramers with a mutated beta globin chain to form long polymers which cause distortion of the RBCs- this can block blood vessels

Question 26

What is thalassaemia?

Answer 26

a haemoglobinopathy. it is caused by a reduction in the quantity of the alpha or beta globin chain and so reduces the amount available to carry oxygen around our bodies.

Question 27

how many copies of the gene do you have to inherit to have thalassaemia?

Answer 27

2

Question 28

where is thalassaemia most prevalent?

Answer 28

mediterranean, South Asia, Southeast Asia and Middle Eastern origin

Question 29

where is sickle cell disease most prevalent?

Answer 29

in African or carribbean descent

Question 30

describe the heterozygous advantage that sickle cell has

Answer 30

it gives relative protection from dying from malaria whereas sickle cell anaemia gives a worse chance of surviving malaria.

Question 31

how do we manage and prevent sickle cell anaemia?

Answer 31

blood transfusions at regular intervals

genetic screening of parents or postnatal screenings of baby

Question 32

What is HbS?

Answer 32

the mutated haemoglobin gene for sickle cell anaemia

Question 33

what is HbC?

Answer 33

the mutated haemoglobin gene for sickle cell trait

Question 34

what is HbE?

Answer 34

the mutated haemoglobin gene where there is a change in the amino acid, from glutamic acid to lysine .Hemoglobin E is very common among people of Southeast Asian including Northeast Indian, East Asian descent.