Lecture 9

Question 1

What is a gene interaction?

Answer 1

-when two or more genes influence the same phenotypic trait -two genes or more interacting to determine one trait -genes interacting and dependant upon each other to produce a particular phenotype

Question 2

Give an example of gene interaction.

Answer 2

e.g.: coat colour BB;DD x bb;dd still get 9:3:3:1 ratio but only one phenotypic trait D- densely aggregated pigment d-more dilute pigment so paler colours DD dd- dense/ dilute locus controls the distribution of coloured pigment granules= it is the modifier gene

Question 3

What are the biochemical pathways in gene interaction? (coat colour Bb and coat Dd=dense/diluted)

Answer 3

Question 4

What is epistasis?

Answer 4

an allele at one gene locus masks the phenotypic expression of the alleles of another gene locus

Question 5

Does epistasis change the phenotypic ratio?

Answer 5

-alters the phenotypic ratios since we can’t get some phenotypes due to the presence of aa (in case of the agouti) then the pathway to B black is masked so even if the animal has it it won’t be expressed
aa is epistatic to B
ratio: 9:3:4 (agouti, black, albino)

Question 6

What is recessive epistasis?

Answer 6

: when have to have aa to mask the otehr gene, ratio 9:3:4

Question 7

What is dominant epistasis?

Answer 7

even just one dominant allele will lead to masking of the other gene, ratio 12:3:1

Question 8

What does it mean when phenotypic ratio adds up to 16?

Answer 8

working with two genes!

Question 9

How many blood groups are there?

Answer 9

-over 400 bllod group antigens decsribed in humans

Question 10

Which two systems of blood groups are important for blood transfusion?

Answer 10

ABO and Rhesus

Question 11

Do blood groups occur in other animals?

Answer 11

-yes (canine blood bank)

Question 12

What is an antigen?

Answer 12

antibody generator so bacteria, virus, pollen, any compound that will result in antibody generation

flu=antigen our body produces antibody

Question 13

What is an antibody?

Answer 13

= the molecule that is produced in response to the antigen

Question 14

Where are A and B antigens located?

Answer 14

• on the surface of a blood cell (they are glycoproteins= sugar with a protein attached)

Question 15

What is the dominance relationship between IA IB and IO?

Answer 15

IA and IB are codominant; IA and IB are dominant to IO

Question 16

How is the blood type determined in development by genes? (picture)

Answer 16

If have only IO than H structure stays as it is if IA then add N-acetylgalactosamine(sugar) to H and IB add galactose to H structure

Question 17

Does everyone have the H structure?

Answer 17

yes,not all H is converted

Question 18

What are the possible genotypes for blood groups A, B and O and AB? And the antigenon the surface of the cell?

Answer 18

Question 19

What antibody and antigen do all the ABO blood groups have?

Answer 19

Question 20

How do we determine a person’s blood type?

Answer 20

Take blood sample and add antisera containing known antibodies and wait to see what will agglutinate.

Type A, AB- agglutination with antiA (containing antibody A)
Type B, AB- agglutination with antiB (containing antibody B)
Type O no agglutination anti A or B (containing both antibody A and B)

Question 21

What happens when we have a matching antigen and antibody in blood?

Answer 21

Results in agglutination then death! Has to be treated within 20mins.

blood cells bound together, can’t transfer O2=death

Question 22

Which blood group is the universal donor and why?

Answer 22

Type O, becaus eit doesn’t have any antigens on the blood cells so won’t agglutinate with any other blood

Question 23

Which blood group is the niversal recipent and why?

Answer 23

Type AB, because it doesn’t have any antibodies.

Question 24

Why can antigen A and antibody B coexist in a person?

Answer 24

can co-exist together, don’t attach to each other, no match

Question 25

What is the key factor in blood transfusions?

Answer 25

- key factor is the antigen on the surface of the red blood cells(rbcs) of the donor - if the rbcs of the donor have the antigen for which the recipient has the antibody- agglutination will result - reverse doesn’t cause problems because the antibody from the donor gets diluted and it doesn’t agglutinate - parents store chord blood for later transfusions and treatment e.g. leukemia

Question 26

What blood can type A, B, AB and O get?

Answer 26

Type A can get blood from A,O Type B can get blood from B,O Type AB can get blood from A, B, O, AB Type O can get blood from O

Question 27

When does the Bombay genotype arise?

Answer 27

Have parents eg. Type A man and O mother, have B child - to get the H structure, have to have HH or Hh alleles if homozygous recessive hh then the person doesn’t develop the the antigens. So the woman had AB but was hh so didn’t get the precursor for IA or IB and tested as type O, her child got the B from her - recessive epistasis hh masks B - FUT 1 gene= bombay gene

Question 28

How common is the absence of antigen H?

Answer 28

- Bombay phenotype - 1/8000 in Taiwan - 1/10 000 in India - 1/1 000 000 in Europe

Question 29

What blood can Bombay phenotype person receive?

Answer 29

People with Bombay phenotype produce antibody H, A and B so can only receive blood from another Bombay phenotype

Question 30

How do you distinguish between Bombay and true type O?

Answer 30

-use antibody H, Type O would agglutinate because they have antigen H but Bombay wouldn’t as it doesn’t have any antigens

Question 31

Describe the MN blood system?

Answer 31

- another system of blood groups - 1 gene locus chromosome 4 - 2 alleles LM and LN –codominant - not relevant for blood transfusion as no antibodies for these in the blood plasma ## Footnote LMLM phenotype M antigen M LMLN phenotype MN antigens M and N LNLN phenotype N antigen N

Question 32

Describe the Rhesus system?

Answer 32

-blood group system -chromosome 1 -2 alleles D and d, complete dominance -3 genotypes DD,Dd,dd -2 phenotypes: Rhesus +ve (DD, Dd) approx 85% Australians =have the antigen D Rhesus –ve (dd) =allele that does nothing, no antigen D

Question 33

What are the possible issues with Rhesus in transfusions?

Answer 33

If –ve receives +ve blood = the first transfusion ok, but the incoming antigen D triggers production of the antibody and sentisizes the –ve person =second transfusion! Danger of death! -in an emergency male can get +ve blood (if it’s the first time) -never given to a female of reproductive age= pregnancy then at risk

Question 34

What is the Haemolytic disease of the newborn (erythroblastosis fetalis)?

Answer 34

-arises when Rh-ve mother (dd) carrying Rh+ve (Dd) - if parents ddxDD or ddxDd =Dd all at risk =1/2 Dd-at risk, ½ dd no risk - during pregnancy and birth fetal rbcs may enter mother’s body= antibodies produced - first pregnancy usually fine (first exposure to D antigen in the mother) - but then D antibodies from the mother cross the placenta and agglutinate rbcs of the fetus= death

Question 35

How is Haemolytic disease of the newborn prevented/treated?

Answer 35

: RhoGAM Rho(D) Immune Globin given to Rh.ve woman shortly after delivery, miscarriage or abortion. Also given to pregnant women after amniocentesis, any bleeding episodes plus seventh month of pregnancy. - injection at 28 weeks of pregnancy and after birth - the Rho(D) Immune globulin contains antibodies to the Rh D antigen-these antibodies destroy any red blood cells from the baby that have entered mother’s blood - D antibody D antigen=they do agglutinate and die but it won’t kill the mother because she will have only few of those cells in her blood= won’t affect oxygen carrying capacity!

Question 36

Can there be an issue in pregnancy with ABO groups?

Answer 36

ABO incompatibility: - blood type where the baby is either A or B or AB bood type and mother type O - blood from fetus in contact with maternal blood means antigen is in contact with antibody - less than 1% of type O mothers - the babies born jaundiced (yellowy) treated with UV light and then OK