Blood Groups, Testing, and Inheritance

Today we looked at blood types, transfusions, and inheritance. We used simulated blood type testing to give us some information about a fictional complicated family situation, and some of us tested our own blood types.

What is in blood?

Blood carries many things round the body.  It consists of a liquid called plasma, in which various things are transported.  These include red blood cells (erythrocytes), white blood cells, and platelets (which make the blood clot).  

We had a slide showing human blood on the microscope.  The magnification was 800x, whereas the photo below shows 1,000 x.  Red blood cells were easily visible, and here and there we saw irregular-shaped cells stained a different colour, which were white blood cells.

Blood smear under 1000x magnification.

Blood types

The main blood types in the UK are A, B, AB and O.  In addition there is Rhesus factor type, which is positive (+) or negative (-).

Red blood cells carry substances on their surface called antigens. The blood types are named after the types of antigen on the red blood cells.

Antigen A and antigen B are two major blood group antigens. Blood type A has antigen A on the red blood cells, and blood type B has antigen B on the red blood cells.  Blood type O does not have either antigen A or antigen B present.  Blood type AB has both antigen A and antigen B on the red blood cells. 

An antigen is something which can trigger an immune response if the body detects it as foreign. The immune system produces antibodies which attack the antigen. Normally this wouldn't be a problem, because your body does not consider your own red blood cells to be foreign; it recognises it as part of your own body.  However, it becomes critical when someone is receiving a blood transfusion - getting it wrong can lead to severe illness or death.  The reason this can happen is because blood can also contain antibodies which attack antigens A or B.  These antibodies are naturally occurring - they do not need to be triggered by exposure to the antigen, unlike, say, antibodies to viruses.  If you are blood group A, your blood plasma can contain antibodies which attack the antigens in blood group B.  These are 'anti-B antibodies'.  Similarly, if you are blood group B, your plasma may contain anti-A antibodies.  

The other major blood group is the Rhesus factor. The Rhesus protein is either on your red blood cells, or not.  If you have it, you are Rhesus Positive, and if you don't, you are Rhesus Negative.  Normally this is just shortened to + or -, so if you are blood group O and Rhesus positive, you are said to be blood group O + .  

What happens if the wrong blood is used?

If two incompatible blood types are mixed, antibodies in the plasma from one donor attack the antigens on the surface of the red blood cells from the other.  The red blood cells clump together; this is known as agglutination. This clumping can cause problems with blood flow around the body.  In addition, the red blood cells under attack from antibodies can start to break down, and the haemoglobin they contain is toxic when not safely contained in a cell.

The safest blood to give in a transfusion is a person's own type, but if that's not available, you can always give type O- because it doesn't contain any of the A, B or Rhesus antigens which the recipient might have antibodies for.  Someone with type O- blood is known as a 'universal donor' because they can give blood to anybody.

Someone with type AB blood has both antigen A and antigen B on their own red blood cells, so their immune system doesn't produce anti-A or anti-B antibodies.  If they're AB+ too then it's even better for them - they don't produce anti-Rhesus antibodies either.  These people can receive blood from anybody - their immune systems will not attack donated cells with antigen A, antigen B or Rhesus factor.  They are known as universal recipients.

Testing for blood type

The agglutination reaction is easily visible and is used as a quick test of blood types.  A drop of blood is mixed with anti-A serum, which acts like anti-A antibodies, anti-B serum, and anti-Rhesus factor serum.  

Family Mystery

We used synthetic blood to practise identifying blood types .
Our blood samples were from:

Mary - mother of baby
Matthew - newborn baby
John 
David 

By mixing drops of blood with anti-A, anti-B and anti-Rhesus serums, we were able to establish the following:

Blood Sample	Agglutination with:			Blood group:
	Anti-A	Anti-B	Anti-Rhesus
Mary	No	No	No	O -
Matthew	No	Yes	Yes	B+
John	Yes	No	Yes	A+
David	Yes	Yes	Yes	AB+

Note that it's good practice to write down your observations - what you actually see happening - before you write down conclusions.  In the table above, our observations are whether agglutination occurred or not, for each anti-serum.  Our conclusions are what that tells us about the blood group, which is the final column. Breaking it down like this makes it easier to check your work, and for others to follow it.

In our 'complicated relationship' scenario, we wanted to find out, first, who could donate blood to Mary or baby Matthew if they needed a transfusion. Poor Mary can only receive O- blood, so neither of her friends can help her.  Baby Matthew can receive O or B blood, but his mother is too ill to donate, so he will have to depend on the generosity of strangers too.  Secondly, we want to know whether John could be baby Matthew's father. In order to work this out, we have to consider the inheritance of blood groups.

Inheritance

This section is aimed at the children working at GCSE Higher level, but the younger ones may find it interesting too. 

Blood groups are determined by your genes, and the main blood groups are a good example of how dominance works.  You inherit one gene for your ABO blood group from each parent.  Alleles are different versions of a gene, and the alleles here are A, B and O.  A is dominant to O, so if you have one A and one O gene (your genotype is AO), then your blood group will be A. 

B is also dominant to O, so someone with genes BO will have blood group B.

What this really means is that you only need one gene for the A antigen in order to produce the A antigen, and the same for the B antigen.

A and B are co-dominant or incompletely dominant over each other, so if you have one each of genes for A and B, your blood group will be AB.

Your genotype is the genes you have, and your phenotype is how you turn out.  If your phenotype is blood group A, you could have genotype AA or AO, because A will 'win' and will produce the antigen even if you have only one copy of the gene for it.  If your phenotype is blood group B, you could have genotype BB or BO; you produce antigen B even if you have only one gene for it.  But if your blood group - your phenotype - is O, then we know your genotype must be OO, because if you were carrying a gene for A or B then your red blood cells would be producing some antigen A or antigen B. 

Homozygous means you have two identical copies of a specific gene, while heterozygous means you have different copies.  Someone who has genotype AA is homozygous for blood group ABO while someone with genotype AO would be heterozygous.  Both would have blood group A, though. 

Looking at our blood groups for the members of our mystery family, we can see that the mother is O, while the baby is B.  John is A, so he cannot be the baby's father as this would not explain where baby Matthew got his gene for blood group B.  On the other hand, David is blood group AB, so he can pass on genes for either A or B.  We cannot say with this test whether David is the baby's father - only that it is possible that he is.  However, we can say that John is not the baby's father.

Testing our own blood

Some of us tested our own blood type using blood-typing cards.  These cards had a small amount of dried anti-A, anti-B and anti-Rhesus serum on them.  A drop water was applied to each test field to make a solution of the anti-A, anti-B and anti-Rhesus (also known as anti-D for complex reasons!). We washed our hands, then swabbed the side of a fingertip with an alcohol wipe.  Next, we used a single-use sterile lancet to prick our own fingers, and squeezed out a small drop of blood.   A small amount of blood was applied to each test field, and we saw visible clumping on some areas. We didn't have anybody who saw no clumping in any test field - if we had, that would mean they were blood type O-.

Reuben's test card, showing clear agglutination for anti-A and anti-D.

Reuben, Thaddeus and Angie are all A+, and Hugo is B+.

Deductions about our own families

Alison knows that she is blood group O, but Reuben and Thaddeus's dad wasn't sure of his blood group.  He thought he was group O. The boys tested themselves and found that they were both A, which means that their dad could be either blood group A, or AB. 

Angie's mum knew that she was blood group O, but Angie's dad didn't know his group.  He assumed he was O as well, because it is the most common group.  However, Angie is group A and her sister Kate found out when giving blood that she is group B.  We know Angie's dad is also the father of her sister, so that means Angie's dad can only be AB.

Antonia knows that she is O - , but her husband has never been tested.  However, her four children have tested as A+, B+, A- and B+ .  O and Rhesus negative are both recessive traits, so you need two genes for the O blood group, and two for Rhesus negative, to have this phenotype. This means that Antonia's children's father can only be AB+ group with genotype AB and Rhesus genotype +-, so carrying one allele of each.  This means he is heterozygous for the Rhesus trait (carries copies of two different genes). 

The most common blood type in the UK is O at 36%, followed by A at 30%.  Type AB is relatively rare, at only 3% for AB+ and 1% for AB- , so having families with an AB member in our group is very lucky! You can find how common each blood type is on the Give Blood site.

Artificial blood?

Artificial blood of type O- (the 'Universal Donor' type) has been developed in a laboratory in Edinburgh, and trials in humans are due to start shortly.  More about this from these links:
NHS Blood and Transplant News - Trials of artificial blood to start within two years

Medical News Today - Artificial Blood

Further Work

The Blood Typing Game - an award-winning game where you save patients by testing their blood type and choosing the best transfusions from a limited range of options.

BBC Bitesize Characteristics and Inheritance - you'll need this if you're taking IGCSE Biology.  

Here is a useful worksheet to test what you've learned about blood types and compatibility of blood donations.
Worksheet: blood type problems - another one, with plenty of short questions.

Nuffield Foundation: A Closer Look at Blood .  Taking a sample of your own blood and preparing a slide.

Blood cells - labelled photographs and explanations of the cells found in blood.

May: Antibacterial Action

We wanted to compare different substances for their antibacterial properties.  Students chose 4 similar test substances from a range including: toothpastes, mouthwashes, acne treatments, household cleaners, and foods including different honeys, onions, garlic, and chillies.

Preparation

We each made pour plates of nutritional agar, seeded with a safe bacterium. Everybody successfully made their own pour plate. This can be quite tricky - you have to keep the agar at around 37-40C so that it pours freely but does not kill the bacteria.  Pouring at higher temperatures also causes excessive condensation in the petri dish later.  We put a small amount of the microbial broth culture in the petri dish, swirled it around, then poured the agar, swirled again gently, put the lid on and left it to cool.  As soon as the agar set, we inverted the plates until we were ready to use them.

Small discs of paper were sterilised in an autoclave (aka pressure cooker!) and then soaked in a test substance. These discs were blotted lightly to stop excess liquid running off them, then using forceps we placed them on the surface of the agar plates.

The plates were left for bacteria to develop. Students took their own plates home to observe, and then to measure the diameter of the 'zone of inhibition' - the circle around each disc where bacteria could not be seen in some cases.

Once some growth had occurred, the agar went cloudy and some plates had surface colonies. We observed whether bacterial growth could be seen near each paper disc. If growth couldn't be seen near a disc, but could be seen elsewhere, then it was likely that the substance on the disc had inhibited the bacteria from growing there. If this had happened, we measured the diameter of the zone of inhibition.

This activity was based on the Nuffield Practical Science activity, 'Investigating Anti-Microbial Action'

The bacterial culture that we used was Micrococcus Luteus, which was obtained from Blades Biological.  This culture is considered safe for educational use, and is apparently considered particularly suitable for comparing mouthwashes .  Angie made several new cultures from the original one, and stored more for future use.

Alison recalling the price of the Manuka honey.

We had some surprises in our results.  Some products were very effective against our bacterial culture, but this doesn't mean that we can generalise and say that these products would be effective against all bacteria.  Ideally, we would like antibacterial products to be effective against harmful bacteria and not against anything else.  To know how useful our test bacteria are, we would need to know how similar it is to the 'target bacteria' which are likely to be causing harm in that situation.   There are potential risks involved in using antibacterial products, eg encouraging resistant organisms to develop, or triggering allergies.  Or they might just be a waste of money.  The USA's Food and Drug Administration recently advised against antibacterial handwashes, for instance.

Now, on to the photos and the results!

Some samples had been prepared earlier and kept in an incubator so we could accelerate the results.  However, for the group, we cultivated our bacteria at room temperature to avoid accidentally cultivating something else which was harmful to humans.

Petri dishes were labelled on the underside so that we would know which test substance was which later.

Each person chose their own test substances.  Those being compared in this picture include chillies, garlic, onion and chilli powder.

The test discs were carefully handled with forceps to avoid contamination.

Very Serious Scientists deliberating.

Angie managed to sneak in for a Science Selfie!

Some slide-viewing for those who had time to spare - practising microscope skills.

Results

We had some striking results:

Mouthwashes - Corsodyl was very effective.  Neal's Yard 'natural mouthwash' had no detectible effect.  Curasept was effective, but not as much as Corsodyl.

Another trial of mouthwashes, compared to 6% Hydrogen Peroxide solution.  In this one, Corsodyl was very effective, Hydrogen Peroxide was a little ffective, and Curasept and Neal's Yard were not effective.  The photo does not show the results very clearly, but there are some large colonies very close to the Neal's Yard and Curasept discs, although the overall density of bacteria in those zones is low.  I think this may have been due to poor distribution of the bacteria in the agar initially.

Comparison of things you might put on a cut or a spot: Germolene, Savlon, Tea-tree oil, and Peroxiben (spot cream).  It was hard to see what had happened here - bacteria stayed away from the whole lot!  We think that tea-tree oil might have run off the surface of the disc and into other areas.  

Face washes

When comparing face washes for spotty teenagers, Superdrug's cheap own-brand version worked better at inhibiting m.Luteus than more expensive branded products.

Chillies and chilli powder

Comparison of fresh chopped chilli, dried chilli, chilli powder (which is a mix of spices) and alcohol for a control.

The perils of cryptic labels.  Anyone remember what this was?

Household cleaning sprays

Cleaning sprays - Sainsburys' cheap spray, Domestos cleaning spray, Method 'natural' spray, and Ecover spray.

Onion, garlic and chilli

Onion, garlic anc chilli - none had any detectible effect on our bacterial culture.

Handwashes

Anti-bacterial handwashes: Method 'natural' antibacterial wash was very effective, as was Simple handwash.  Palmolive wash was less effective, and tea-tree oil appeared not to be effective.

Honeys

Honeys - expensive Manuka honey, runny honey, Sainsbury's Basics honey, and Golden Syrup for a control.  We left this to develop for a few more days.  None of the honeys appeared to have any effect against the microbe in our experiment.

Honeys and propolis

Manuka honey, cheap honey, Propolis, and alcohol hand gel for a control.  The propolis stopped anything growing on the disc itself, but did not appear to have any further inhibiting effect.  The honeys didn't appear to have any effect.

Angie removed the lid for a photo, which is not ideal as it can spread mould spores.  This was done quickly and carefully!

We kept some of the experiments running for longer.  After the initial bacterial bloom, in some cases moulds took over quite rapidly.  Interestingly, the honeys seemed to promote the growth of mould, though the propolis remained untouched.  

April Agar Antics: Culturing microbes

Our April session had two activities using agar; they will be blogged separately.  This one is about cultivating micro-organisms from our environment.

We swabbed surfaces in the our homes, and tried to cultivate microorganisms from the swabs.  

Angie made up nutrient agar using chicken stock as a food source. The recipe used was:

• 2g agar powder (standard food-grade agar)
• 2tsp sugar
• 100ml chicken stock made up to half usual concentration. Don't use stock with herbs - you don't want bits in it!

Nutrient agar sterilised in the pressure cooker.

Very tasty - if you're a microbe!

This was sterilised it in the pressure cooker for 15 minutes, and was poured into petri dishes when it had cooled to 40C - 45C.  If it was poured while too hot, too much condensation developed in the petri dish later. Lids were put on the agar plates immediately, to protect them from contamination by airborne particles.

Another batch was made using beef broth (Bovril), and each petri dish was labelled either BB (Beef broth) or CB (Chicken broth).

Taking swabs from the compost caddy

To take samples, we slightly moistened a clean cotton bud from a freshly-opened pack, and rubbed it on the surface to be tested.  We lifted the lid of the petri dish and wiped the cotton bud across the agar surface in a zig-zag motion. Lids were put back on immediately, and taped in 2 or 3 places around the edge.  Each petri dish was labelled on the back with the date and surface tested. 

Innoculating the agar plate with swab

Labelling petri dishes after innoculation

Everyone took some agar plates home in a ziplock bag with some clean cotton buds, so they could swab some surfaces in their own homes.

Disposal

We practised safe disposal technique.  Once taped shut, the petri dishes would not be opened again.  They were to be kept in the open air, at temperatures below 25C, to reduce the risk of encouraging harmful organisms to grow.  After 3-5 days, people were asked to take some photos and send them to Angie.  After that, the agar plates would be put in ziplock bags and immersed in bleach for a couple of hours at least, then put in the dustbin.  

 Results

One petri dish was kept as a control - that stayed beautifully clear, with only a tiny white spot appearing after 5 days. One left open to the air for 4 hours developed all sorts of fungal and bacterial growths. Swabs taken grew all sorts of impressive-looking nasties - interestingly, while scrapings from under 5 year-old Tommy's fingernails leaped into an early lead alongside swabs from the phone keypad, they were overtaken by swabs from the toilet flush handle. 

The control stayed clear for several days, which was good evidence that the pressure cooker sterilisation and general handling had been effective in minimising contamination.

First set of swabs taken from Angie's house before the session.

Moulds started to out-compete bacterial colonies after a few days, and we saw that some colonies of microbes got an early start and seemed to thrive, but then were overtaken and apparently killed by mould. You can see some more photos of these plates below.

Phone keypad

Swabs from two different children's hands!

Swab from stair banister.

Stair banister swab (being bleached prior to disposal)

Leo's cat's paw - back view

Leo's cat's paw - top view

Leo's cat kindly donated a paw swab, above, and below are swabs Leo took from Angie's door, and his own hand:

Lydia's heating broke down, so her home was cold for this week - which probably inhibited bacterial growth:

Lydia - tap handle

Lydia - sofa arm

Lydia - outside window surface

Angie had a splinter that was suspiciously painful, so she couldn't resist swabbing it. It grew these impressive mustard - yellow bacterial colonies which look like Staphylococcus Aureus. 

Bacteria grown from swabbing a splinter on Angie's finger .:-It looks like Staphylococcus aureus, so we treated this with caution and killed it with bleach after taking photos!

Swab from Angie's splinter, with scale.

Further Reading

 These pages may help you to understand what has grown on your plates :
ScienceBuddies - Interpreting agar plates, and  Identifying unknown bacteria, by Eric Staveney

 The exercise in culturing microbes was a classic based on the Nuffield Practical Science activity, 'Microbes all around us'. 


Extra advice on doing it at home from Robert and Barbara Bruce Thompson 's Illustrated Guide to Home Biology Experiments. The author has placed the full text of the book online, freely available, to help home scientists.

Culture methods - cultivating bacteria at home http://www.gliderspen.net/glidershanger/culture.html


Scientists create works of art using bacteria