3 - 7 - Week 3B - 1 Blood (13 02), kryminalistyka, introduction to forensic science
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[MUSIC][MUSIC]The topic of this lecture is Blood and theforensic uses of blood evidence.This topic is sometimes called forensicserology.In a violent crime, there is likely to beblood spilled.There may be blood on the victim,there may be blood around the crime scene,and there may be blood on the suspect.If it's fresh blood, then it's fairlyobvious that it is blood, but if it's old,dried blood, it's not always possible totelljust by looking at it that it is blood.So we need to have some tests to find outifthese stains on the suspect or the crimescene actually are blood.And in some cases, for instance, if thecrime scenehas been cleaned up, there may be novisible signs of blood.So we need a test to show up these signsof blood.Once you've found blood and you'vedetermined that itis blood, then the question is, is ithuman blood?And if it is human blood, whose blood isit?Now, in a violent crime, where there's a lotof blood scattered around the crime scene,another question arises -can we use the pattern of how theblood is spattered to reconstruct theevents that occurred?So these are some of the questions we'lladdress in this lecture.Now, what is blood?It's a very, very complex substance. Itmakes up about 8%of our body weight, so there's a lot of itabout.Now blood is, as we know, a liquid.But it's only just a liquid, so the fluidportion of blood, whichis the blood plasma, is just over half ofthe blood by weight.And this consists of water and variousother biochemicalssuch as proteins, nutrients, and alsowaste products from our metabolism.So, blood acts as a transport system tomove all these substances around the body.Now, blood also contains blood cells andthis makes up the remainder of thematerial,and there are different cells for doingdifferent things.The red blood cells, their principal jobis oxygen transport.It's to transport oxygen from the lungs downto the cells where it's needed.There's also the white blood cells.These are responsible for our immuneresponse.And then there's also platelets, and theseare responsible for the clotting response.Let's look closely at the red blood cells.They're not very big.They're about 7.8 microns in diameter,so you can get about 5 million in a microlitre.They have this particular concave shape,as shown in the picture.And one of the odd things about red bloodcells that makesthem different from all our other cellsis that they contain no nucleus.That means that the red blood cells, asthey contain no nucleus, do not containDNA.So if we're getting DNA evidence from blood,then thatDNA must come from the other cells thatare present.As we've mentioned, the principal functionis transport of oxygenby binding of oxygen to the hemoglobinmolecules that are present.On the surface of the red blood cells,there are some special proteins which arecalled antigens,and it's these antigens that areresponsible for the phenomenon of bloodtyping.Now there's many, many different kinds ofthese antigens.In fact, there's well over 100, if you caninclude some of the rarer antigens aswell.But a few of the antigens are much morecommon than the others,and it's these antigens that give us theA-B-O system of blood typing.You know very well that if you have abloodtransfusion, you must be given blood ofthe right type.Now, in the very early days whenblood transfusion started and nobodyunderstood blood type,some people would get a blood transfusionand be fine, and some people wouldget a blood transfusion and they would bevery ill or they would die.And this confusion was only sorted out byKarlLandsteiner in the early part of thetwentieth century,and he won the Nobel prize for medicinefor developing the A-B-O system of bloodtyping.Now, how does blood type work?Well, if you have type A blood, it meansthat onthe surface of your red cells, you havethe A antigen.If you have type B blood, then on thesurfaceof your red blood cells, you have the Bantigen.If you're a type AB, then on the surface ofthe cellsyou have both sets of antigens, both the Aand the B.And if like me you're a type O, then on thesurfaceof the red cells, you have neither the Anor the B antigens.Now, the percentage of people who havethesedifferent blood types varies from countryto country.Here in Singapore, the O is the mostcommon, it's at about 40%,and the AB is the least common, down atabout 5%.Now, what does blood type mean?The only thing blood type means is whatkind of antigens you have on your red cellsurfaces.It doesn't mean anything else.In some countries however, it's thebelief, it's commonlythought that your blood type also dictatesyour personality.So this movie for instance here asks, isyour blood type the key to true love?Well, the answer to that is no.And here is a former minister of theJapanese government,who got into a lot of trouble and had toresignbecause of some insensitive comments thathe made,and his excuse was that he was a type B.In reality, blood type doesn't meananything like this.Now to go with the antigens, we have theantibodies.The antibodies are big protein moleculeswhichmake up a large component of our blood,and they are produced as part of ourimmune system.The purpose of an antibody is to bind toany objects in the blood that theyrecognise as alien.Okay, so anything in the blood thatshouldn'tbe there should be bound up by anantibody.So if you look at the structure of theantibody, it's Y-shaped,and you can see two hands sticking out,and that the, those hands on the end,these are the antigen binding sites.The important thing about the antibodiesis that the interactions are extremelyspecific.The antibody will only bind to its targetand not to anything else.So the blood serum can contain antibodiesthat correspondto the surface antigens of the red bloodcells.So, there's the anti-A antibodies andthe anti-B antibodies.So if you're blood type A, then yourblood will contain the anti-B antibodies,because if you're type A, then the Bantigens would be alien to your blood.If you're type B then of course, you'llcontain the anti-A antibodies, because Awould be alien.So you have the antibodies which are theopposite to your blood type.So if you are AB, where you have bothsets of antigens, then you don't haveeither kind of antibody.If you are type O, where you have neitherkind ofantigen, then your blood will contain bothsets of antibodies.A type A person will have the anti-Bantibodies in the blood.These antibodies cannot bind to theantigens on the type A red cells.Now remember that the antibody has twohands, it has two binding sites,which means that the antibodies, theanti-B antibodies, and theB red cells will clump together in thiscomplex network.This is called agglutination,and this will result in serious medicalproblems.As I mentioned before, there are manydifferent antigens, and theA-B-O typing system is based on just the Aand the B antigens.Of the less common or less often usedantigens, the one that's more studied isthe D.And this is why when you talk about yourblood type, you don'tjust say A, AB, B, O, you also addpositive or negative.So if you have a positive blood type, thenit means you have the D antigen.If you have a negative blood type, then youdo not have the D antigen.So on average, about 85% of peopleare rhesus positive and 15% are rhesusnegative.So if we recalculate the percentage ofpeoplewith the different blood groups using thisinformation,then O positive becomes the most common,and AB negative becomesthe least common, at about 1% of thepopulation here in Singapore.Now, let's think about blood type in termsof forensic science.One of the objectives of forensic scienceis totake evidence from the crime scene andindividualise it.That is, to associate it with a singleperson.And if you look at the percentages here,you can see thatblood type, or blood group, is really notvery individualised at all.When you talk about the common types, likeO positive or B positive,that's a lot of people.And even when we go to the least commonblood type, theAB negative, we are still talking about50,000 people in this country.So blood type is really not veryindividualised at all.Well, to address this problem, studies werecarried out on the less commonantigens to try and get towardsindividualisation of blood type,and a lot of work was done on studyingthese antigens.But then everything changed.In 1990 or so, DNA technology wasintroduced,and DNA technology means that you can takea blood sample and you can individualiseit.And therefore, all this research into theforensic uses ofthese minor antigens stopped, because ithad been superseded by DNA.That doesn't mean that blood type is notimportant,it just changes the way that we use bloodtype.So, blood type cannot be used to proveguiltbecause it's not individualised.Blood type can be used to establishinnocence.Suppose at the crime scene, the blood foundthereis type A and your suspect is type B.Then that suspect ceases to be a suspectand you have established his innocence.But if that suspect was type A, itdoesn't prove that he was guilty.It just means you have to go on and lookfor further evidence.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]
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[MUSIC][MUSIC]The topic of this lecture is Blood and theforensic uses of blood evidence.This topic is sometimes called forensicserology.In a violent crime, there is likely to beblood spilled.There may be blood on the victim,there may be blood around the crime scene,and there may be blood on the suspect.If it's fresh blood, then it's fairlyobvious that it is blood, but if it's old,dried blood, it's not always possible totelljust by looking at it that it is blood.So we need to have some tests to find outifthese stains on the suspect or the crimescene actually are blood.And in some cases, for instance, if thecrime scenehas been cleaned up, there may be novisible signs of blood.So we need a test to show up these signsof blood.Once you've found blood and you'vedetermined that itis blood, then the question is, is ithuman blood?And if it is human blood, whose blood isit?Now, in a violent crime, where there's a lotof blood scattered around the crime scene,another question arises -can we use the pattern of how theblood is spattered to reconstruct theevents that occurred?So these are some of the questions we'lladdress in this lecture.Now, what is blood?It's a very, very complex substance. Itmakes up about 8%of our body weight, so there's a lot of itabout.Now blood is, as we know, a liquid.But it's only just a liquid, so the fluidportion of blood, whichis the blood plasma, is just over half ofthe blood by weight.And this consists of water and variousother biochemicalssuch as proteins, nutrients, and alsowaste products from our metabolism.So, blood acts as a transport system tomove all these substances around the body.Now, blood also contains blood cells andthis makes up the remainder of thematerial,and there are different cells for doingdifferent things.The red blood cells, their principal jobis oxygen transport.It's to transport oxygen from the lungs downto the cells where it's needed.There's also the white blood cells.These are responsible for our immuneresponse.And then there's also platelets, and theseare responsible for the clotting response.Let's look closely at the red blood cells.They're not very big.They're about 7.8 microns in diameter,so you can get about 5 million in a microlitre.They have this particular concave shape,as shown in the picture.And one of the odd things about red bloodcells that makesthem different from all our other cellsis that they contain no nucleus.That means that the red blood cells, asthey contain no nucleus, do not containDNA.So if we're getting DNA evidence from blood,then thatDNA must come from the other cells thatare present.As we've mentioned, the principal functionis transport of oxygenby binding of oxygen to the hemoglobinmolecules that are present.On the surface of the red blood cells,there are some special proteins which arecalled antigens,and it's these antigens that areresponsible for the phenomenon of bloodtyping.Now there's many, many different kinds ofthese antigens.In fact, there's well over 100, if you caninclude some of the rarer antigens aswell.But a few of the antigens are much morecommon than the others,and it's these antigens that give us theA-B-O system of blood typing.You know very well that if you have abloodtransfusion, you must be given blood ofthe right type.Now, in the very early days whenblood transfusion started and nobodyunderstood blood type,some people would get a blood transfusionand be fine, and some people wouldget a blood transfusion and they would bevery ill or they would die.And this confusion was only sorted out byKarlLandsteiner in the early part of thetwentieth century,and he won the Nobel prize for medicinefor developing the A-B-O system of bloodtyping.Now, how does blood type work?Well, if you have type A blood, it meansthat onthe surface of your red cells, you havethe A antigen.If you have type B blood, then on thesurfaceof your red blood cells, you have the Bantigen.If you're a type AB, then on the surface ofthe cellsyou have both sets of antigens, both the Aand the B.And if like me you're a type O, then on thesurfaceof the red cells, you have neither the Anor the B antigens.Now, the percentage of people who havethesedifferent blood types varies from countryto country.Here in Singapore, the O is the mostcommon, it's at about 40%,and the AB is the least common, down atabout 5%.Now, what does blood type mean?The only thing blood type means is whatkind of antigens you have on your red cellsurfaces.It doesn't mean anything else.In some countries however, it's thebelief, it's commonlythought that your blood type also dictatesyour personality.So this movie for instance here asks, isyour blood type the key to true love?Well, the answer to that is no.And here is a former minister of theJapanese government,who got into a lot of trouble and had toresignbecause of some insensitive comments thathe made,and his excuse was that he was a type B.In reality, blood type doesn't meananything like this.Now to go with the antigens, we have theantibodies.The antibodies are big protein moleculeswhichmake up a large component of our blood,and they are produced as part of ourimmune system.The purpose of an antibody is to bind toany objects in the blood that theyrecognise as alien.Okay, so anything in the blood thatshouldn'tbe there should be bound up by anantibody.So if you look at the structure of theantibody, it's Y-shaped,and you can see two hands sticking out,and that the, those hands on the end,these are the antigen binding sites.The important thing about the antibodiesis that the interactions are extremelyspecific.The antibody will only bind to its targetand not to anything else.So the blood serum can contain antibodiesthat correspondto the surface antigens of the red bloodcells.So, there's the anti-A antibodies andthe anti-B antibodies.So if you're blood type A, then yourblood will contain the anti-B antibodies,because if you're type A, then the Bantigens would be alien to your blood.If you're type B then of course, you'llcontain the anti-A antibodies, because Awould be alien.So you have the antibodies which are theopposite to your blood type.So if you are AB, where you have bothsets of antigens, then you don't haveeither kind of antibody.If you are type O, where you have neitherkind ofantigen, then your blood will contain bothsets of antibodies.A type A person will have the anti-Bantibodies in the blood.These antibodies cannot bind to theantigens on the type A red cells.Now remember that the antibody has twohands, it has two binding sites,which means that the antibodies, theanti-B antibodies, and theB red cells will clump together in thiscomplex network.This is called agglutination,and this will result in serious medicalproblems.As I mentioned before, there are manydifferent antigens, and theA-B-O typing system is based on just the Aand the B antigens.Of the less common or less often usedantigens, the one that's more studied isthe D.And this is why when you talk about yourblood type, you don'tjust say A, AB, B, O, you also addpositive or negative.So if you have a positive blood type, thenit means you have the D antigen.If you have a negative blood type, then youdo not have the D antigen.So on average, about 85% of peopleare rhesus positive and 15% are rhesusnegative.So if we recalculate the percentage ofpeoplewith the different blood groups using thisinformation,then O positive becomes the most common,and AB negative becomesthe least common, at about 1% of thepopulation here in Singapore.Now, let's think about blood type in termsof forensic science.One of the objectives of forensic scienceis totake evidence from the crime scene andindividualise it.That is, to associate it with a singleperson.And if you look at the percentages here,you can see thatblood type, or blood group, is really notvery individualised at all.When you talk about the common types, likeO positive or B positive,that's a lot of people.And even when we go to the least commonblood type, theAB negative, we are still talking about50,000 people in this country.So blood type is really not veryindividualised at all.Well, to address this problem, studies werecarried out on the less commonantigens to try and get towardsindividualisation of blood type,and a lot of work was done on studyingthese antigens.But then everything changed.In 1990 or so, DNA technology wasintroduced,and DNA technology means that you can takea blood sample and you can individualiseit.And therefore, all this research into theforensic uses ofthese minor antigens stopped, because ithad been superseded by DNA.That doesn't mean that blood type is notimportant,it just changes the way that we use bloodtype.So, blood type cannot be used to proveguiltbecause it's not individualised.Blood type can be used to establishinnocence.Suppose at the crime scene, the blood foundthereis type A and your suspect is type B.Then that suspect ceases to be a suspectand you have established his innocence.But if that suspect was type A, itdoesn't prove that he was guilty.It just means you have to go on and lookfor further evidence.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]