DNA profiling is a quick way to compare DNA sequences of two or more different organisms.
1) Isolation of DNA
Identical twins have the exact same DNA as they come from the same egg fertilised by the same sperm. Yet, their fingerprints are not the same ---> hence fingerprints do not depend on genes, they depend of the environment.
2) Cutting, sizing and sorting. Special enzymes called restriction enzymes, or "gene extractors", are added to cut the DNA at specific restriction sites. E.g. ATCGATTGC (CUT) ATCGATTGC (CUT) repeats of the core sequence. This creates different repeats of the same DNA sequence.
They are then sorted according to size through gel electrophoresis. Placed on wells in gel (seeweed agarose), placed under electric current. DNA segments move towards the positively charged cathode at different speeds. The smaller DNA segments move farther and faster.
*to separate molecules of different sizes, chromatography is also a suitable technique
Tuesday 23 August 2011
Monday 22 August 2011
Hair and Fibre Evidence
I worked with Xinyi for this pratical:D
Eyebrow hair
The root is hairy looking, the tip is white and gradually turns brown in colour towards the end.
We could see the tiny hair follicles in the strand of hair. The surface was very rough. We also had fun playing with this hair app that could see the individual strands of other peoples' hair:D
Drawing of Xinyi's eyebrow hair (the root):
Thursday 18 August 2011
Genes
How similar are we?
The results of the traits analysis of the entire sec2 cohort is in moodle:
http://moodle.rgs.edu.sg/moodle/mod/questionnaire/report.php?instance=77&sid=97&qact=vresp
In the entire secondary two cohort, Only Lai Yan and Crisann are twins in 210, based on only 6 traits. Ms Tan said that curly hair is actually a dominant gene in almost everyone! That's why our hairs curl up, even slightly, when we tie up our hair and have flyaways.
Dominant and Recessive Genes
We learnt the basics of this in Primary school, but we touched on some more advanced stuff today.
Prior knowledge:
This refers to the relationship between two variant forms of the same alleles of a single gene.
Punnet squares - Used to predict the outcome of a particular breeding, e.g. the traits of an offspring based on the parents' genes.
Today, Ms Tan talked about how meiosis occurs:) Females will always pass on 23 chromosomes with an X chromosome, while a Male may pass on X or Y chromosomes.
We did an activity of cutting and pasting two sets of chromosomes based on banding and length.
Set A: Male down syndrome. 45 + XY
Set B: 44 + XXY. Klinefelter's syndrome. The male will have both male and female characteristics as he has an extra X chromosome
YO - Y determines the gender of the person. This baby will have a spontaneous miscarriage as no human can survive without an X chromosome:) The body will recognise the baby and immediately "reject" it.
XO - Unlike YO, this person can survive. Turner's syndrome. 1 in 2500 female births.
XXX - Super female. Quite sad actually, as these people will suffer from mental retardation, infertility and other not very nice symptoms:(
http://en.wikipedia.org/wiki/Triple_X_syndrome
YYY - Super male
Hence, to sum up, there are monosomy and trisomy chromosome conditions!
In blood, people with a negative behind their letter cannot conceive children naturally as their bodies will naturally produce antibodies against their babies:(
We did an activity of cutting and pasting two sets of chromosomes based on banding and length.
Set A: Male down syndrome. 45 + XY
Set B: 44 + XXY. Klinefelter's syndrome. The male will have both male and female characteristics as he has an extra X chromosome
YO - Y determines the gender of the person. This baby will have a spontaneous miscarriage as no human can survive without an X chromosome:) The body will recognise the baby and immediately "reject" it.
XO - Unlike YO, this person can survive. Turner's syndrome. 1 in 2500 female births.
XXX - Super female. Quite sad actually, as these people will suffer from mental retardation, infertility and other not very nice symptoms:(
http://en.wikipedia.org/wiki/Triple_X_syndrome
YYY - Super male
Hence, to sum up, there are monosomy and trisomy chromosome conditions!
In blood, people with a negative behind their letter cannot conceive children naturally as their bodies will naturally produce antibodies against their babies:(
Blood Identification Tests
Test 1: Identify which is blood using hydrogen peroxide
Samples tested positive for catalase: Samples 4,5,6
Test 2: Identify which is blood using Luminol
Samples tested positive: Samples 4,5
Test 3: Kastle-Meyer Reagent
Sample 4 turned pink whereas Sample 5 did not change colour at all. Hence, my conclusion is that Sample 4 is blood.
Questions:
1. Why is it necessary to use more than one test to determine whether the given stain is blood?
More than one types of substances can give the same positive results. For example,
2. Once you know that a stain is real blood, what else would you do as a forensic scientist?
I would isolate the DNA in the blood to find out who it belongs to. If it belongs to anyone other than the victim, I can interrogate the person to find out if he or she was involved in the murder.
Sample | Prediction and reason for prediction before test | Observation (during the test) | Result |
1 | May contain blood as it is red in colour and has a high viscosity. | No bubbles | Negative |
2 | Not blood. Orange in colour. | No bubbles | Negative |
3 | Not blood. Bright pink in colour and very low viscosity. | No bubbles | Negative |
4 | May contain blood as it looks red and fairly thick. | Bubbles observed | Positive |
5 | Not blood. Bright purple in colour. | Bubbles observed | Positive |
6 | Probably not, but may be blood. Red in colour, looks like chilli with many small particles floating around | Bubbles observed | Positive |
Samples tested positive for catalase: Samples 4,5,6
Test 2: Identify which is blood using Luminol
Sample | Observation | Result |
1 | - | - |
2 | - | - |
3 | - | - |
4 | Glowed | Positive |
5 | Glowed | Positive |
6 | Glowed | Negative |
Samples tested positive: Samples 4,5
Test 3: Kastle-Meyer Reagent
Sample 4 turned pink whereas Sample 5 did not change colour at all. Hence, my conclusion is that Sample 4 is blood.
Questions:
1. Why is it necessary to use more than one test to determine whether the given stain is blood?
More than one types of substances can give the same positive results. For example,
- Luminol chemiluminescence can also be triggered by a number of substances such as copper or copper-containing alloys, and certain bleaches; and, as a result, if a crime scene is thoroughly cleaned with a bleach solution or horseradish, residual cleaner will cause the entire crime scene to produce the typical blue glow, effectively camouflaging any organic evidence, such as blood.
- Luminol will also detect the small amounts of blood present in urine, and it can be distorted if animal blood is present in the room that is being tested.
- Luminol reacts with fecal matter, causing the same glow as if it were blood.
- Luminol's presence may prevent other tests from being performed on a piece of evidence. However, it has been shown that DNA can be successfully extracted from samples treated with luminol reagent.
Hence, it is essential to use a series of tests to confirm that the given stain is really blood and not any other substance.
2. Once you know that a stain is real blood, what else would you do as a forensic scientist?
I would isolate the DNA in the blood to find out who it belongs to. If it belongs to anyone other than the victim, I can interrogate the person to find out if he or she was involved in the murder.
Tuesday 16 August 2011
DNA
Finding out more about DeoxyriboNucleic Acid:
What is DNA?
A nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. DNA lies within individual chromosomes, in the DNA helix of DNA strands. It encodes a detailed set of plans, like a blueprint, for building different parts of a cell. A DNA molecule comes in the form of a twisted ladder called a "double helix", built with the four letter DNA alphabet: A, C, T and G. DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. A always pairs with T and C always pairs with G, the the letters are connected via a hydrogen bond.
A - Adenine
C - Cytosine
T - Thymine
G - Guanine
A combination of many of these nucleobases form genes, which tell the cell to produce protein, which is essential for the cell to perform specific functions.
Animation of DNA: click to see it move!
What is a Gene?
Genes are made up of DNA. They contain the instructions on building the proteins that enable our bodies to function. For instance, out of the 25,000 genes in our body, only very few contain the specific information to make haemoglobin, while other genes contain information for other specific functions.
What is a Chromosome?
The actual length of our DNA in a single human cell is actually 3 meters long, so in order for that to fit into a cell, the DNA is packaged into compact units called chromosomes. Starting with the double helix DNA, it is wrapped around several proteins, which are packed tightly together, forming chromosomes. Each human cell has 46 chromosomes, and the DNA is organised into 23 sets of chromosomes. You can tell a person's gender from chromosomes. Also, if a human has an extra chromosome, he or she will have down syndrome.
What is a Protein?
Every cell contains thousands of different proteins, which work together to run the cell.
1) Receptor proteins are responsible for picking up nerve signals and transferring it to the next cell. For example, if someone gets hurt in the leg, the receptor proteins will transmit the pain signal all the way to the brain.
2) Structural proteins are not round but are instead column-like, stacking together to help cells extend "branches" to hold them in place, giving them their unique shapes.
Ribosomes produce these proteins, which will travel to the part of the cell where it is needed and begin to work.
What is Heredity?
The passing on of traits from parents to offspring. Our genes encode the instructions that define our traits, which are made of DNA and reside in our chromosomes. Humans have two complete sets of 23 chromosomes. Parents each contribute one set of 23 chromosomes to their offspring, passing genes to the child. When the sperm and egg cells join during conception, they create a single, 46 chromosome cell, a zygote. Each child's set of chromosomes can contain any number of their parent's chromosomes, just that each child must receive exactly one of each chromosome.
What is a Trait?
A notable feature or quality in a person. Traits are passed on from generation to generation. Types of traits include: physical traits, behavioral traits and predisposition to a medical condition. Our genes as well as the physical environment that we are exposed to (e.g. the sun) play important roles in defining our traits. When a dominant and recessive gene are placed together, the result will always be the dominant gene. Alleles can also work together to form incomplete dominance. Traits influenced by just one gene are rare. All humans share 99.9% identical DNA!
 |
| All the tested samples! |
 |
| Before adding hydrogen peroxide: Top right, sample 1, top middle, sample 2, top left, sample 3, bottom right, sample 4 and so on. |
 |
| After adding hydrogen peroxide: Samples 4,5,6 bubbled. You can even see that Sample 5 changed colour! |
Test 2 : Identify which is blood using Luminol (Samples 4-6)
 |
| Observe Sample 4 (left): it glows! |
 |
| Sample 5 (right) changes colour as well. |
 |
| Before spraying Luminol to Samples 4,5,6. |
 |
| After spraying Luminol to Samples 4,5,6. You can see that the colour of Samples 4 and 5 are much lighter than before. The light is quite bright here, so you can't see it glow, but you can see the colour change in Samples 4 and 5. |
Test 3: Kastle Meyer reagent (Sample 4 and 5)
 |
| Before adding reagent. |
 |
| After adding reagent. Sample 4 turns pink, showing that it is blood. |
DNA Extraction:
 |
| The DNA strands are three markings below the edge of my palm:) |
Friday 12 August 2011
Presentation of Adopted blood splatters:)
Hi! In our most recent bio lesson, different groups came up to present what they thought happened in other murders (by other groups) based on the blood splatters. We discussed and came up with a few things on how to tell what happened, mainly these:
Velocity
The higher the velocity, the smaller the width of the blood splatter. For example, if the blood splatter was very long and narrow, it was likely to have been made with very fast strokes. If the stroke had been slow, the splatter would most probably have been very big and splotchy. Another way to identify the velocity is also by seeing whether the end of the blood splatter ended in increasingly separated dots of blood or continued as one solid line. If the velocity was low, the latter would be observed and vice versa.
Right handed/Left handed
This is debatable and may not be very reliable. The theory was that right handers tended to draw upward strokes from the left to right whereas left handers tended to draw upward from right to left. Hence, by observing where the blood splatter started and ended (the tail end of the slash would mean the end of the slash), a forensic scientist would be able to tell if the murderer/victim was right or left handed. However, there were a lot of different views expressed as different people, right or left handed, preferred different ways of "slashing". For instance, as a right hander, I usually draw upward left to right strokes or downward left to right strokes, but some of my other right hander friends preferred downward right to left strokes. I guess it really depends and this method of identifying the murderer is not very reliable!
Angle
As done in Experiment 2 during the blood splatter practical, we made use of the knowledge gathered to interpret the blood splatters. Most of them were correct. If a blood splatter is very symmetrical and circular, it was probably made at a 90 degree angle. If it is oval shaped, it was probably made at a steeper angle; the greater the length of the oval, the steeper the angle. This angle of blood splatter can be very essential in recreating the scene of the murder, by using the point and area of convergence method with strings from one end of the room to another. Something about surface tension was mentioned as the reason for the 90 degree angle ones to be so circular, and this is what I found out:
Liquid particles exert electromagnetic force of attraction on each other. These forces are called cohesive forces, which affect the properties of liquid extensively. On the surface of liquids, cohesive forces become stronger than particles in the inner layers of the liquid because there are no neighboring atoms above. Therefore, it exhibits stronger attractive forces upon their nearest neighbors on the surface. This is called surface tension which is the tendency of the surface of a liquid to contract to possess smallest area possible. So how does surface tension play a role in the blood spatter analysis? First, gravitational force acting on blood must exceed its surface tension before a drop of blood can fall. Otherwise, there will be no blood drop since they will behave like slime or sludge. Second, no matter how high a drop of blood falls, surface tension minimizes spattering before impacting a smooth, hard surface such as glass. In other words, a drop of blood will scatter away into many small spatters without surface tension.
So essentially what it's saying is that the reason why the blood is almost perfectly round is because the blood does not splatter as after it makes contact with the surface, the gravitational force present is no longer larger than the amount of surface tension!:)
Velocity
The higher the velocity, the smaller the width of the blood splatter. For example, if the blood splatter was very long and narrow, it was likely to have been made with very fast strokes. If the stroke had been slow, the splatter would most probably have been very big and splotchy. Another way to identify the velocity is also by seeing whether the end of the blood splatter ended in increasingly separated dots of blood or continued as one solid line. If the velocity was low, the latter would be observed and vice versa.
Right handed/Left handed
This is debatable and may not be very reliable. The theory was that right handers tended to draw upward strokes from the left to right whereas left handers tended to draw upward from right to left. Hence, by observing where the blood splatter started and ended (the tail end of the slash would mean the end of the slash), a forensic scientist would be able to tell if the murderer/victim was right or left handed. However, there were a lot of different views expressed as different people, right or left handed, preferred different ways of "slashing". For instance, as a right hander, I usually draw upward left to right strokes or downward left to right strokes, but some of my other right hander friends preferred downward right to left strokes. I guess it really depends and this method of identifying the murderer is not very reliable!
Angle
As done in Experiment 2 during the blood splatter practical, we made use of the knowledge gathered to interpret the blood splatters. Most of them were correct. If a blood splatter is very symmetrical and circular, it was probably made at a 90 degree angle. If it is oval shaped, it was probably made at a steeper angle; the greater the length of the oval, the steeper the angle. This angle of blood splatter can be very essential in recreating the scene of the murder, by using the point and area of convergence method with strings from one end of the room to another. Something about surface tension was mentioned as the reason for the 90 degree angle ones to be so circular, and this is what I found out:
Liquid particles exert electromagnetic force of attraction on each other. These forces are called cohesive forces, which affect the properties of liquid extensively. On the surface of liquids, cohesive forces become stronger than particles in the inner layers of the liquid because there are no neighboring atoms above. Therefore, it exhibits stronger attractive forces upon their nearest neighbors on the surface. This is called surface tension which is the tendency of the surface of a liquid to contract to possess smallest area possible. So how does surface tension play a role in the blood spatter analysis? First, gravitational force acting on blood must exceed its surface tension before a drop of blood can fall. Otherwise, there will be no blood drop since they will behave like slime or sludge. Second, no matter how high a drop of blood falls, surface tension minimizes spattering before impacting a smooth, hard surface such as glass. In other words, a drop of blood will scatter away into many small spatters without surface tension.
So essentially what it's saying is that the reason why the blood is almost perfectly round is because the blood does not splatter as after it makes contact with the surface, the gravitational force present is no longer larger than the amount of surface tension!:)
Wednesday 3 August 2011
Blood Splatter
http://science.howstuffworks.com/bloodstain-pattern-analysis3.htm (quite an informative site about Blood Splatter)
 Blood Splatter 1 | | |
Blood Splatter 1 |
 Blood Splatter 2 | | |
Blood Splatter 2 |
multiple drips OR someone was slammed and then dragged and bounced
one main contact point (guess)
splattered evenly outwards (referring to the tiny droplets around the main blood splatter)
 Blood Splatter 3 | | |
Blood Splatter 3 |
 Blood Splatter 4 | | |
Blood Splatter 4 |
Factors affecting shape of blood splatter:
Height of where the blood originated from to the surface of blood splatter
Angle of blood splatter
Size/depth of wound, affecting the amount of blood splattered
Type of contact with surface (e.g. physical contact - person slammed against surface, non-physical - blood was dripped)
Part 1
Experiment 1 (Height):
Set-up:
Results (flipped):
Height | Diameter of blood Stain/cm | ||
A | B | Avg | |
10 | 0.8 | 0.8 | 0.8 |
30 | 1.0 | 1.1 | 1.05 |
60 | 1.1 | 1.2 | 1.15 |
100 | 1.3 | 1.3 | 1.3 |
150 | 1.2 | 1.4 | 1.3 |
Experiment 2 (angle):
Results:
Angle of elevation / ° | LP / mm | LQ / mm | LAve / mm | WP / mm | WQ / mm | WAve / mm | i/° |
10 | 13.0 | 15.0 | 14.0 | 13.0 | 14.0 | 13.5 | 83.0 |
30 | 15.0 | 16.0 | 15.5 | 13.0 | 13.0 | 13.0 | 63.3 |
50 | 19.0 | 19.0 | 19.0 | 11.0 | 11.0 | 11.0 | 39.3 |
70 | 28.0 | 26.0 | 27.0 | 9.0 | 9.0 | 9.0 | 21.6 |
Part 2
My bench's "artwork":
(huimin, xinyi, wanying and I)
The blood is dripping downwards, so it can be deduced that the blood splatter was made on the wall and not on the floor. AnYee's group guessed that the big slash in the middle was from the top down as the top has more blood than the bottom. However, we actually did it from the bottom up! The reason why the top has so much blood is because we purposely squirted a lot more blood at the end. The small slashes along the sides of the main slash were made with high velocity as the slashes are very thin and taper towards the ends, eventually separating into slanted droplets. They were also made at an angle as the individual droplets are oval shaped (we learnt this in Experiment 2 above). The handprint was supposed to be made by the murderer as the hand seems to have bled a lot in the centre of the palm and murderers usually do not get injured:)
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