chromosomes! (lesson)

Each 'normal' egg has 1 X chromosome. Each 'normal' sperm has either 1 X or Y chromosome.


If XO

• When the centromere (a fibre in the centre of the chromosome that helps to split it evenly) splits the chromosome unevenly and 'pulls' an extra X chromosome to one side, there will be 2 X chromosomes in one egg and 0 X chromosomes in the other.
• 0 X chromosome from the mum and 1 X chromosome from the dad.
• The baby will have TURNER'S SYNDROME.

If XXY

• Same scenario as 'XO'. 2 X chromosomes from the mum and 1 Y chromosome from the dad.
• The baby will have KILNELFER'S SYNDROME 
• Physically abnormal: both genitalia present!

If YO

• Same scenario as 'XO' and 'XXY'. 0 X chromosome from the mum and 1 Y chromosome from the dad.
• The baby will not survive. Humans need at least 1 X chromosome to survive!
• Miscarriage!

If XXX

• Same scenario as 'XO', 'XXY' and 'YO'. 2 X chromosomes from the mum and 1 X chromosome from the dad.
• Super female! ONLY 1 X chromosome will be expressed. 
• Physically normal
• MAY be intellectually deficient
• Infertile

If XYY

• Super male! BOTH Y chromosomes are expressed. 
• Physically normal
• MAY be more violent
• Infertile

WHY older women has a higher chance of having an 'abnormal' karyotype offspring: as she gets older, the fiber that pulls the centromere weakens & detoriates. 

*Miscarriages sometimes happen because of genetic defects mentioned.

Blood types!

(Blood type: Chromosome present from each parent)

O: OO

A: AO/AA

B: BO/BB

AB: AB

*Blood types come with Rh+ or Rh-. Interesting fact: women with Rh- cannot produce offspring with men with Rh+, as the baby will be producing antigens against the mother (which will lead to miscarriage).

blood identification!

Test 1

Test 2

Test 3

DNA identity!

RECAP!: Blood splatters can provide the 'HOW' in the crime.


DNA evidence can provide the IDENTITY (who!) of the crime.


Some examples of DNA evidence:

• Baseball bat/weapon: handle/end (sweat, skin, blood tissue)
• Eyeglasses: Nose or ear pieces/lens (sweat, skin)
• Facial tissue (cotton swab): surface area (mucus, blood, earwax, skin cells!)
• Used cigarette: cigarette butt (saliva)
• Stamp/Envelope: surface area (saliva)
• Blanket/Pillow/Sheet: surface area (sweat, hair, urine, saliva)
• Fingernail: scrapings (blood, sweat, tissue)

*Blood: RBCs cannot be used, as it has NO NUCLEUS

*Urine: Not only DNA, but also traces of drugs, steroids, etc. 

What is DNA typing?

A DNA profile is an encrypted set of numbers that is an "identifier" (like a barcode!). DNA typing uses highly variable repetitive sequences, like VNTRs (variable number tandem repeats) and STRs (short tandem repeats). These can be similar in related people, but VERY different in unrelated ones.

*Polymerase Chain Reaction: Method of amplifying a single/few copies of a piece of DNA.

DNA test results first allowed to be used as evidence in 1990.

• RISK: DNA typing risks perpetrating injustice by focusing only on physical evidence in a trial
• Why?: DNA typing only tests several areas of the DNA (the only 100% sure way is to test all 23 pairs of chromosomes)
• One in 100,000 or 1,000,000 probability of two people sharing the same results.

how different blood splatters are formed! (research)

Blood dropped in different ways have different blood splatters! General rules: Higher distance, larger drop. Faster speed, larger drop. 


(summarised from http://science.howstuffworks.com/bloodstain-pattern-analysis2.htm)


Dripping/Low-Velocity Splatters
These are also known as a low-velocity spatter, the result of dripping blood. 


Force of impact: five feet per second or less
Size of the droplets: between four and eight millimeters (0.16 to 0.31 inches). This When it occurs: often after a victim initially sustains an injury, not during the infliction of the injury itself. 


Examples:

• Victim is stabbed and then walks around bleeding: passive spatters. 
• Pools of blood around the body of a victim and transfers (impressions left by weapons, or smears and trails left by movement). 
• Some injuries (ie. bleeding sustained from a punch).

Medium-velocity Spatters
Force of impact: 5 to 100 feet per second
Size of droplets: diameter is usually no more than four millimeters. 
When it occurs: 1) Caused by a blunt object, such as a bat or an intense beating with a fist, 2) stabbing. 


Unlike with a low-density spatter, when a victim is beaten or stabbed, arteries can be damaged. If they're close to the skin, the victim bleeds faster and blood can spurt from wounds as his or her heart continues to pump. This results in a larger amount of blood and a very distinctive pattern. 


High-velocity Spatters
Force of Impact: more than 100 feet per second 
Size of droplets: look like a fine spray of tiny droplets, less than one millimeter in diameter. 


*Bullet wounds are unique because they can have both back and front spatters, or just back spatters. This depends on whether the bullet stopped after entering the victim's body or traveled through it. In most cases, the back spatter is much smaller than the front spatter because the spatter travels in the direction of the bullet.

more research on blood splatters!

Angle of Impact

How Blood Drops Elongate

The narrow end of the splatter is in the direction of the travel.

Convergence of blood splatters

This is used when the blood splatters are from different directions, from the same source. The 'lines' must be drawn from a top view, to a three-dimensional position of the source.

blood spatter!

Analysing blood stains and spatters can help forensic scientists determine how & where the crime was committed. Blood stains have different shapes and sizes. This is because of the different ways the stain is created (ie. angle of impact, direction, force of impact, etc.). They are very useful to an investigator and may be able to provide conclusively the:

• Movement and direction of persons or objects while they were shedding blood.
• Position of persons or objects during bloodshed.
• Movement of persons or objects after bloodshed.
• The mechanism or object used to create a specific pattern.
• The direction a stain was traveling when it was deposited.
• The area of origin of an impact pattern.
• The minimum number of impacts during an incident.
• The sequence of events.

All blood droplets fall as spheres, due to surface tension. When they impact on a surface, they form an elliptical or circular stain.

1. What is shape of blood splatter?
1. Splatter 1: Irregularly shaped, rounded edges. 
   Splatter 2: Mostly circular, series of smaller drops in the direction of the larger drop below. 
   Splatter 3: Circular, with ‘spiked’ edges. 
   
   
   Splatter 4: Elliptical shaped stains, with trails dripping downwards.
2. Describe any other characteristic of the splatter.
1. Splatter 1: Concentrated at the bottom, with smaller drops surrounding it.
   Splatter 2: Concentrated at the bottom left, mostly, with smaller drops surrounding it.
   Splatter 3: Larger, more ‘spread out’ (no concentrated areas). Series of small drops from the left, largest drop to the right.
   Splatter 4: Entire series of large splatters against a vertical surface. 
3. What are the factors that affect the shape of the blood splatter? Name as many as possible.
1. Direction of splatter
2. Angle of impact
3. Force of impact
4. Distance of impact (similar to force?)
5. Speed of blood dropping
4. Generate some hypotheses from the blood splatter patterns observed above.
1. The larger the impact of the splatter, the larger and less concentrated the stain. 
2. The greater the angle of impact, the more elongated the splatter (ie. Splatter 4).

Experiment 1

Aim: To investigate how the diameter of the blood stains vary with the height
Apparatus: Retort stand, dropper, metre rule, protractor, clipboard, paper, artificial blood (70ml hot water + 25 g flour + food colouring), newspaper.

Procedure:
1. Lay the floor with newspaper to

Setup of Experiment 1

prevent the blood from staining the floor.
2. Attach an A4 paper onto the clipboard and place it on the floor.
3. Place the dropper loosely between the clamp on the retort stand 10 cm above the paper as shown. DO NOT SQUEEZE YET !
4. Slowly tighten the clamp to allow only ONE drop of blood to drip onto the paper below.
5. Measure and record the diameter of the blood stain in the table below. (Is one measurement of the diameter enough?)
6. Label the blood stain as “A10”.
7. Repeat Step 4 and 5 to obtain another blood stain on another spot of the paper and label it “B10”.
8. Repeat steps 3 to step 6 by adjusting the vertical distance for 30 cm, 60 cm, 100cm, 150 cm and label them appropriately.
9. Plot a graph of average diameter of blood stain, d against vertical distance, s using "Numbers".

Height/cm	LA / mm	LB / mm	LAve / mm	WA / mm	WB / mm	WAve / mm
10	8	8	8	8	8	8
30	10	10	10	10	10	10
60	11	11	11	11	11	11
100	13	12	12.5	13	12	12.5
150	13	13	13	13	13	13

Experiment 2

Aim: Investigate how the shape of the blood stains vary with the angle of impact
Procedure:
1. Lay the floor with newspaper to prevent the blood from staining the floor.2. Attach an A4 paper onto the clipboard 

Setup of Experiment 2

place it on the floor.3. Place the dropper loosely between the clamp on the retort stand least 100 cm above the paper as shown.DO NOT SQUEEZE YET !4. Elevate the clipboard to 10° as shown.5. Slowly tighten the clamp to allow only ONE drop of blood to drip onto the paper.6. Measure and record the length, L and width, W of the blood stain in the table below.7. Label the blood stain as “P10”.8. Repeat Step 5 and 6 to obtain another blood stain on another spot of the paper and label it “Q10”9. Repeat steps 4 to step 8 by adjusting the vertical distance for 30°, 50°, 70° and label them appropriately.

Angle of elevation / °	LP / mm	LQ / mm	LAve / mm	WP / mm	WQ / mm	WAve / mm
10	12	13	12.5	13	14	13.5
30	12	12	12	15	15	15
50	10	10	10	18	18	18
70	23	24	23.5	7	6	6.5

Here are the graphs! (plotted using data collected in the tables)


Experiment 1

Experiment 2