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.