DNA Extraction

DNA Extraction:

Scientists isolate DNA for:

1. Genetic testing

2. Body identification

3. Analysis of forensic evidence

DNA extraction is important because the DNA first needs to be purified away from proteins and other contaminants.

Steps:

1. Collect cells from test subject

2. Burst cells open to release DNA

3. Separate DNA from proteins and debris

4. Isolate concentrated DNA

2. Burst cells open to release DNA

Lysis solution:

Contains -

Detergent

The detergent disrupts the cell membrane and nuclear envelope, causing the cells to burst open and release their DNA.

Enzyme called proteinase K

The DNA is still wrapped very tightly around proteins called histones, and the proteinase K cuts apart the histones to free the DNA.

3. Separate DNA from proteins and debris

Salt solution:

Salt causes proteins and cellular debris to clump together.

Centrifuge:

- When placing the tube containing the DNA into the centrifuge, a tube containing water is placed opposite the tube in order to ‘balance’ it.

- Inside the centrifuge, the tubes are spun around at high speed, which causes the heavy clumps of protein and debris to sink to the bottom, while the strands of DNA remain distributed throughout the liquid. The DNA can then be separated from the proteins and debris.

4. Isolate concentrated DNA

Isopropyl alcohol/ethanol:

DNA is not soluble in isopropyl alcohol and so it comes out of the solution. When put into the centrifuge again, the DNA settles at the bottom of the tube instead.

Notes taken from http://learn.genetics.utah.edu/content/labs/extraction/ when completing the DNA Extraction Virtual Lab Activity :)

Basics of DNA, Genes, Chromosomes, Heredity and Traits

DNA:

Instructions providing all the information necessary for a living organism to grow and function reside in the nucleus of every cell. The instructions come in a form called DNA. DNA encodes a detailed set of plans, like a blueprint, for building different parts of the cell.

The DNA molecule comes in the form of a “double helix”, built with the four-letter DNA alphabet: A, C, T, and G. A always pairs with T, and C always pairs with G.

G = Guanine

A = Adenine

T = Thymine

C = Cytosine

The DNA strand is made of letter, which form words, which then form sentences. These “sentences” are called genes.

Genes:

Genes are made of DNA. One strand of our DNA contains many genes. Genes are the directions for building all the proteins that make our bodies function. All these genes are needed to give instructions for how to make and operate all parts of our bodies. Proteins enable a cell to perform specific functions, such as working with other groups of cells to make hearing possible.

Chromosomes:

Each cell in our body contains a lot of DNA, thus chromosomes are used to compact DNA so that it can fit into a cell.

Packaging of DNA into a chromosome:

1. Double helix of DNA

2. DNA is wrapped around proteins

3. Proteins are packed tightly together until they form a chromosome

Heredity:

The passing of traits from parents to child is the basis of heredity.

How do we get traits from our parents?

Humans have two complete sets of 23 chromosomes (2 x 23 = 46 total)

Each child receives half of its chromosomes from the mother and half from the father.

When parents conceive a child, they each contribute one complete set to the child. This one set can contain chromosomes from both of the parent’s two sets.

Since the parents contribute chromosomes randomly to each new child, every child inherits a unique set of chromosomes and thus has a unique combination of traits.

Traits:

A trait is a notable feature or quality in a person. Each of us has a different combination of traits that makes us unique.

Physical trait:

Characteristics of one’s physical makeup e.g. eye colour, hair colour, height etc.

Behavioural traits:

Characteristics of the way one acts e.g. sheepdog’s herding instinct, a retriever’s desire to fetch etc.

Predisposition to a medical condition:

An increased risk of getting a certain type of disease is also a type of trait that can be passed from parent to child. E.g. sickle cell anemia, cystic fibrosis, heart disease, cancer, certain mental illnesses etc.

Genes encode the instructions that define our traits. The environment we live in also helps to define our traits. For example, while a person’s genes may specify a certain hair colour, exposure to chemicals or sunlight can change that colour.

Set of genetic information for each form - Allele

E.g. Straight thumb allele - “H” (dominant)

Hitchhiker’s thumb allele - “h” (recessive)

Each of us has two alleles for the thumb extension trait. We all have one of 3 possible combinations:

H + H = H

h + h = h

H + h = H --> The dominant gene will be exhibited as the trait

Two of the same allele for a trait - homozygous

Two different alleles for a trait - heterozygous

How are traits inherited?

Mother and father each have two alleles for the thumb extension trait. When they have a child, they pass one of their alleles to their child. The child’s trait is determined by the alleles he/she receives from his/her parents. Each child from these parents can receive a different combination of alleles.

Are all traits inherited this simply?

No. The thumb-extension trait is a well-defined physical trait, however most traits are more complex and thus cannot be tracked through generations this easily.

Alleles can work together to produce incomplete dominance e.g. crossing a red carnation and a white carnation can produce a pink one.

Single-gene traits:

Traits influenced by just one gene. They are rare.

Complex traits:

Traits shaped by more than one gene, sometimes many.

Notes taken from http://learn.genetics.utah.edu/content/begin/tour/ while completing the tour :

Blood Splatter Experiments

Experiment 1:

Experiment 2:

Look out for pictures of the experimental setup and the blood splatters, as well as part 2 soon! :)

Blood Splatter

These were discussed and generated by my partner, Cheryl and I so we both have similar answers:

Blood splatter 1: The shape of the blood splatter is one large drop of blood with small drops surrounding it. This

is probably created by drops of blood dropping onto a same spot. This means that the surrounding drops of blood are the result of blood dropping onto other drops of blood already on the surface and thus the impact resulting in small drops of blood being scattered around.

Blood splatter 2: This blood splatter consists of 2 main areas which contain larger amounts of blood and small droplets of blood surrounding them. As the drops of blood are not complete, they look like they may have been smudged, such as by another object coming into contact with the splatter. May have been created through a gunshot?

Blood splatter 3: The shape of the blood splatter is long and slants slightly upwards from left to right, and is more narrow on the left side than the right side. This means that the direction of the blood was north east. This splatter is most likely created by blood being flung off a swinging item that was bloody.

Blood splatter 4: The blood splatter covers a large area and consists of many smaller oval shaped splatters which have drops of blood dripping downwards. The splatter looks like it was created intentionally due to the relatively regular pattern of the blood splatter. It could have been created using a product such as red paint.

Blood Splatter Pattern from a Laboratory Experiment:

What is the shape of the blood splatters?

Circles and ovals, of varying lengths and widths.

Describe any other characteristics of the splatter.

- Jagged edges

- 2 distinct areas(inner and outer) the inner portion being a darker colour than the outer portion

- blood dropped vertically creates a blood splatter in the shape of a circle while blood dropped an an angle creates one that is in the shape of an oval, with increase in angle causing increase in the length and decrease in diameter of the blood splatter.

What are the factors that affect the shape of the blood splatter? Name as many as possible.

- angle at which the blood drop reaches the place of contact

- the distance blood is dropped at from the point of contact

- the surface of point of contact

- amount of blood that is dropped

- force used to create blood splatter(high impact/low impact)

- viscosity of blood used

Generate some hypotheses from the blood splatter patterns observed above.

1) The greater the height from which the blood is dropped, the larger the size of the blood splatter

2) The greater the angle of the plane used, the greater the length of the blood drop and the smaller the width of the blood drop

3) When a droplet of blood strikes a horizontal surface at 90 degrees it produces a circular stain. While droplets of blood that strike the surface at an angle produce a oval shaped stain

2. If dropped from the same height from the plane, the length of the blood drops will increase and the width of the blood drops will decrease as the angle of the plane on which the blood is dropped increases.

Chromatography

Below is the table of results for my pair's (Cheryl and I) chromatography:

Trace Elements - Flame Test!

OBSERVATIONS

Below are my group's observations of the colours of the flame when different elements were used:

Barium - Yellow

Calcium - Red-Orange

Copper - Green

Lead - White-Pink

Potassium - Pinkish-Orange

Sodium - Orange-Yellow

And here are the answers provided by Ms Tan as to what the colours should be:

Barium - Pale/Yellow-Green

Calcium - Orange-Red

Copper - Blue-Green

Lead - White/Blue

Potassium - Lilac to Red

Sodium - Intense Yellow

Magnesium - Bright White

Possible reasons for the differences could be due to:

- The contamination of the bunsen burner, where other elements could have dropped into the bunsen burner, causing the flame colour to change

- My group's perception of the colour of the flame could have been different

QUESTIONS and ANSWERS

1. How and what is it (flame test) used for in "crime scene investigations/forensic science"?

They are used to identify different elements found in a sample collected at a crime scene. Since the sizes of the possible jumps in energy terms vary from one metal ion to another when heated, different ions will have a different pattern of spectral lines, and so different flame colours. These different flame colours are used to identify elements. The flame colours of the elements in the sample collected at the crime scene can then be compared to the known colours of different elements, thus identifying the elements found in the sample and narrowing the search for the culprit.

2. If there are more than one trace metal present, is the flame test still a suitable technique to identify the trace metals?

No. There would be a mix of colours, making it difficult to identify the different elements. We would be unable to tell if the colour was produced as a combination of colours produced by different elements (e.g. Sodium that is yellow combined with Lead that can be white or blue may produce a green flame)

3. Is a flame test sufficient to identify the trace metal(s) present?

Although it may help to narrow down the spectrum of elements involved, it is not sufficient to identify the trace metals present solely based on a flame test. This is because some elements produce highly similar colours and others do not change the colour of the flame. Furthermore, the colour of the flame produced by the trace element is subject to our perception, making it very relative and not completely accurate.

4. What is a "Mass Spectrometer"?

The mass spectrometer is an instrument which can measure the masses and relative concentrations of atoms and molecules. It makes use of the basic magnetic force on a moving charged particle.

In order to measure the characteristics of individual molecules, a mass spectrometer converts them to ions so that they can be moved about and manipulated by external electric and magnetic fields. The three essential functions of a mass spectrometer, and the associated components, are:

1. A small sample is ionized, usually to cations by loss of an electron. The Ion Source
2. The ions are sorted and separated according to their mass and charge. The Mass Analyzer
3. The separated ions are then measured, and the results displayed on a chart. The Detector

This website is very useful for understanding the basic principle behind the mass spectrometer as well as how it works: http://www.chemguide.co.uk/analysis/masspec/howitworks.html

Fingerprinting

Answers to questions:

Ridges and Pores Activity:

Q. Where are the pores found? Are they regularly spaced?

A. They are found on the ridges of our fingers. Yes, they are, but may sometimes be erratically or randomly positioned.

Q. Are the lines of your print equally spaced throughout?

A. Mostly, but there are places where the lines merge, changing the distance between the lines. At other places the lines may not be curved in the same way as the rest, bending a different direction and thus causing the distance between the lines to change.

Cyanocrylate (Superglue) Fuming Method:

Q. If the contrast of the white print against the background is still too faint for a good photograph to be captured, what could be done to enhance the fingerprint?

A.

1. A greater amount or greater concentration of superglue could be used

2. The finger used to create the print could be made more oily first to enable a more distinct and clear print to be made

Iodine Fuming Method:

Q. What are the possible substances that may be used to render the prints more permanent?

A. The material used for printing the fingerprint on probably affects the time the print stays on it. To make the prints more permanent, they can be treated with a starch solution. Iodine and starch combine to form a deep blue-black complex, which persists for weeks to months, depending on storage conditions. Benzoflavone can also be used to treat prints to render them permanent.

Q. Why does the print disappear?

A. The natural body fats and oils in the latent print only temporarily absorb the iodine vapours when placed in the environmet containing the vapours (i.e. the gas jar), once removed from that particular environment, the vapours eventually dissipate back into the atmosphere and thus fade.

Powder Dusting Method:

Q. What is magnetic powder dusting and how does it work?

A. A magnetic applicator is used to attract magnetic powder, which is then lightly dusted over the fingerprint. It is usually used on non-magnetic, shiny surfaces such as plastic containers.

My own Fingerprint Database: Observations

1. Compare the fingerprint patterns on your right and left hand. Are they mirror images of each other?

My right and left thumbs can be considered mirror images of each other. However, the other fingers are definitely not mirror images of each other.

2. What kind of patterns do you see?

There are loops and whorls, but no arches.

3. Do the loops curve in the same or different directions in different fingers?

They are different for different fingers because no two prints are the same. One interesting thing observed is that most prints made by the left hand curve to the left and those on the right curve to the right.

4. Compare the size of the patterns e.g. How many ridges make up a loop?

Some fingers have more ridges making up the loop while others have fewer and thus smaller loops. They are not the same.