forensic science - DNA assessment

How do you calculate the frequency of specific genotype combinations of STRs given the alleles for a heterozygous genotype

2pq

Describe two different organelles within a cell where DNA can be found:

Nucleus (contains cell's DNA), mitochondria, and chloroplasts which play a role in energy conversion.

Are introns or exons more numerous in the human genome?

introns

Explain homologous pairs of chromosomes

The two chromosomes in a homologous pair are very similar to one another and have the same size and shape. They carry the same type of genetic information: that is, they have the same genes in the same locations.

Explain the purpose of the AMEL STR found on the y chromosome

The use of this gene has made the sex determination much less complicated since only one pair of primers is required to amplify the different size fragments of the AMEL genes.

Gene

a DNA segment that contributes to phenotype/function. Genes contain the code for a specific protein that functions in one or more types of cells in the body

Exon

a segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence.

Intron

a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes.

Gel electrophoresis

a technique used to separate DNA fragments according to their size.

Chromosome

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Identify the nucleotides that make up DNA

adenine (A), thymine (T), guanine (G), and cytosine (C)

describe the amount of material used in gel electrophoresis

1 agarose green gel cup used to make the wells for the DNA samples, 10 ul of each DNA sample, Diluted 135 mL TBE running buffer that let electrical charges flow through the gel

Discuss how restriction enzymes are used in DNA profiling

A restriction enzyme is a DNA-cutting enzyme that recognizes specific sites in DNA. Many restriction enzymes make staggered cuts at or near their recognition sites, producing ends with a single-stranded overhang. If two DNA molecules have matching ends, they can be joined by the enzyme DNA ligase.

Explain the complementary base pairing involved in DNA

Adenine binds to thymine and guanine binds to cytosine as they are complementary base pairs. The complementary bases can form a bond with each other. This helps to hold the two antiparallel strands of the DNA molecule together to form the helix. (A-T, G-C)

describe the purification process in extracting DNA from cells

After the separation of DNA from the aqueous solution, it is then rinsed with alcohol. Purification removes all the remaining cellular debris and unwanted material. Once the DNA is completely purified, it is usually dissolved in water again for convenient storage and handling.

Discuss how paternal inheritance can be traced using the y chromosome

Because Y-chromosomes are passed from father to son virtually unchanged, males can trace their patrilineal (male-line) ancestry by testing their Y-chromosome

Explain why DNA testing can't determine your ethnicity (race)

Biological/genetic ancestry describes variations in genetic sequences. There is no one variant that defines any racial/ethnic background

Describe RFLPs and how they are generated

DESCRIBE: Restriction fragment length polymorphisms, or RFLPs, are differences among individuals in the lengths of DNA fragments cut by enzymes. RFLP analysis can be used as a form of genetic testing to observe whether an individual carries a mutant gene for a disease that runs in his or her family. HOW THEY ARE GENERATED: In RFLP analysis, a DNA sample is digested into fragments by one or more restriction enzymes, and the resulting restriction fragments are then separated by gel electrophoresis according to their size.

Explain the melting step of polymerase chain reaction

DNA chains are heated at 95 degrees C and separated into two using primers

Explain the function of DNA

DNA contains the instructions needed for an organism to develop, survive and reproduce.

Explain how DNA is charged

DNA is negatively charged because of the presence of phosphate groups in nucleotides. The phosphate backbone of DNA is negatively charged, which is due to the presence of bonds created between the phosphorus and oxygen atoms.

Explain how various properties of DNA are used to generate the bands

DNA is negatively charged so it can be pulled through the gel by an electric field. Smaller DNA molecules move faster than larger ones, separating them out.

Briefly describe how gel electrophoresis is used to separate DNA

DNA samples are loaded into wells at one end of a gel, and an electric current is applied to pull them through the gel. DNA fragments are negatively charged, so they move towards the positive electrode.

describe the process of gel electrophoresis

DNA samples are loaded into wells at one end of a gel. They are then pulled through the gel by an electric current. Since DNA fragments are negatively charged they move towards the positive electrode.

Explain the electronic detector in STR profiling/typing

Detects glow of the STR and translates it into an electrogram.

How should you explain your evidence to a jury of your peers

Explain evidence in simple terms such as 1 out of every 10 people or 10% of people. (perform calculations to find these numbers)

Given the individual allele frequencies for different STR alleles, explain how to calculate the odds that another person could have the same DNA combinations. Do this in terms of probability and chance (ex: 1 out 60 million)

For heterozygous genotype pairs, use the formula 2pq with p and q representing the alleles. For homozygous genotype pairs, use the formula p^2 with p being the alleles at that LOCI, which should be the same. Then, after doing this for all alleles, multiply all those values together. After that, divide it by 1 to get a value similar to 1 out of 60 million or something like that.

Distinguish between an allele and a gene

Genes are a portion of DNA that determines a certain trait and are responsible for the expression of traits. Alleles are a specific form of a gene and are responsible for the variations in which a given trait can be expressed

Discuss the relationship between genes and chromosomes

Genes are contained in chromosomes, which are in the cell nucleus.

Distinguish between the terms homozygous and heterozygous STR genotypes

HOMOZYGOUS: The presence of two identical alleles at a particular gene locus. A homozygous genotype may include two normal alleles or two alleles that have the same variant. HETEROZYGOUS: The presence of two different alleles at a particular gene locus. A heterozygous genotype may include one normal allele and one mutated allele or two different mutated alleles

Describe a homozygous condition

Homozygous condition means that there are homologous pairs of chromosomes and the gene codes for the exact same phenotype

Describe how a human chimera may develop

Human chimeras are people born with different genomes. This is when multiple fertilizations happen in the womb. Two independent early embryos (are clumps of cells) fuse together and go on to develop normally as a single individual.

Discuss the relationship between DNA and chromosomes

In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure

Describe the importance of PCR to DNA profiling

It allows us to generate millions of DNA copies from a single strand of DNA

Describe how gene frequencies for different STRs are determined using population databases

It is determined by counting how many times the allele appears in the population then dividing by the total number of copies of the gene.

Explain relative fluorescence in STR profiling/typing

Measurement unit indicating the amount of fluorescence

Describe the steps for polymerase chain reaction

Melt -> Anneal -> Extend

Compare and contrast nuclear DNA with mitochondrial DNA (mtDNA) in regards to the role of each in the identification of persons

NUCLEAR: Each person's nuclear DNA is unique—except for identical twins, who have the same DNA. When a sufficient nuclear DNA profile from the victim's remains matches the nuclear DNA profile from a sample known to have come from the victim, we can be very sure of the identity of the victim. MITOCHONDRIAL: A mitochondrial DNA test (mtDNA test) traces a person's matrilineal or mother-line ancestry using the DNA in his or her mitochondria. mtDNA is passed down by the mother unchanged, to all her children, both male and female.

Compare and contrast nuclear DNA with mitochondrial DNA (mtDNA) in regards to inheritance from the parents

NUCLEAR: Nuclear DNA adheres to Mendelian inheritance, with information coming from two parents, one male, and one female. MITOCHONDIRAL: Mitochondrial DNA is inherited entirely from the mother

Compare and contrast nuclear DNA with mitochondrial DNA (mtDNA) in regards to the quantity within the cell

NUCLEAR: Nuclear DNA is located within the nucleus of eukaryote cells and usually has two copies per cell MITOCHONDRIAL: mitochondrial DNA is located in the mitochondria and contains 100-1,000 copies per cell.

Explain how the 4th amendment relates to CODIS and the collection of DNA

Once a person's DNA profile has been entered into CODIS database, "police at any level of government with a general criminal investigative interest ... can tap into that DNA without any consent, suspicion, or warrant, long after his period of supervised release ends."

Explain fluorescent tags in STR profiling/typing

Tags placed on the STR sequences that glow in the presence of light. The fluorescence shines brighter when the STR is homozygous, so it helps indicate whether it's homozygous or heterozygous.

Explain the anneal step of polymerase chain reaction

The DNA is cooled at 60 degrees C and two more primers are added, binding to the original two primers.

Explain the extend step of polymerase chain reaction

The DNA is heated at 70 degrees C and polymerase attaches to the primers and extends, creating two more copies of the DNA chain.

Describe a heterozygous condition

The heterozygous condition means that there are two different alleles.

Explain in capillary tubes STR profiling/typing

The mix of billions of short fragments from the PCR is loaded into either a shallow tray or a series of glass capillary tubes that contain a gel solution that serves as a sieving matrix. This sieve allows smaller molecules to pass through more readily than larger ones.

Do introns or exons code for a proteins?

exons

Summarize the process for extracting DNA from cells

lysis -> precipitation -> purification

Allele

one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

How do you calculate the frequency of specific genotype combinations of STRs given the alleles for a homozygous genotype

p^2

describe the precipitation process in extracting DNA from cells

separates the freed DNA from the cellular debris

describe the lysis process in extracting DNA from cells

the nucleus and the cell are broken open, thus releasing DNA