Forensic Biology: Lecture 2 – Sources of DNA, DNA Extraction and Quantification

Mendel's Law of Segregation

Expression of a trait is controlled by discrete units, which occur in pairs.

Alleles

Discrete units that control the expression of a trait.

Genotype

The combination of two alleles for a gene.

Homozygous genotype

Having two of the same allele for a gene.

Heterozygous genotype

Having a combination of alternative allele forms for a gene.

Mendel's Law of Independent Assortment

Alleles for one trait will assort independently of those for another trait.

Meiosis

The process of cell division that results in the formation of gamete cells.

Segregation

The separation of homologous chromosomes into gamete cells during meiosis.

Independent Assortment

Non-homologous chromosomes can combine in many different ways during meiosis.

Linkage

Genetic markers found close together on the same chromosome are transmitted as a block.

Recombination

Acts to reduce linkage between genes located far away on the same chromosome or different arms.

Flowchart

A visual representation of a process or system.

DNA Typing

The process of determining the genetic profile of an individual using DNA analysis.

qPCR

Quantitative Polymerase Chain Reaction, a technique used to amplify and quantify DNA.

Organic Extraction

A method of DNA extraction where DNA remains in the aqueous phase while other cellular material moves to the organic layer.

Background Sample

A control sample used to account for any background contamination or interference in DNA analysis.

Detection

The process of finding trace amounts of biological material such as blood, semen, or saliva.

Collection

The secure acquisition and transfer of evidence to the laboratory for analysis.

Degradation

Efforts to prevent further fragmentation of DNA into smaller pieces.

Contamination

The addition of new biological material to the evidence, which must be prevented.

Mixture

The combination of different DNA samples during the commission of a crime.

Biological Evidence Collection

The process of collecting biological evidence from a crime scene.

Chelex Extraction

A method of DNA extraction that uses an ion exchange resin to remove metal ions that may inhibit PCR reactions.

FTA Paper

A type of filter paper used to collect and preserve DNA samples.

Differential DNA Extraction

A method of DNA extraction used to isolate the male DNA fraction from the female DNA fraction in sexual assault cases.

Qiagen DNA Mini Kit

A kit used for DNA extraction that uses a silica-based membrane to purify DNA from various sample materials.

DNA Quantification

The process of determining the concentration or quantity of extracted DNA in a biological sample.

Yield Gels

Gels used to estimate the concentration and quality of DNA in a specimen.

UV Spectroscopy

A method of DNA quantification that measures the optical density of a DNA solution at a specific wavelength.

Slot Blot Hybridization

A method of DNA quantification that uses a probe to estimate the amount of DNA in a sample.

Real-Time PCR

A method of DNA quantification that measures the fluorescence produced during the amplification reaction.

Amelogenin

Exists in tooth enamel, used for sex determination. Gene is found both in the X and the Y chromosomes, but there is a deletion of 6 bp within intron 1 on the X-chromosome not present on the Y-chromosome.

TAQMAN method

A type of real-time PCR and uses a nucleic acid probe complementary to an internal segment of the target DNA. The probe is labeled with two fluorescent moieties. The emission spectrum of one overlaps the excitation spectrum of the other, resulting in "quenching" of the first fluorophore by the second.

Polymorphism

The coexistence of two or more distinct forms in the same population.

Sex determination using Amelogenin:

DNA profile identification amplify a number of STR polymorphisms and Amelogenin.

CODIS

Combined DNA Index System

Sanger sequencing

Dideoxynucleotides halt DNA polymerization at each base, generating sequences of various lengths that encompass the entire original sequence. Terminated fragments are electrophoresed and the original sequence can be deduced.