Untitled

Definition: DNA profiles, originally referred to as DNA fingerprints, utilize variations, or polymorphisms termed "many forms," which consist of repeated sequences of DNA.

Polymorphic Locus: A specific location on a chromosome where variations occur, leading to different alleles.
- Definition of Alleles: Historically defined as different versions of a gene. This definition has since been expanded to include varied structures or sequences of DNA.

Short Tandem Repeats (STRs): The current method for DNA profiling involves the analysis of STRs, which consist of repeated units of two to eight nucleotides.
- Location: STRs are found in noncoding regions of chromosomes.
- Example of STR Alleles:
- STR with 6 repeats: GATA GATA
- STR with 11 repeats: نيت
- Polymorphism: STRs are highly polymorphic, capable of displaying nine or more different alleles that can be detected.

Genotype Occurrence: At a given locus, if a woman inherits alleles with the same number of repeats from each parent, her genotype can be described as 16/16, indicating homozygosity at that locus.
Siblings' Inheritance: Statistically, half of the children can inherit a 3/16 genotype, while the other half can get a 10/16 genotype. It is important to note that although siblings may share similar repeat patterns, only identical twins will have identical profiles of repeats across the entire genome.

Diversity of Genotypes: The markers used in DNA typing commonly showcase numerous different alleles, resulting in hundreds or thousands of potential genotypes. The probability of two individuals sharing identical profiles of repeats is extremely low.

PCR Amplification: PCR products are subjected to DNA electrophoresis, which enables determination of the number of STR repeats based on the size of the DNA fragments produced.
Electrophoresis Process:
- Amplified DNA fragments are loaded into one lane of polyacrylamide gel, allowing for separation based on their size. Smaller DNA pieces migrate faster than larger ones.
- Each labeled fragment is detected as it moves past a laser at the bottom of the gel.

FBI Testing: Currently, the FBI analyzes 20 different STRs, which consist of repeats of four or five nucleotides, along with a sex marker.
- Independent Inheritance: Each STR is located on a different chromosome or at varying ends of the same chromosome, and hence, inherited independently.
List of STR Markers: Some of the tested STR markers include:
- TPOX
- D3S1358
- D5S818
- CSF1PO
- D7S820
- D8S1179
- FGA
- TH01
- VWA
- D13S317
- D21S11
- D18S51
- D16S539

Polymorphisms and Fluorescence: Each of the polymorphisms is often labeled with one of four fluorescent dyes:
- Blue
- Green
- Red
- Yellow

STR Allele Equilibrium: STR alleles maintain a state of equilibrium within populations. When the frequencies of STR alleles in a population are ascertained, one can compute the probability of inheriting a specific STR combination (genotype).
Using Population Genetics: The likelihood of a specific genotype occurring by chance can be derived using methods involving the Hardy-Weinberg principle, such as:
- $2pq$ (for heterozygous probabilities)
- $p^2$ or $q^2$ (for homozygous probabilities)
Random Match Probability: In a standard DNA profile evaluating 13 STRs, the overall random match probability is the cumulative product of the singular frequencies of each STR:
- Formula:
  $RANDOM ext{ }MATCH ext{ }PROBABILITY = STR<em>1 imes STR</em>2 imes STR<em>3 imes ext{…} imes STR</em>{13}$
- Example Calculation:
- For example, given:
  $D8S1179: 0.0586 \ D21S11: 0.0770 \ D7S820: 0.0218$
- The total probability can be computed as:
  $P( ext{Random Match}) = 0.0586 imes 0.077 imes 0.0218 = 0.000098$
- This expresses a likelihood on the order of 1 in 10,000.

Paternity Testing: Example demonstration:
- Mother
- Child
- Potential Fathers Dad 1, Dad 2, and Dad 3, indicating the probable paternal lineage based on DNA profiling outcomes.