Molecular diagnostic approaches which are being widely used in various fields including forensics. This presentation is about the different genetic factors which can be used as markers for crime scene investigation.

1. GENE LINKAGE ANALYSIS FOR
CRIME SCENE
Shabnam Ameenudeen
M. Tech Biotechnology
191442601007

2. GENETIC LINKAGE
 Genetic linkage is the tendency of DNA sequences that are close
together on the same chromosome that are inherited together during
meiotic cell division.
 This is deviated from Mendel’s Law of independent assortment.

3. GENETIC LINKAGE ANALYSIS
 Genetic linkage analysis is a tool to detect the chromosomal
location of genes.
 Genes that reside physically close together on a chromosome remain
linked during meiosis.
 They are determined by calculating the recombination frequency
(recombination events).

4. FORENSIC DNA

5. DNA PROFILING- OVERVIEW

6. CRIME SCENE- EVIDENCE
 Blood and other body fluids
 Fingerprints
 Footprints
 Hairs
 Fibers
 Tire tracks
 Drugs, chemicals, etc.

7. BASICS OF FORENSIC DNA
 Personal identification is based on biological, physiological and
behavioral characteristics.
 Most important personal identification- DNA
 The genetic similarity is 99% between humans.
 Only exception being the identical twins.

8. SOURCES OF GENETIC VARIATION
 Copy number variation (CNV)
 Interspersed elements- LINE and SINE
 Transposable elements
 Single nucleotide polymorphisms (SNP)
 Tandem Repeats- VNTR and STR

9. SHORT TANDEM REPEATS (STR)
 STR also known as microsatellites or simple sequence repeats (SSR)
 2 to 7 nucleotides in length and occurs as tandem repeats
 Highly polymorphic, 14- 15 per loci
 Powerful DNA markers for quantifying genetic variations
 100- 500bp PCR product size of STR are compatible

10. PROCESS FOR STR TYPING
 Sample collection
 DNA extraction and quantitation
 PCR amplification of multiple STR loci, STR allele separation and
sizing,
 STR typing and profile interpretation and
 Report of the statistical significance of a match

11. STR ANALYSIS/ STR TYPING
 Genotyping is performed by comparing to STR allelic ladder.
 STR allelic ladder represents all possible STR designations for a
given DNA site
 Alleles represent different lengths of STRs on a chromosome
 Sizing assured by internal sizing standard

13. Ref. Butler, J. M. (2007). Short tandem repeat typing technologies used in
human identity testing. BioTechniques, 43(4), Sii–Sv.
doi:10.2144/000112582

14. STR ANALYSIS- CRIME INVESTIGATION
 Reference and crime scene sample is compared.
 For sex identification amelogenin (AMEL) gene is checked.
 Significance of the two profiles is given by random match
probability
 The probability that DNA in a random sample is same as that of the
DNA in reference sample.
 This is based on the allele frequency.

15. FORENSIC DNA CASES
 Double rape and murder of two girls in England in 1983 and 1986
 Search for a suspect based on collection of voluntary reference
DNA sample from 5,000 local men
 One of these men, Ian Kelly, gave a sample for his friend Colin
Pitchfork and was later overheard bragging about it
 Colin Pitchfork, local baker, was subsequently tested and arrested
 The first person to be convicted based on forensic DNA evidence,
sentenced to life in prison

16. COMBINED DNA INDEX SYSTEM (CODIS)
 The CODIS is US national DNA database.
 It contains databases for:
i. Missing persons
ii. Convicted offenders
iii. Forensic samples collected from crime scene
 The CODIS offender profiling included 13 loci which are termed as
CODIS core, currently it is increased to 20.

17. SINGLE NUCLEOTIDE POLYMORPHISM (SNP)
 They are found in both coding and non-coding regions.
 It occurs in high frequency.
 PCR product size of 100- 250bp are sufficient.
 SNP in forensic analyses is categorized into:
1. Identity-testing
2. Lineage informative
3. Ancestry informative
4. Phenotype informative

18. APPLICATIONS
 The DNA profile of each individual is highly specific.
 Mass disaster victim identification
 Linking suspect to the crime
 Eliminating the suspect (false identification)
 Identifying the genetic disorders
 Paternity cases

19. REFERENCES
 Pulst SM. Genetic Linkage Analysis. Arch Neurol. 1999;56(6):667–
672. doi:10.1001/archneur.56.6.667
 https://www.sciencedirect.com/book/9780123838346/emery-and-
rimoins-principles-and-practice-of-medical-genetics
 https://academic.oup.com/bib/article/8/2/117/221568#2487407
 https://doi.org/10.2144/000112806