Lecture #18 | DNA Analysis

Importance of DNA analysis in forensic cases

• Recently has been successfully used to solve cold cases and exonerate previously convicted individuals

  • Very small quantities of DNA can be amplified, so great care must be taken to ensure that evidence samples are not contaminated by other DNA

Process of DNA analysis

1. Sample collection

2. DNA extraction

3. DNA amplification

4. DNA analysis and interpretation

What parts of DNA are used in identification?

1. STR: Short Tandem Repeats: Hypervariable regions in genome

2. SNPs: Single nucleotide polymorphisms: Variations at single DNA base

3. MtDNA: Persists in degraded DNA sample. Compare to material lineage

What information is provided by the national DNA database?

Convicted offenders at the national, state, and local level

How can DNA analysis be used for identification?

Identification is important for PMI estimation

• ID by morphology alone is difficult for some insects

Barcode of Life (BOLD)

the COI gene

• BOLD has many published sequences of this gene

Challenges:

• Some species cannot be separated easily due to similar COI sequences

How does DNA vary by insect population?

Differences are detected by variation in DNA sequences usually of multiple gene sites

• May suggest relocate of a corpse

Importance of gut content in DNA analysis

1. Corpse identification

   1. Necrophagous insects may retain DNA from corpse cells

2. Bloodmeal identification

   1. Does DNA match suspect, witness

   2. Limited window of time as insects digest blood within 24-72 hrs