DNA Structure and Cell Division

The Structure and Definition of DNA

• DNA (Deoxyribonucleic Acid) is a double helix, identified in 1953 by Francis Crick and James Watson, with contributions from Rosalind Franklin and Maurice Wilkins.
• Rosalind Franklin's Photo 51 in 1952 played a crucial role in revealing DNA's structure.
• DNA consists of nucleotides that include adenine (A), thymine (T), guanine (G), and cytosine (C), forming the genetic blueprint of all living cells.
• Nucleotides pair specifically: A with T and G with C, stabilization is aided by Van der Waals forces.
• DNA's helical structure protects its information, with sequences forming genes.

Chromosomes and Cell Division

• DNA is organized into chromosomes; human karyotypes contain 22 pairs of autosomes and one pair of sex chromosomes.
• Accurate DNA replication is essential for cell division; errors can result in death, disease, or cancer.
• Mitosis creates identical daughter cells for growth and repair, while meiosis generates gametes (sperm and egg) through division into four cells.

DNA in Law Enforcement

• DNA fingerprinting was pioneered by Sir Alec Jeffreys in 1984, initially utilized in a 1985 immigration case.
• The CODIS (Combined DNA Index System) tracks profiles of convicted offenders, arrestees, and missing persons.

STRs vs. SNPs

• Short Tandem Repeats (STRs) are analyzed in CODIS, while Single Nucleotide Polymorphisms (SNPs) are used in Direct-to-Consumer (DTC) databases for genetic genealogy.
• Both involve DNA extraction but differ in analysis and application, with genetic genealogy expanding upon initial CODIS findings.

Steps in Genetic Genealogy

• Four main steps include:
  • Find: Identify the best DNA matches.
  • Create: Construct family trees for these matches.
  • Group: Figure out how the trees are interconnected.
  • ID: Integrate your DNA into the established trees.

DNA Segment Triangulation

• Triangulation occurs when three individuals match on the same DNA segment, indicating they share a common ancestor.
• This technique is vital for tracing the lineage, particularly for adoptees seeking birth parents.

Case Studies in Genetic Genealogy

• The Niskayuna arrest of Stephen Smerk involved forensic DNA technology that led to his identification in the cold case of Robin Lawrence's murder.
• The NorCal Rapist case was solved swiftly through a close DNA match within 45 minutes, showcasing the efficiency of modern genetic techniques.

Estimated Time to Solve Cases by cM Matches

• Approximate time to solve cases varies with centiMorgans (cM):
  • 3500 cM indicates a parent (solving takes hours).
  • 2500 cM signifies a sibling.
  • 900 cM points to a 1st cousin (days to weeks).