DNA Structure and Cell Division

Study Notes

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).

Description

Explore the essential concepts of DNA structure, including its double helix formation and nucleotide pairing, as well as its organization into chromosomes. Understand the processes of mitosis and meiosis, which are vital for growth and reproduction in living organisms.