🧬 DNA, Chromosomes & Forensics – Study Guide

Chromosome | A tightly coiled structure of DNA and proteins that carries genetic information
Number of human chromosomes | Humans have 46 chromosomes (23 pairs)

Monomer of DNA | Nucleotide
Nucleotide components | Phosphate group, deoxyribose sugar, nitrogenous base

Adenine (A) | Pairs with Thymine (T)
Thymine (T) | Pairs with Adenine (A)
Cytosine (C) | Pairs with Guanine (G)
Guanine (G) | Pairs with Cytosine (C)

Antiparallel strands | DNA strands run in opposite directions (5′→3′ and 3′→5′)
How to identify antiparallel strands | One strand goes up, the other goes down

🔁 DNA Replication

Purpose of DNA replication | To copy DNA so each new cell gets identical genetic information

Helicase | Unzips DNA by breaking hydrogen bonds
Primase | Adds RNA primers to start replication
DNA polymerase | Builds new DNA by adding complementary nucleotides and proofreading
DNA ligase | Connects DNA fragments together

Leading strand | Made continuously toward the replication fork
Lagging strand | Made in short pieces called Okazaki fragments
Why leading and lagging strands occur | DNA polymerase can only build DNA in the 5′→3′ direction
How to identify leading strand | Smooth, continuous strand
How to identify lagging strand | Fragmented strand with primers

Semi-conservative replication | Each new DNA molecule has one original strand and one new strand
Template strand | Original DNA strand used for copying
Complementary strand | New strand built to match the template

🧪 Roy Brown Case (Forensic Science)

Roy Brown case | A man wrongfully convicted of rape in the 1990s
Accusation | Rape based on bite mark and hair evidence
Bite mark evidence | Later shown to be unreliable and inaccurate
Hair analysis evidence | Not scientifically reliable; led to wrongful conviction
What freed Roy Brown | DNA testing proved his innocence