Could identical twins commit the perfect crime? | Veritasium

The Gist

Identical twins can be convicted of crimes by using whole genome sequencing to find tiny genetic mutations that occur during cell division. Although standard DNA tests match both twins, sequencing all three billion base pairs can reveal about five differing positions.

Quick Overview

Whole genome sequencing solves the forensic puzzle of identical twins by identifying the rare single letter genetic mutations that separate their DNA over time. Standard forensic DNA profiling fails because monozygotic twins share the same initial genetic code, allowing suspects in cases like a luxury store robbery in Germany to walk free. While copying errors during cell division create a handful of differences across three billion base pairs, the method remains expensive and requires sufficient physical evidence like a pool of blood.

Key Points: Identical twins share the exact same DNA at birth because they develop from a single fertilized egg. Standard police DNA tests yield matching profiles for both twins, leaving law enforcement unable to prove which individual committed a crime. A notable real world case in Germany involved twin brothers who robbed luxury stores and walked free because prosecutors could not prove who did it. Monozygotic twins do not stay identical throughout their lives because copying errors occur every time cells divide. A single letter in the genetic code can get swapped during cell division, creating differences across three billion base pairs. Whole genome sequencing reads all three billion base pairs to pinpoint roughly five distinct genetic positions between identical twins. The genetic identification method requires expensive sequencing technology and sufficient DNA samples, such as a puddle of blood left at a crime scene.

Context: Forensic science has long relied on DNA profiling to identify suspects at crime scenes, but identical twins present a unique loophole because standard tests cannot distinguish between them. This investigation explores how advanced genetic sequencing pushes past the limits of conventional forensics to catch criminals who hide behind their twin sibling.