The topic of this fascinating article might not be directly a gene-environment interactions topic, per se, but it’s worthy of sharing with all of GEITP — because it shows how far DNA analysis in Criminology has come.😊 On the news every day, we see and/or hear “At the scene of the crime, samples were taken from the door knob, the Glock pistol, the handle of the kitchen knife, and the crow bar — and sent to the lab for DNA analysis.” What does the “DNA analysis” usually entail? And how specific do the DNA tests have to be — as far as proving the suspect was 100% likely to have committed the crime?
Humans have 3% to 5% of their genomic sequence composed of more than a million Short Tandem Repeats (STRs) — which (in the 1980s) were considered as “junk DNA.” STRs are short, 1– to 6-base pair DNA sequences (repeated in head-to-tail fashion throughout the human genome). Examples of such STRs would include:
TTTTTTT GTGTGTGT GTCGTCGTC ATTCATTCATTCA TATCCTATCCTATCC ATGCATATGCATATGCAT
During the S phase of the cell cycle, DNA is replicated — to ensure that each daughter cell receives an identical set of chromosomes. The process is “semi-conservative,” meaning that the double helix is unwound by enzymes (helicases), and each of the two strands serves as a template for a new complementary strand, resulting in two DNA molecules, each with one old and one new strand. The number of repeats varies between individuals and ethnic groups, but those variations are quite constant among people who are related. Occasionally, however, an insertion or deletion occurs (due to “slippage” of the DNA sequence during replication that occurs during cell division). Consequently, the lengths of each of our STRs can sometimes vary — serving as a good reason to test some (particularly “popular”) STRs for DNA fingerprinting, forensic identification, and paternity testing. The attached article says “up to 30 regions of STRs is generally tested by PCR analysis.”
Also, abnormal expansions of these repeats have been associated with risk of certain human genetic disorders — including neurological conditions such Huntington disease, fragile X syndrome, amyotrophic lateral sclerosis (ALS), frontotemporal dementia, and spinocerebellar ataxias — as well as several types of cancer, autism spectrum disorder (ASD), and schizophrenia.
The attached article describes a case in which DNA from an identical (monozygotic) twin was found to be the culprit — and how the clinical lab can go about determining [whole-genome sequencing (WGS; gDNA), mitochondrial DNA (mtDNA), and the whole-genome methylome] which of the two males is the criminal. 😊
As an aside (and this makes for great cocktail conversation!!) — did you know that, as the fertilized egg (zygote) divides four times into 2, 4, 8, & 16 individual embryo cells — up to the 16-cell stage, it is possible to extract any of these 16 cells and still create an intact normal human being…!! This begs the (theological) question: “WHEN does the soul enter the embryo?” Or “Are there 16 souls originally, and 15 of them are usually discarded?” 😉😉
DwN
doi: https://doi.org/10.1038/d41586-026-00521-z Nature
https://www.nature.com/articles/d41586-026-00521-z?utm_source=Live+Audience&utm_campaign=a515d67d93-nature-briefing-daily-20260305&utm_medium=email&utm_term=0_-33f35e09ea-51775244