Submitted by Blakut t3_1168jbm in askscience
Let's say forensics at a crime scene only finds some cells from a human, enough to get a complete DNA sample, but not enough to get other hints about the age (e.g. no white strands of hair, hormone levels in the blood). Is it possible to get an approximate age of a person?
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What kind of accuracy does it give you? +- a year or two? Enough to confidently say the sample is from a child, adult, senior?
Median error when using multiple tissue samples is ~3.5 years but some tissues age faster and have higher error bars than others. Less than 1 year for bats.
DNA methylation age of human tissues and cell types
Measuring Animal Age with DNA Methylation: From Humans to Wild Animals
DNA methylation predicts age and provides insight into exceptional longevity of bats
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the answer is definately "No". But it may be possible in future.
We actually lose DNA as we get older. When a cell divides, its chromosomes become shorter as a small amount of DNA is lost from each end. Telomeres are long stretches of "junk" DNA at each end of the chromosome that keep important bits of DNA from disappearing. When a cell's telomeres wear out, it stops dividing.
Can we guess someone’s age from how long their DNA is?
Unfortunately, it is not that easy. Everyone is born with different DNA lengths. This means that without knowing how long someone's DNA was at birth, you can only guess their age very roughly. However, if you knew how long the person's telomere was when they were born, you could more accurately guess their age.
DNA replicates with a very high amount of fidelity (base pairs rarely get mis-matched), but it's possible to measure these mutations over time, if you had a reference sample from "x" number of years ago. Rates of mutations (and to be clear, by "mutations", I'm simply referring to the DNA polymerase making a "mistake" and the mis-matched repair not catching all of them) could probably be tracked and an age can be estimated. Is there a validated way to do this to account for all variations in someone's DNA (such as due to diet, environment, stress, etc.)? Good question!
Telomeres (ends of chromosomes) are also known to shrink over time, and this is also hard to answer in terms of "measuring" telomere ends to estimate age due to many confounding factors, but I'm sure someone is working on it.
In terms of feasibility today, telomeres YES, but mutations NO. I work in that area and will say that current technology isn’t accurate enough to spot mutations in single cells which is what you’d need (it works in cancer which have clonal expansions of mutated cells and gives you better variant call confidence). Right now sequencing error rates are too high still.
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You might in theory get an indication of the age of someone through telomeric length if you compared a sample from birth with the current sample. But I have read that telomeric length in individuals varies and rate of shortening varies it’s unlikely to be that accurate.
No, that isn't how age works.
Even for a forensic examiner, reading age from the body itself is rarely conclusive. The sole exeption is early childhood, which has specific stages of growth and therefore can be a little more telling. However, for adults or cases of malnutrition...determining an exact age is guesswork, not science. Humans do not grow uniformly.
An exact age wouldn't be possible, but in theory wouldn't it be possible to look at the number of mutations that differ between different cells in a person and match that against an expected mutation rate to get some indication of old/yound?
I'd chuck it in the MinION sequencer in the lab and start getting some data on methylation, as well as telomere length. Problem is the association between age and methylation pattern and telomere length is somewhat weak in individuals, so you wouldn't be able to get more than a hint at their age.
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[deleted] t1_j96d15v wrote
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