A workforce led by researchers on the Johns Hopkins Faculty of Medication has discovered that a number of inherited traits within the mouse genome break the foundations Gregor Mendel laid down within the nineteenth century about how genes work. This isn’t as a result of the genes mutate however due to chemical modifications of the genome that may bounce throughout generations, change relying on whether or not an animal is male or feminine, and even copy themselves from one copy of a gene to a different.
Their findings have been reported lately in Nature Genetics.
Whereas the research was in mice, the implications go far past — as the identical mechanisms might also form human well being, and be capable of clarify situations which have lengthy resisted genetic evaluation.
‘On’ and ‘off’ genes
Each cell within the physique carries two sorts of genetic info. One is the sequence — the order of the 4 chemical bases, A, T, G, and C, that spells out which proteins a gene produces. That is the genome that geneticists have spent many years mapping. The opposite is about whether or not a small chemical compound — known as the methyl group (–CH3) — is connected to the DNA at particular areas.
When cytosines are methylated, the gene is normally silenced. When the group is eliminated, the gene might be expressed once more. This technique of switching genes ‘on’ and ‘off’ with out altering the underlying sequence is named epigenetic modification.
Epigenetic modifications usually are not everlasting. They will even differ between tissues — e.g. liver cells and muscle cells methylate in a different way. Lots of them are additionally reversed when the physique makes recent sperm or eggs.
The brand new research has discovered this rule to be violated.
An illustration of cytosine and methylated cytosine.
| Photograph Credit score:
Mariuswalter (CC BY-SA)
Vastly underestimated
The researchers used a expertise known as nanopore sequencing. A single strand of DNA is threaded via a microscopic gap — the pore. As every base passes via, it produces a definite blip within the electrical present flowing throughout the pore. Methylated cytosines produce a distinct blip from unmethylated ones.
The workforce sequenced DNA from the liver and muscle tissues of mice belonging to 2 inbred strains. Their genomes differed at hundreds of thousands of positions.
Of the 7,600 or so areas on the genomes the place the methylation patterns differed, round 93% adopted Mendel’s guidelines. That’s, methylation had handed reliably from father or mother to offspring. However within the remaining 7% or so, the researchers recognized greater than 500 situations of non-Mendelian epigenetic inheritance.
For example, in 305 genome areas, all within the liver, the methylation trusted whether or not the mouse was male or feminine. Mendel’s guidelines don’t permit this. In 304 of those areas, females’ genomes have been extra methylated than males’ genomes.
Whereas sex-specific methylation within the liver has been reported earlier than in each mice and people, the brand new research discovered that the dimensions has been vastly underestimated.
A brand new first
The researchers additionally recognized no less than 5 new genes displaying genomic imprinting — the place the extent of methylation is determined by whether or not the gene was inherited from the mom or the daddy.
Essentially the most hanging discovering needed to do with a phenomenon known as paramutation. Right here, the methylation standing of 1 copy of a gene — say, the one inherited from the daddy — can be transferred to the opposite copy, inherited from the mom. The ‘rewritten’ mom’s copy then persists via the following technology.
Once more, scientists had noticed paramutation in crops and engineered mice earlier than. That is the primary time it has been reported to be naturally occurring in a mammal’s genome.
Within the research, the paramutated gene was Capn11, which accommodates the recipe for a protein that’s energetic within the testes throughout meiosis. When this protein isn’t out there in ample quantities, the results could embody infertility and azoospermia (having no sperm within the semen).
The workforce additionally recognized two probably situations of paramutation associated to the gene Vps37c and a downstream stretch of the genome. Each these areas are related to intracisternal A particles — the genetic stays of historical viruses that grew to become embedded within the mouse genome.
In response to the research’s authors, these particles could also be central to the paramutation course of since they’ve been recognized to withstand the physique’s mechanisms to take away epigenetic modifications when producing sperm or eggs.
Genome-wide affiliation research
The research additionally presents a brand new framework to clarify heritable traits that researchers have struggled to check utilizing genetics. As an illustration, a situation known as hypertrichosis pinnae auris results in the expansion of coarse, darkish hair on the outer ear and is prevalent amongst South Asian males. It’s transmitted from fathers to sons however by no means to daughters.
In response to the research’s outcomes, if a father carries a paramutagenic model of the gene that causes this situation and the mom carries a ‘regular’ model, then in a son the paramutagenic copy would rewrite the maternal copy, leaving the son to have bushy ears. He may then move the paramutagenic variant of the gene to his personal youngsters. But when the paramutagenic variant is demethylated in females — as the brand new findings recommend can occur — a daughter’s personal copies of the gene could be unmethylated and her ears could be unaffected.
Much more broadly, the findings suggest that genome-wide affiliation research — an more and more well-liked type of research that appears for the genetic variants linked to ailments — could also be lacking a major fraction of heritable variation as a result of that variation isn’t within the sequence. As an alternative, the research’s authors have argued, the work opens the door to a brand new type of evaluation: allele-specific epigenome-wide affiliation research, which hint methylation patterns slightly than sequence variants, to seek out elements of the genome related to ailments that standard strategies miss.
Human genetics has lengthy assumed that should you sequence the genome, you have got learn the instruction handbook. It might be that the handbook has a second quantity — and we have now barely opened it right now.
D.P. Kasbekar is a retired scientist.
Printed – August 10, 2026 09:00 am IST
