Epigenetic modifications often result in DNA errors
Methylation-Induced hypermutation changes definition of Epigenetics
https://jb.asm.org/content/early/2018/09/25/JB.00371-18
Excerpt from abstract: "Methylation of DNA at the C5 position of cytosine occurs in diverse organisms. This modification can increase the rate of C->T transitions at the methylated position. In E. coli and related enteric bacteria, the inner C residues of the sequence CCWGG (W=A or T) are methylated by the Dcm enzyme. These sites are hotspots of mutation during rapid growth in the laboratory, but not in non dividing cells, in which repair by the Vsr protein is effective. It has been suggested that hypermutation at these sites is a laboratory artifact and does not occur in nature. Many other methyltransferases, with a variety of specificities, can be found in bacteria, usually associated with restriction enzymes and confined to a subset of the population. Their methylation targets are also possible sites of hypermutation. Here I show, using whole genome sequence data for thousands of isolates, that there is indeed considerable hypermutation at Dcm sites in natural populations: their transition rate is approximately eight times the average. I also demonstrate hypermutability of targets of restriction associated methyltransferases in several distantly related bacteria, ranging from a factor of 12 increase in transition rate to a factor of 58. In addition, I demonstrate how patterns of hypermutability inferred from massive sequence data can be used to determine previously unknown methylation patterns and methyltransferase specificities.
IMPORTANCE: A common type of DNA modification, addition of a methyl group to cytosine (C) at carbon atom C5, can greatly increase the rate of mutation of the C to a T. In mammals, methylation of CG sequences increases the rate of CG->TG mutations. It is unknown whether cytosine C5 methylation increases mutation rate in bacteria under natural conditions. I show that sites methylated by the Dcm enzyme exhibit an eight fold increase in mutation rate in natural bacterial populations. I also show that modifications at other sites in various bacteria also increase the mutation rate, in some cases by a factor of forty or more."
My comment: Epigenetics is understood as modifiable chemical layers on top of DNA that doesn't change DNA sequence. But as we can see, this is not the case. Epigenetic modifications, such as changing DNA methylation patterns, typically lead to errors (mutations) in underlying DNA sequences. The most common genetic alteration occurring as a result from changing methylation patterns is CG --> TG mutation. This often results also in CG --> TA alterations. These are genetic errors and scientists try to repair these alterations in human genome, as we can read from here:
https://www.sciencenews.org/article/new-crispr-gene-editors-can-fix-rna-and-dna-one-typo-time
Excerpt: "Mutations that change C-G base pairs to T-A pairs happen 100 to 500 times every day in human cells. Most of those mutations are probably benign, but some may alter a protein’s structure and function, or interfere with gene activity, leading to disease. About half of the 32,000 mutations associated with human genetic diseases are this type of C-G to T-A change, says Liu, a Howard Hughes Medical Institute investigator at Harvard University. Until now, there was little anyone could do about it, he says."
Change occurring in organisms is due to epigenetic modifications and it often leads to genetic errors. This is why genetic degradation, genetic entropy is a biological fact. Evolution is not happening because there is no mechanism causing increase in biological information.
