Human mutations don't occur randomly

Epigenetic factors are linked to genetic changes

About 200,000 disease-causing genetic mutations have been discovered in the human DNA. Are these alterations random changes? Let's figure it out.


Excerpt: "Human mutations don't occur randomly. In fact, transitions (changes from A <-> G and C <-> T) are expected to occur twice as frequently as transversions (changes from A <-> C, A <-> T, G <-> C or G <-> T).

One of the most surprising features of many variant lists in humans is that C->T changes (C reference, T variant) are more frequent than T->C changes. Likewise, G->A changes are more frequent than A->G changes.

At first, this might seem a bit puzzling. For example, perhaps we might expect that the two counts should be extremely similar. However, the reference makes perfect biological sense -- and the explanation below is due to Tom Blackwell.

The major mechanism for new mutations (in warm-blooded animals) is deamination of 5'-methyl C to uracil (equivalently T) producing (C -> T) or, on the complementary strand, (G -> A). This was first studied for CpG dinucleotide sites, but it also occurs at lower rates throughout the genome at any C whether followed by G or not."


My comment: So, if an unmethylated cytosine deaminates, it turns to uracil and glycosylase, the repair enzyme, fixes this error. But if the same phenomenon occurs within methylated cytosine turning it into thymine, then glycosylase bypasses that alteration and also a G --> A transition occurs during next replication procedure. This is a mechanism.

It's clear that the level and patterns of methylation affect human genetic alterations. The most interesting phenomenon occurs at CpG dinucleotides and especially in CpG islands, genomic regions with a high frequency of CpG sites. Interesting is also, that human immune system genes typically have a clear CpG island. Seems that they were designed to experience alterations. Sounds logical.

Can we do something to keep our genes normally methylated and by this way, reduce the possibility to genetic changes? Yes, we can. Factors that mostly affect your epigenome are:

- Diet
- Stress
- Toxins
- Viruses and other pathogens

So, we can try to change our life habits by eating healthy food, avoiding stress, doing physical exercise and avoiding toxins (alcohol, smoking, chemicals etc.). It's our own choice.

Human genetic mutations don't occur randomly. Interesting is that this same mechanism is functional in almost every organism in nature. However, it will not lead to large scale evolution but it can be associated with some changes linked to the immune system . This mechanism is the most significant reason for genetic degradation. The evolutionary theory is a big lie. Don't get lost.

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