Health

Genetic alterations: the different causes and types

Genetic alterations: the different causes and types

Did you know that all humans share 99.9% of their genetic information? This means that our uniqueness lies in the remaining 0.1%, which varies from person to person and determines our physical characteristics (phenotype) and our response to environmental factors.

Do you want to know more? In this article, we review the different types of genetic changes that can occur in the genome, as well as advances in scientific knowledge and solutions since the complete sequence of the human genome, was publish in 2003.

Key Concepts

Did you know that all humans share 99.9% of their genetic information? This means that our uniqueness lies in the remaining 0.1%, which varies from person to person and determines our physical characteristics (phenotype) and our response to environmental factors.

Do you want to know more? In this article, we review the different types of genetic changes that can occur in the genome, as well as advances in scientific knowledge and solutions since the complete sequence of the human genome, was publish in 2003.

key concepts

To understand the possible genetic changes that create our “individuality,” let’s clarify a few key concepts. As we explain in Genes and Chromosomes:

How Do They Shape Our Life and Health? And other articles on our blog, DNA stands for deoxyribonucleic acid, a complex molecule found in the nucleus of the vast majority of cells in our body.

DNA contains the instructions for the creation and functioning of the cells of our body: from the colour of our hair to the genetic diseases that we can develop.

The DNA sequence is shown in a simplifie form according to the nucleotide base:

adenine (A)

Thymine (T)

guanine (G)

Cytosine (C)

Therefore, nucleotides are distinguish by their bases, and the DNA sequence is simplifi as A, T, C, or G, depending on the bottom of the nucleotide. DNA structure consists of two complementary strands of nucleotides that bind specifically:

A with T and C with G, forming the nucleotide base pairs of DNA. Both chains wrap around each other to form a double helix.

The central dogma of molecular biology

DNA contains the instructions, but it cannot carry out all the functions in the body on its own. Proteins are the ones in charge of carrying out these functions, and the process by which we go from DNA to a protein is captured by the central dogma of molecular biology.

In the DNA sequence, we find certain areas, called genes, that contain the information for the production of proteins. These proteins perform specific functions in the body.

There is a whole mechanism in the cells that ensures that this process is execute correctly. First, the DNA in the cell nucleus is transcribed into messenger RNA (mRNA).

In this process, the nucleotide T (thymine) is replaced by U (uracil) in the mRNA (single-stranded) that leaves the nucleus and, thanks to unique structures called ribosomes, is translated into a protein composed of an amino sequence consisting of acids.

But… if RNA is made up of a combination of 4 bases and proteins are made up of 20 different amino acids, how does translation work?

The answer lies in the genetic code, which was outlined in the 1960s and for which RW Holley, G. Khorana, and MW Nirenberg receive the Nobel Prize in Medicine.

In the mRNA sequence, the nucleotides are read in threes, forming a codon that translates to a specific amino acid, as shown in the table below. These “signals” or codons code for the amino acids that make up proteins. Among them, there are four unique signs:

AUG: marks the beginning of the translation

UAA, UAG, UGA: These are the stop codons that indicate that the translation is complete.

Finally, what is the difference between genome and exome?

The complete set of DNA in an organism called the genome. In humans, the genome contains more than 6 billion nucleotides. If we were to take the entire DNA sequence of a single cell and stretch it out, it would be over 2 meters long.

But of those 6 billion nucleotides, only a tiny fraction (about 2%) is current known to contain protein-forming information, and that tiny fraction is the exome. Therefore, we refer to the exome as the coding region of DNA, while the rest comprises non-coding areas that do not contain information for protein synthesis.

So if it doesn’t code for proteins, what is the function of non-coding DNA? Long considered ‘junk DNA’, scientific advances have shown that non-coding DNA has multiple functions, the most important of which is regulating the expression of other genes.

What are genetic alterations?

Any change in the DNA sequence can alter the genetic code and, therefore, can change the synthesis of the protein it codes for.

For example, if we look at the genetic code table, the CAA codon translates to the amino acid glutamine. In contrast, AAA translates to lysine, so change one nucleotide for another (C for A) changes the composition of the protein, which could affect its function.

But when the change is to UAA, this is a stop codon instead of generating glutamine and stops protein synthesis.

Therefore, the clinical relevance of a genetic change depends on where it occurs, i.e. whether or not it takes place in the coding region (exome) and whether the change results in a dramatic change in protein synthesis and, thus, therefore, its function in the body of the gene.

What sort of changes might occur?

The example shown above is a substitution, as one nucleotide is exchange for another, but there are other types of genetic changes, more generally:

Substitution: one base in exchange for another.

Deletion: Removal of some commands.

Duplication: Duplication of a part of the bases.

Reversal: Reverse the order of a base sequence.

Why do genetic alterations occur?

Almost all cells in the human body are regularly replace. To do this, the cells divide into two daughter cells. During this division process, errors can occur that lead to genetic changes. External factors like smoking exposure to sunlight and many others increase the probability of such errors. We call these mutations somatic because they only affect the cell where the error occurred and are not pass on to offspring.

But genetic changes can also be present from birth. If the egg or sperm cell has a congenital disability, it is transmitt to the zygote and thus appears in all its cells since all the cells of the “new” human come from this “original” cell.

It is also possible that the change occurs during embryogenesis (the transformation process from zygote to embryo) even though it does not happen in the sex cells. In either case, these changes are call germline mutations, and people who have them can pass them on to their offspring.

Genetic alterations, mutations and polymorphisms

Mutations

I’m sure you’ve heard of mutations and probably negatively associated with the term. There a reason for this because mutations are genetic changes that occur in less than 1% of the population and are associate with increase disease risk.

For example, you have probably heard of the BRCA1 gene. The function of this gene is to control cell division to prevent tumours properly.

A mutation in this gene leads to uncontrolled cell division, which increases the risk of tumour development. More specifically, people with a BRCA1 mutation have a 46% to 87% lifetime risk of developing breast cancer.

Read More:- 7-health-tips-for-your-physical-and-mental-well-being

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