It is the means by which instructions are transmitted from one generation of organisms to the next.
In life on earth, it takes the form of nucleotide sequences that are organized into genomes. A genome is all the DNA contained within the cell of a living being. Each human DNA molecule has billions of nucleotides arranged as steps on a ladder.
It is the nucleotide sequence that determines the features of the organism. In several places, called loci, along each chromosome, between large extensions of non-coding sequences, the nucleotide DNA sequences are resolved into coherent patterns that instruct the messenger proteins on how to build other proteins.
These proteins are synthesized in the cytoplasm of the cell and work to build all the structures of a living body. Genes, as a natural consequence of their nucleotide sequences, build proteins and build protein bodies.
The genetic material is transmitted to large organisms by vertical transmission from parents to children.
Each offspring looks more like its parent than a member of its species chosen at random because the exact sequence of genetic instructions on how to build the body has been inherited from the father.
Small errors in gene copy are known as mutations, and their proliferation along a set of genes drives the process of evolution.
DNA fulfills two essential functions that deal with cellular information. First, DNA is the genetic material responsible for the inheritance and is transmitted from parents to children for all life on earth.
To preserve the integrity of this genetic information, DNA must be replicated with great precision, with minimal errors that introduce changes in the DNA sequence.
A genome contains the complete complement of DNA within a cell and is organized into smaller and discrete units called genes that are arranged in chromosomes and plasmids.
The second function of DNA is to direct and regulate the construction of the proteins necessary for a cell to grow and reproduce in a particular cellular environment.
A gene is made up of DNA that is “read” or transcribed to produce an RNA molecule during the transcription process.
An important type of RNA molecule, called messenger RNA (mRNA), provides information for the ribosome to catalyze the synthesis of proteins in a process called translation.
The processes of transcription and translation are collectively referred to as gene expression. Gene expression is the synthesis of a specific protein with an amino acid sequence encoded in the gene.
The flow of genetic information from DNA to RNA to protein is described in the central dogma. This central dogma of molecular biology further elucidates the mechanism behind the hypothesis of “a single gene-an enzyme” of Beadle and Tatum.
Each one of the processes of replication, transcription and translation includes the following stages:
- Elongation (polymerization).
The genotype of a cell is the complete collection of genes it contains, while its phenotype is the set of observable characteristics that result from those genes.
The phenotype is the product of the set of proteins produced by the cell at a given time, which is influenced by the genotype of the cell, as well as by interactions with the cell environment.
Genes encode proteins that have functions in the cell. The production of a specific protein encoded by an individual gene often results in a different phenotype for the cell compared to the phenotype without that protein.
For this reason, it is also common to refer to the genotype of an individual gene and its phenotype. Although the genotype of a cell remains constant, not all genes are used to direct the production of their proteins simultaneously.
The cells carefully regulate the expression of their genes, using only genes to produce specific proteins when these proteins are needed.
Use and abuse of human genome data
Why do some humans harbor opportunistic pathogens such as Haemophilus influenza, Staphylococcus aureus or Streptococcus pyogenes in their upper respiratory tract, but they remain asymptomatic carriers, while other individuals become seriously ill when they become infected?
There is evidence to suggest that differences in susceptibility to infection among patients may be the result, at least in part, of genetic differences among human hosts.
For example, genetic differences in human leukocyte antigens (HLA) and red blood cell antigens between hosts have been implicated in different immune responses and disease progression resulting from H. influenzae infection.
Because the genetic interaction between the pathogen and the host can contribute to the results of the disease, understanding the differences in genetic make-up between individuals can be an important clinical tool.
Ecological genomics is a relatively new field that seeks to understand how the genotypes of different organisms interact with each other in nature. The field answers questions about how the gene expression of one organism affects the gene expression of another.
The medical applications of organic genomics will focus on how pathogens interact with specific individuals, unlike humans in general.
Such analyzes would allow medical professionals to use the knowledge of an individual’s genotype to apply more individualized plans for the treatment and prevention of the disease.
With the advent of next-generation sequencing, it is relatively easy to obtain all the genomic sequences of pathogens; A bacterial genome can be sequenced in just one day.
The speed and cost of sequencing the human genome have also been greatly reduced, and individuals can send samples to receive comprehensive reports on their personal genetic characteristics, including ancestors and the carrier status of various genetic diseases.
As the sequencing technologies progress further, these services will continue to be less expensive, more extensive and faster.
However, as this day approaches, there are many ethical concerns with which society must contend.
Should genome sequencing be a standard practice for everyone?
There are many questions. Should the law or employers require you to reduce the costs of medical care? If you reject genome sequencing, do you lose your right to health insurance coverage? For what purposes should the data be used?
Who should supervise the proper use of this data? If genome sequencing reveals a predisposition to a particular disease, are insurance companies entitled to raise rates? Will employers treat an employee differently?
Knowing that environmental influences also affect the development of the disease, how should data on the presence of a particular allele causing disease in an individual be used ethically?
The Genetic Information Nondiscrimination Act of 2008 currently prohibits discriminatory practices based on genetic information on the part of health insurance companies and employers.
However, it does not cover life, disability or long-term care insurance policies.
Clearly, all members of society must continue to participate in conversations on these issues so that such genomic data can be used to improve medical care while simultaneously protecting the rights of people.