Human Genetics

Understanding Human Genetics

Genetics is the study of how living things inherit certain traits from preceding generations. These traits are carried by a molecule known as DNA (deoxyribonucleic acid). Every living thing contains DNA. Genes are hereditary units which consist of DNA.

They occupy spots on chromosomes – threadlike structures composed of protein and nucleic acids found in the nucleus of most living cells – and determine an organism’s characteristics. The whole set of genes constitutes a genome.

A human being contains around 21,000 genes and virtually all of a person’s characteristics are defined by the coding of proteins by the genes. These characteristics include blood groups and the colours of eyes and hair. Some characteristics do not depend on genes alone.

For example, you may inherit “tall” genes from your parents but if your diet is poor and you consume an insufficient amount of nutrients, your growth may be stunted. Genes may also determine whether or not you are more likely to contract any of a range of medical conditions. Many of these occur when an altered (or mutated) type of gene is passed from one or both parents to the child.

The origin of the study of genetics can be traced back to the work of Charles Darwin and his research into the origin of species along with that of Alfred Russel Wallace.

Whilst these two were known for their pioneering work on the theory of evolution it was their contemporary, the Austrian monk Gregor Mendel, whose pea plant experiments, conducted between 1856 and 1863, who established many of the rules of heredity – the passing of traits from parents to offspring. Although scant awareness was paid to Mendel’s work during his lifetime, this discovery went on to become the foundation of the understanding of genetics as we know it today.

In later years, the German naturalist Ernst Haeckel identified the nucleus cell as being vital to the evolutionary process and the Swiss physician Friedrich Miescher became the first researcher to prove the material contained within the nucleus was a nucleic acid.

Discoveries continued into the twentieth century. To cite just a few examples, in 1902, Walter Sutton and Theodore Boveri discovered chromosomes, with their work corresponding to Mendel’s original findings. In 1905, Nettie Stevens discovered the X and Y chromosomes which determine gender. (Y chromosomes produce male offspring and those embryos without Y chromosomes will be female) In 1944, Oswald Avery identified DNA as genetic material and observed how DNA can transfer genes into bacteria cells. In 1953, Francis Crick and James Watson determined the structure of DNA (the double-helix) and the DNA code was discovered and deciphered in the 1960s by Marshall Nirenberg, Har Gobind Khorana and Robert W. Holley.

The speed with which discoveries in the field of genetics were made was impressive, with just over one hundred years passing between Mendel’s original discovery (and just over fifty since his research emerged from obscurity) and the Nobel-winning deciphering of the DNA code.

Following these discoveries, the question soon began to revolve around what should be done with the knowledge acquired. Now that some understanding of genes had been gained, the logical next step was to uncover how to replicate and manipulate it. In 1958, Arthur Kornberg and Severo Ochoa discovered an enzyme in bacteria which enabled them to synthesise ribonucleic acid (RNA). This paved the way for genetic engineering.

Genetic engineering consists of the following steps. First, the desired characteristic is selected and it is then cut out of the chromosome. Next, the gene is inserted into another organism before the modified organism is replicated. A common example of genetic engineering are plant crops which are engineered to be resistant to diseases.

These are known as genetically modified crops. The potential benefits of genetic engineering are considerable. Genetically modified crops, for example, could be used to increase the yield and quality of crops, which could go a long way towards alleviating world hunger. However, there are also risks and drawbacks.

Toxins from GM crops have been found in the bloodstreams of people who have consumed them for one and the seeds for them are more expensive than those of non-GM crops, thus potentially pricing them out of people in developing countries.

One exciting offshoot of genetic engineering is gene therapy. Although largely still in the experimental stage, this technique is intended to use genes to treat and even prevent diseases. In the future, gene therapy may enable doctors to treat illnesses by inserting healthy and uncorrupted genes and removing those that are mutated.

At the time of writing, gene therapy is considered an extremely risky procedure and is generally tested with diseases that have no known cure. Research is currently underway into whether genetic engineering may be able to one day produce effective treatments of hereditary ailments such as cystic fibrosis and Huntingdon’s Disease.

It is hoped that one day various forms of cancer and viral infections may also prove to be treatable by such a method.

From such humble beginnings, the scientific field of genetics has made major advances in a relatively short space of time. It has provided us, and continues to provide us, with a considerable amount of knowledge relating to what materials make up our bodies and how we develop our personal characteristics.

As research continues, new treatments for diseases either become available or take one step closer to becoming reality. The revelations from genetics have so far proven to be ground-breaking and there is no reason to suggest that we are nearing the end of our discoveries in this field. We may not even be past the beginning.

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