Genetics

Genetics is the study of how traits are encoded in DNA and passed from generation to generation.

The foundations for this scientific field were established by Gregor Mendel, a mid-nineteenth century monk whose experiments in breeding peas revealed the inheritance patterns of certain traits, such as pod colour or wrinkly seeds. Through these experiments, he was able to determine that some traits are dominant, and others recessive.

Today, we know that such traits are caused by different variants of the same gene, known as alleles. Genes are the regions of DNA that code for proteins, but their specific code can vary. Humans and various other – but not all – organisms have two copies of almost every gene, one from each of their biological parents.

These alleles can cause disease. For example, Huntington’s chorea is a dominant disorder, meaning people only need to inherit one copy of the Huntington’s allele to develop the condition. Cystic fibrosis, however, is a recessive disorder – a person must inherit two cystic fibrosis alleles to have the condition.

It took a while for Mendel’s work to gain the recognition it deserved. One proponent of his findings was the biologist William Bateson, who introduced the word “genetics” in 1905.

In the mid-twentieth century, biologists and mathematicians combined Mendel’s conclusions on inheritance with Charles Darwin’s theory of natural selection, in a movement known as the modern synthesis. This school of thought revolutionised our understanding of biology, transforming it from a discipline defined by observations and specimen collecting to a field underpinned by unifying principles and a mathematical framework.

In the decades that followed, the structure and function of DNA was determined, and we now understand how genes work, how they are passed down the generations, and how they mutate and evolve.

We now know that, in addition to single-gene traits like cystic fibrosis in people or wrinkly seeds in peas, a large number of traits are governed by multiple genes. One human example is height.

In addition to this, many traits are even more complex, being governed not only by many different genes that each have a tiny effect, but also being influenced by the environment that we live in. Intelligence and obesity are two examples of these.

To unpick the role of genes, geneticists use sophisticated statistical methods. Calculating the heritability of a trait, by tracking it in a population, gives an idea of the degree to which variation in that trait is attributable to genetics, rather than environmental conditions. Twin studies enable researchers to further determine the extent to which genes might be responsible for certain traits. Genome-wide association studies can be used to sift through data to pinpoint genes that seem to be associated with certain characteristics.

As our understanding of genetics has advanced, we’ve been able to develop new scientific techniques based on genes. Genetic modification involves inserting new genes into an organism, to give it additional traits or abilities, such as pesticide resistance. Gene therapy has been developed as a treatment for some single-gene disorders, and works by administering functional copies of particular genes to people who have faulty alleles.

Until recently, modifying the DNA of humans and other organisms has been a difficult and laborious task, but new gene editing techniques such as CRISPR mean that we can now change genes much more easily. If these techniques can be made safe enough for use in people, they could lead to significant new medical treatments, but also open the door to human enhancement – genetic changes designed not to treat disease, but to improve our appearance or abilities. Penny Sarchet