GENE WORLD ISSN 2755-9971 (online).

Issue One, 27th November. Volume 1 (2022).





From Apples to Genes

By Helen Gavaghan

Throughout history people have seen resemblance between and among family members. The saying, "the apple never falls far from the tree" entered common usage, proving later to be a deeply unhelpful insight into commonalities among organisms. For example, successive generations may have different reasons for developing an illness such as bowel cancer (1), though illness in other family members can be a strong indicator that genetic testing might help guide screening and preventive strategies.

Perhaps the first comprehensive effort to deal with intergenerational biology comes from Aristotle (384-322 BCE). In a world without knowledge of DNA and genes he did what all good scientists do: he observed and tried to systematize the natural world. Though Aristotle's answers may to the modern mind seem wrong, they foreshadow systematic classification of organisms, organism development, and passing traits to offspring (2).


The first to make sense in a way the modern mind comprehends of how characteristics pass from generation to generation was Gregor Mendel (1822-1884), father of genetics. He discerned there must be some kind of entity responsible for what he observed when growing peas. Mendel learned of dominant and recessive traits. We now know dominance results when both parents carry a gene for a simple trait such as eye colour. Brown is dominant, blue is recessive. If two brown eyed parents have a blue eyed baby, then it is likely (not absolute) that all the grandparents had a gene for* blue eyes. For a recessive trait to be expressed, both parents must have contributed a blue eyed (recessive) gene. Brown eyed babies need only one parent to contribute a gene for brown eyes.

Mendel's genius was selection of a manageable experimental set up to test ideas of inheritance. Working with peas, and looking at simple pea traits, such as rough and smooth seed coats, Mendel worked out there must be some segregation of an entity passing on characteristics. That is a giant leap of thought for biology. A plant species with more complex genetics would not easily have yielded the idea of some physical entity - which we now call a gene - which can carry attributess forward predictably. It seems to me Mendel must have observed a lot of less obligingly predictable species before alighting on pea biology as a way of prying open the door to explore inheritance. With his experimental species selected, Mendel then grew a lot of peas. He deduced from data simple rules about passing down the generations certain aspects of an organism's biology.

Later, in 1909, Mendel's observations enabled the concept of a gene to develop in the intellectual world. Gene was the name given to the thing carrying forward biological information like seed smoothness in peas. Then came Barbara McClintock (1902-1992). She grew corn. Corn traits such as kernel colour do not obey Mendelian rules in as compliant a fashion as peas (3). From McClintock we learned of jumping genes, but still did not know what this thing called a gene was made from. Jumping genes (jumping around for the most part on chromosomes) were seen to lead to more varied breeding outcomes. We now refer to jumping genes as transposons, and their expression is influenced by the position they have jumped to on a chromosome. If corn had been studied before peas, it would have been much harder to discern a pattern that could have led to the concept of dominant and recessive gene traits and Mendelian simple predictable inheritance, and so to an understanding of how such patterns are modified. Deep mechanistic understanding of McClintock’s observations and of gene behaviour and control on chromosomes and in-situ in living cells is still developing.

This is not unusual in science: to see something ineffable in the natural world and to seek to tether that observation with words, hypothesis and, finally, experimental proof. In science, we reify theories about the working of the natural world. Move your plants around your home, and watch them respond to light, draught, water, and varied nutrients. Often in science we give a name to something that informed observation suggests must exist, even though we give it a name before knowing what that thing is, and what its complexities and limitations are. In the world of physics, we have assigned the name quark to something invisible to people - just as a gene is invisible to the human eye. We are still learning from a quark's impact on and interaction with the natural world what all the attributes and forms of a quark are. Again, the same is true of genes. What was once a simple Mendelian concept (Mendel did not use the word gene) has now become a jumping, twisting, flipping, splitting, cartwheel-turning piece of the natural world. Genes can be more complicated than even McClintock thought. But be they never so wiley, genes cannot escape the rules of chemistry and physics in biology!

We now know complex (sometimes called quantitative) traits exist in plants and animals. They have the catchy acronym "QTL", and are of great interest to farmers and the agricultural sector of business. Quantitative traits are phenotypes, where a phenotype is an expression of our genetic nature. Phenotypes are written in our DNA. Multiple genes can interplay and be influenced by the environment. How chemically and physically is that possible? We are at the beginning of the modern biological investigation of that question.

The breakthrough which seems set to reverberate to the end of biology on Earth came in the middle of the last century. That was when we learned DNA is the stuff of the gene, and that DNA has a structure which enables it to pass its biological information on, and from one cell to its replacement cell/cells as an organism grows and lives.

As the 20th century progressed, we learned how RNA is a key in extracting information about our biology from DNA. DNA and RNA are the conductor and first violin of and in the orchestra of life, within environment, and between succeeding generations. We learned about DNA first, though for a while it was thought proteins rather than DNA might carry life's message forward. Now we know proteins, carbohydrates, and lipids (fats) add nuance to a pas-de-deux DNA and RNA dance every moment an organism lives. Between them, DNA and RNA keep us alive. That is true of most biology, other than in those organisms, such as some viruses, which store the genetic message in RNA only. Viruses, as the world has learned to its cost during the Covid pandemic, hijack biology to pass on their message. They are otherwise impotent.

DNA is better known to the public than is RNA, though a good forensic science mystery might remedy that imbalance one day. Some of DNA's subunits form the code containing the genetic information passed from generation to generation, and DNA has become a common word in the modern lexicon. The DNA message might be to make a human, to create a walrus, or build a chrysanthemum.

RNA, DNA's dance partner, carries DNA’s message into and around the cells that are the basic unit of all biology. As with DNA and genes, there was a time before cells were known to exist, and before they were seen for what they are, namely squishy, deceptively complicated, self-contained, living but non-conscious elemental parts of our being and of all biology. Somehow, from the natural world, cell walls and plasma membranes emerged to make cells intact. Biology did not manufacture, programme and direct creation of these cell boundaries. Rather, through the workings of the forces in biology, chemistry and physics the boundary walls making cells possible emerged. Then within the cells, DNA, RNA, proteins, lipids, and carbohydrates can carry on undisturbed the business we call living.

DNA and RNA can match each other, subunit by subunit. But RNA is a slightly less stable molecule chemically than DNA. The difference means RNA can be more easily split into varying lengths, and can facilitate tasks around the cells which would be beyond the reach of the more stable DNA. Stability and flexibility – the perfect dance partnership! Now we know in differing molecular lengths RNAs make up a corps-de-ballet. Can you imagine Swan Lake without the Corps-de-Ballet? The story would be very different. So, too, the story of DNA, and biological evolution, and development on Earth would be very different without RNA.

DNA, nevertheless, is the principal. Disruption of DNA can have devastating consequences. Remember the abnormal foetal development which the drug thalidomide caused? By understanding how DNA and RNA, proteins, lipids, carbohydrates, plasma membranes and cell walls are constructed and work together within an organism, such human-made disasters can be averted.

DNA and RNA are what links us to our ancestors and the rest of the biological world. If managed ethically, genetics is biology and humanity’s last great hope for a sustainable biological world.

Oddly, when Gregor Mendel, dubbed father of genetics, undertook his work in the field of genetics, the word gene and the idea of genetics did not exist: for the simple reasons no-one had invented the word, nor associated the word with observations of species, inheritance, development, and the narrative arch of an organism’s life.

*Correction made 28th November.
The words making clear that each grandparent having a gene for blue eyes is the most likely explanation for the offspring of brown-eyed parents having blue eyes were removed as the sentence and paragraph were reworked during the editing process. Correction made within 36 hours and the words reinstated. HG.

Further reading.

(1) Genetics Of Colorectal Cancer. Accessed 27 November 2022.
(2) Aristotle's Biology. Stanford Encyclopedia of Philosophy. Accessed 27 November 2022
(3) A simplified explanation for jumping genes and their effect on the kernel color of Indian corn Accessed 27 November 2022

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