HELLO...GENETICS!

HELLO. You have passed the test of the universe. The very test of Life. Give yourself a pat on the back. Do a little jig around the room…or don’t. Cause you see, it’s not so much ‘you’ as much as ‘your atoms’.

From the sea of chaos formed after the dawn of Earth, you were (are?) a bunch of molecules whizzing around the Earth. And then, at about 3.5 billion years ago, a magical event took place. In Darwin’s ‘warm little pond’, the very first living organism breathed life. Through another biological miracle, the single organism mutated and reproduced, forming numerous other Ancient-Little-Living-Things ™¹. Years of painstakingly slow evolution, small changes to each set of beings, set the cycle of life in motion. Then, the Ediacaran and the famous Cambrian periods, where life expanded in relatively huge proportions, laid the foundation of complex, multicellular life ². Fast forward a few million years, and here you are!

A fossil of the Cambrian. A recognised form- the Trilobite. 

However, the intriguing bit is, we had a very faint idea as to what caused these mutations, this diversity in organisms, until the 1830s. 

WE start our journey from the fateful year of 1831. An ambitious young man returned home on the 29th of August to find himself an offer for an expedition requiring a naturalist to chart the coast of South America. Setting sail on the HMS Beagle, Charles Robert Darwin spent almost 5 years, doing everything- from geological surveys, discovering fossils to developing his famous evolutionary theory ³. On his voyages, he was convinced that despite the diversity, all humans were interrelated with a shared origin. Unlike his fellow scientists, he thought there was no unbridgeable gap between humans and animals. Darwin’s stroke of genius came with him conceiving his theory of ‘natural selection’. In a nutshell, it means that in the battle for life, survival and reproduction do not come down to pure chance, and that if the organism has traits that help it survive better, it may leave more offspring, and the traits would become more common through generations. Not to forget, his legendary book, ‘On the Origins of the Species’ generating quite a buzz in the community ⁴.   

ANOTHER pioneer is Gregor Johann Mendel, the brilliant German biologist who came up with stuff FUNDAMENTAL TO GENETICS. (Yes, I’m putting it in capitals, as there is no other way to convey how massively this has DEFINED biology.)  Between 1856 and 1865, Mendel performed experiments on Pisum Sativum (yep, scientific names. Commonly known as the pea) and traced inheritance patterns of certain traits. Mendel realised that the genotypes and phenotypes (oooh, big words. They mean the genetic material and physical traits of the organism respectively) of the offspring could be predicted and some traits were dominant over others. Mendelian inheritance became another pillar of biology. Darwin saw that all organisms are connected (I’m hoping for a reference to ‘The Lion King’?), whereas Mendel’s work explained how it could have happened. However, the significance of his findings was not fully recognised until the rediscovery of his laws, assuring in the modern age of genetics. 

The famous book.                                  Gregor Mendel. 

Before jumping into exciting times of the 1900s, we take a detour to explore the other aspects of the discovery of the wonder polymer, DNA.

From science class, we know that Deoxyribonucleic Acid is the fundamental building block to our genetic material. It carries the necessary information to make you, you. We also know that a bunch of processes are necessary for replication and translation, which helps execute the functions of the cell. To understand how DNA works, we need to understand what RNA is ⁵.Essentially, Ribonucleic acid is the precursor of DNA. The offspring (over a couple of hundreds of years) of those Ancient-Little-Living- Things™ had a primitive form of genetic material- RNA.

Coming back to our journey through the time machine, we reach 1869. Friedrich Miescher identified ‘nuclein’ (an early name for nucleic acids) by isolating a molecule from a WBC nucleus that would- surprise surprise! –later be called DNA. Picking up speed, in 1881, Nobel winner Albrecht Kossel – credited with naming DNA- isolated 5 nitrogen bases- Adenine (A), Thymine (T), Guanine (G), and Cytosine (C), and (T) replaced by Uracil (U) in RNA. 

Basic RNA structure. 

Now, Mendel’s theories were rediscovered. Unifications of Mendelian principles, proofs and experiments regulated to give key insights, flooded the scientific community. 

1902- Voilà! Mendel’s theories were finally associated with a human disease- Alkaptonuria- by Sir Archibald Garrod, beginning our quest for understanding of genetic disorders from errors in chemical pathways. A flurry of developments occurred soon after, which kick-started the bubbling new field.

An important mention is that of Thomas Hunt Morgan. In 1904, along with his team, he undertook a programme of fly (Yeah, you read that right, it’s those pesky little insects that hover over drains and food) breeding, each of them caught and studied, to see tiny changes in inheritance. By inducing mutations, they could link the particular characteristics and individual chromosomes, creating a somewhat primitive genetic map.

BY 1944, genetics was now in the rage. Oswald Avery saw DNA as the ‘transforming principle’ – that it’s DNA, not proteins that transform cell properties.  It’s quite easy to confuse the two. In simple terms, DNA is made of nucleotides- nitrogen bases- whereas proteins are made of amino acids, and carbon is one of the defining elements.

1944-1950: Erwin Chargaff discovers that DNA is responsible for heredity and varies between species. ‘Chargaff’s Rules’ an important concept, showed that in DNA, the amount of (A) must be equal to (T) and the amount of (G) must be equal to (C). This was an important postulate and also helped in the formation of the standard model of DNA. 

The Double Helix.

In the late 1940s, Barbara McClintock discovered the mobility of genes. Her discovery of the “jumping gene” won her the Nobel in Physiology. She hypothesised that gene regulation could explain how complex multicellular organisms made of cells with identical genomes have cells of different function. Identifying 2 dominant and interacting loci (fancy term for a point on the chromosome where the gene is located), Dissociation (Ds) and Activator (Ac), she found that (Ds) did not just cause the chromosome to break, it also had effects on neighbouring genes when (Ac) was also present, which also made certain stable mutations unstable. 

As discoveries picked up pace, the focus turned to resolving the structure of the mystery molecule. And this brings us to the famous Cavendish laboratory and King’s College, London. This concludes PARTIE-1 of our rendezvous with the discoveries that shaped modern genetics. 

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¹ The ™ is for fun and when used, I mean the queer life forms, which currently are unique to Earth.
² These periods had not been named or discovered till the 20th century and have been cited to provide clarity. However, Darwin’s ideas held good and the basic principle of evolution was known.
³ A tribute to the greats during this time who changed geology– James Hutton, Charles Lyell and many more. Darwin was particularly influenced by Lyell’s “The Principles of Geology”, and carried a copy with him on his voyage.
⁴ An important note- Alfred Wallace independently came up with the theory, which to Darwin’s shock, nearly replicated his own. (An interesting story lies here. However, for the lack of time, I would recommend Google-ing it out, as my summary may have not conveyed the exact amount of backstory.) When being presented to the Linnaean Society, it was presented as a summary of both ideas together. Wallace seemed pleased to have been included at all, and even referred to the theory for ever after as ‘Darwinism’. 
⁵ A detailed explanation will be addressed in future.