8 February 2015 marked 150 years since the first of Mendel’s lectures where he presented his results on pea breeding for the first time. These lectures, based on his paper Versuche über Pflanzen-Hybriden (Experiments on Plant Hybridisation), presented the world with a vision of genetics never seen before – and led to him gaining the title ‘The Father of Modern Genetics’.
Mendel’s work is world-famous, and his historical experiments are used to teach heredity in schools across the globe. Mendel, a monk working in the gardens of his monastery, studied seven plant traits to study how they were inherited by their offspring: flower colour, flower position, plant height, seed texture, seed colour, pea pod texture and pea pod colour.
These studies led to the theory that one trait would be dominant over a recessive other – and the offspring’s traits would be presented in a 3:1 ratio. Before this, the prevailing theory was that traits blended together – so a red flower and a yellow flower would give rise to an orange one.
At the time of the presentation, however, Mendel’s work was largely ignored and forgotten until it was rediscovered 35 years later – sadly after Mendel’s death. During this time, Darwin was putting together his theories, entirely unaware of Mendel’s work, and many think that the field of genetics would have been established far earlier, had this not been the case.
One of the biggest advocates of Mendel’s work was William Bateson, who coined the word ‘genetics’ (incidentally, he was also director of the John Innes Centre during the early 20th century). Once accepted, Mendel’s work was quickly deemed revolutionary and taken up by plant breeders to be used as the foundations for the complicated genetics and biotechnology used today.
Mendel’s work also encountered sceptics (as much scientific work does). Statisticians claimed that Mendel’s results were ‘too good to be true’. There were even accusations that Mendel may have fabricated his results, or that he selectively represented his best experiments.
Nowadays, the system of peer-reviewed journals would catch these criticisms early, and scientists could repeat experiments or do more to show this wasn’t the case. But the delay in recognition of Mendel’s work meant he wasn’t around to defend himself. Despite these criticisms, his work is still accepted by the scientific community – and the work has been repeated plenty of times since these claims were made.
Understanding Mendelian genetics isn’t the end of the story for understanding inheritance. Mendel’s work easily explains inheritance where one gene is involved. But many of our traits are caused by multiple genes – and so the ratios become a little more complicated than 3:1. We often need to understand how different genes are expressed and how they interact to understand how a trait is expressed.
Several other mechanisms may also play a role in how traits are passed on – this is called ‘non-Mendelian inheritance’. It includes extra-nuclear inheritance, such as inheritance through mitochondrial or chloroplast DNA. These are separate from the nuclear DNA carrying the traits Mendel looked at.
Our mitochondria come from our mother’s egg cell, and so all of the genes found in our mitochondrial DNA are maternally inherited. Mutations in mitochondrial DNA can lead to devastating mitochondrial diseases – currently the subject of a lot of press coverage as MPs recently voted to allow IVF treatment using a donor’s mitochondria.
Another type of non-Mendelian inheritance is caused by recombination, a process by which DNA from one helix is copied into another DNA helix. This can alter the sequence of genes and the nature of the traits they express.
Understanding the many different forms of inheritance combined with Mendel’s original discoveries will enable new breakthroughs in both medicine and plant science – as we strive to cure heritable diseases and improve our crops to help with growing concerns of food security.
Understanding inheritance opened the door to the field of genetics, not just in plants, but also in human disease. It is incredible to think how much knowledge has followed the work of a monk who was curious about the colour of his sweet peas.
It took Mendel eight years and over 10,000 plants to reach his conclusions. Hopefully, we early career researchers can take comfort in this: perhaps those seemingly endless experiments or huge screens might lead to that one groundbreaking discovery. We might even see our work immortalised, like Mendel’s, in a Google Doodle …
Izzy is a John Innes Centre PhD student. She tweets as @isabelwebb.