The 150th birthday of modern genetics is upon us! It's hard to sing happy birthday to an entire field, however, so here's a picture of the father of modern genetics in a birthday hat:
This piece of birthday perfection was made by multi-talented Curator, Natural Science Emma Burns
Tuesday 8 March marks the anniversary of Austrian monk Gregor Johann Mendel's presentation on hereditary pea traits.
Then, on Tuesday, Professor Roger P. Hellens is giving a talk on Mendel and his legacy on Tuesday 8 March at 6.30pm – check it out here.
Peas and punnet squares
The gutting thing about poor old Mendel is that his work was largely ignored during his lifetime. It wasn’t until it was revisited in the early 1900s (a few decades after his death) that people realised the magnitude of his findings.
Do you remember drawing punnet squares in high school biology about wrinkly peas and brown and blue eyes? You've got Mendel to thank for that!
He began experimenting in 1856. Using the humble pea plant, he sought to understand how traits passed from parents to their offspring. His work, finally published in 1866, gave rise to a new and exciting field of science that underpins the evidence for evolution by descent.
So in a way, it is also happy birthday to the field of genetics, even though Mendel wouldn't have known that term.
Prior to Mendel playing with peas, biologists believed that the traits observed in offspring were the result of blended inheritance. So, they thought the traits from mum and traits from dad combined and averaged out to create the offspring’s trait. A tall parent plus a short parent produced offspring at a height in the middle, for example.
But this wasn’t the case.
Mendel spent eight years breeding generation after generation of pea plants. He cross bred parent plants with specific observable traits (phenotypes) that were visibly different, such as the flower colour, the seed colour, the pod shape and more.
This long period of time, with a test subject that reproduced quickly, made his research elegant and convincing in comparison to other early breeding studies.
Mendel recorded which of the two traits were expressed in the first generation offspring. He then allowed the pea plants to self-pollinate and recorded how many times each trait popped up in subsequent generations.
For example, when cross breeding yellow pea-producing peas with green pea-producing peas, he observed that the first generation of offspring produced yellow peas exclusively.
Drawing of pea traits diagram courtesy of Emma Burns and Assistant Curator, Natural Science Ellen Sima
When he isolated this first generation offspring and allowed them to self-fertilize, Mendel found that that the second generation offspring mostly bore yellow seeds, but a small number bore green seeds. This meant that a yellow seed plant had produced a green-seed offspring!
There was no average between the two colours (like a yellowy-green seed) or pods containing a mixture of yellow and green seeds. If he’d found either of those things, it would have made a case to support the blended inheritance theory.
Mendel made some important conclusions from these experiments:
- Inheritance of a trait is determined by a “unit” that is passed from parent to offspring (today we call these genes!).
- Offspring inherit one unit from each parent for each trait.
- Some units are dominant over others. When there are two traits and one is dominant, the other is recessive. The recessive trait will not ‘show up’ in the plant, but can be passed along to its offspring.
- If a plant had both a yellow pea unit and a green pea unit, it would bear yellow peas. This is because the yellow pea trait is dominant.
- In some combinations, two of the same units will be passed to the offspring. Two dominant yellow pea units will make a yellow plant, and two recessive green pea traits will make a green plant.
- It’s only when a plant gets two recessive green pea units that it will grow green peas.
- A trait may not show up in an individual, but can still be passed on to the next generation.
- So, just because a pea is yellow doesn’t mean it can’t pass on the potential for greenness to its offspring.
Moving past Mendel
Since Mendel's research, contemporary geneticists have discovered oodles more about genes and how they are expressed in organisms. While Mendel’s findings still provide good basic principles, we now know that there is way more going on.
Thanks to the discovery of DNA – the building blocks of genes – whole genomes have been mapped and published for different species. It reinforces that all life on Earth is related. For example...
...geneticists have discovered that humans share 50% of our DNA with bananas! To learn about your banana cousins and about the field of genetics, head up to the Animal Attic on Sunday 6 March to do some genetic sequencing on bananas, guided by the capable hands of Genetics Otago.
Happy Birthday Mendel, and rest in peas.