University years

How did Mendel discover inheritance?

I began my Biotechnology course at the university of Pavia in October 2010. I just turned 19 and luckily the first semester of this course started somehow smoothly. Since in Italy there is a great discrepancy between high schools, universities tend to use the first semester of the first year of each course to put all the students on the same page. Therefore, the first classes I was attending were all basic courses: math analysis, inorganic chemistry, the biology of the cell and so on. I guess the most interesting class I had to attend that first year was the inorganic chemistry practical laboratory: finally, I was starting to wear a lab coat and do “experiments”. I had so much fun in learning how to pH a solution, to create a salt and more in general “playing” around in the lab. I was feeling comfortable handling pipettes and glassware; I was super careful following safety rules and I was trying to calculate and measure everything up to an almost annoying precision. I had a blast finally seeing and touching with my own hands everything I had only seen and studied on books.

Inorganic chemistry was one of the big exams of that semester and everything we did in that course was basically all the chemistry I studied in high school. When I took the exam, I got an excellent grade and the head of that course even offered me to move to a Chemistry bachelor. However, as you can all imagine, I was very much convinced of my choice and even though I thought about this opportunity a bit, I thanked him and refused his offer. Although I was not yet immersed in the proper “biological” classes, I knew that was what I wanted to do.

Anyway, the first biological and finally new class I had during my first university year was the basic genetic course. It was covering quite a lot of different themes: from Mendel to genetic mutations, from RNA to genetic diseases and up to biotechnological tools for nucleic acids. It felt like finally I was studying what I have always wanted to learn.

However, I will talk about the more interesting courses I had during my Bachelor in the next few posts and for now, for the SRF, I will talk a bit about Mendel, the monk who is considered the father of Genetics.

“Science Related Fact” (SRF):

Gregor Mendel (1822-1884), the man considered the father of Genetics, was a monk in the Brno monastery, in Moravia. He discovered the fundamental laws of inheritance through his work on pea plants: Mendel realised that each inherited trait is defined by a gene pair; parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair; the offspring inherits one genetic allele from each parent when sex cells unite in fertilisation.

Mendel was focusing on individual traits of the pea plant so that he could readily follow them in the offspring. Since pea plants are naturally self-fertilising, “pure-bred” strains were readily available. Each strain contained only one form of the gene that determined a trait. For example, the colour of the pea plant flowers can be purple or white. Pure-bred plants with purple flowers only produced offspring with purple flowers. Pure-bred plants with white flowers only produced offspring with white flowers. From the results of further experiments, Mendel reasoned that pure-bred plants must have two copies of the same gene for each trait (see picture below).

In a cross between two pure-bred parents with different traits like the colour of the flowers, the hybrid offspring would have both the gene for purple and white flowers. However, Mendel proposed that although both genes are present, there is no blending of colour because the gene for purple is “dominant” over the gene for white. The dominant trait is seen whenever a single copy of its gene is inherited. When he crossed the hybrid offspring, white flowers reappeared in the next generation. Mendel reasoned that the “recessive” green trait is shown only when a copy of the recessive gene form is inherited from each parent (see picture below).

Pure bred parental plants cross fertilisation leads to a first generation of offspring (F1) showing only the dominant character gene. However, the recessive trait can reappear in a ratio of 3:1 in the second generation (F2), by crossing the hybrid offspring. From pinterest.com

Therefore, he tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. Mendel was able to recognise the mathematical patterns of inheritance from one generation to the next. This genetic experiments with pea plants took Mendel eight years and he published his results in 1865. Unfortunately, Mendel’s work was not appreciated until 1900, after the discovery of chromosomes and modern genetics.

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