By Amy Tooke
2016 might be remembered for any number of reasons, but it also marks an anniversary of a major development in genetics. One hundred and fifty years ago, Gregor Mendel’s laws of inheritance were published. Mendel was an Austrian monk who painstakingly grew thousands of pea plants and counted the number of peas with certain characteristics. He came up with the concept of hereditary units that he named “factors” – or what we call genes today – and realised that there can be more than one version of each factor. Now, we call these versions of genes “alleles”. For example, a certain flower could have two alleles for colour, pink and blue.
By looking at the plants Mendel concluded that one copy of each factor is inherited from each parent. He outlined his ideas in his paper Versuche über Pflanzen-Hybriden (Experiments on Plant Hybridisation):
* The Law of Segregation
This law says that each parent contributes one allele when fertilisation takes place. Even though each parent will have two copies of a gene from their own parents, the alleles are “segregated” in the gametes (sex cells) so that there is only one copy per gamete. This means when the two gametes meet, there are two copies of each gene in the fertilised embryo.
* The Law of Dominance
If the two alleles are the same from each parent, the plant is “homozygous”, and will definitely show that trait, but if there are two different alleles (“heterozygous”), one version will be dominant and one will be recessive. The dominant allele will be the characteristic you see. So, if a plant inherits two pink colour alleles from its parents, it will have pink flowers. If the alleles it gets are one pink and one blue, and blue is dominant, it will have blue flowers.
* The Law of Independent Assortment
Leading on from the Law of Segregation, this law means that each pair of alleles is separated independently from the other pairs of alleles in the gametes – so you could have some alleles inherited from different grandparents in the gamete.
Mendel’s work didn’t have very much impact at the time; even Mendel didn’t realise its importance. The laws were rediscovered in 1900, and when combined with the idea that genetic information is stored in chromosomes in 1915, formed the basis of modern genetics. Where would we be today without the monk who grew some pea plants?