Introduction To Mendelian Genetics

Today we know that a person gets half of his genes from his mother and half of his genes from his father, but long time ago most people did not understand this apparently simple concept:

Hippocrates, also known as the father of medicine, about 400 years BCE tried to explain this phenomenon through what we now refer to as “pangenesis”. He suggested that the body produced a certain type of “seeds”, these seeds were then collected and transimetted to the offspring at the time of Conception. Of course he also thought that these seeds caused certain traits of the offspring to resembe those of the parents. This theory, also known as pangenesis as stated earlier, was then supported by Charles Darwin about 2000 years later and obviously ended up to be wrong.

Before mendelian genetics, some people accepted the ideas of Hippocrates and some people rejected them. After the invention of the microscope some people observed sperm thinking they could see a so called “homunculus” (little man), which was thought to be a miniature human waiting to develop within the womb of his mother. Scientists who believed this were known as spermists, thinking that the father was the only one responsible of his offspring. These people also thought that the resemblance between mother and offspring was due to external influences within the womb.

Of course after the spermists, came the ovists. These people thought that the egg was the only thing responsible for the offspring characteristics and that the role of sperm consisted only in “activating” the egg. Needless to say, both of these ideas were wrong.

Joseph Kölreuter, 1733-1806, was the first scientist to seriously study genetic crosses and he found out that in crossing different strains of tobacco plants, the offspring usually resembled both of its parents. His observations supported the so called “blending inheritance”, according to which hereditary traits could blend between each other. Of course this idea was wrong also.

Only thanks to the pioneering work of Gregor Mendel scientists will finally understand the way traits get inherited. This is what we now refer to as Mendelian genetics, or Mendelian inheritance, or Mendelism, or Monogenic inheritance. They all mean the same thing.