Mendelian genetics is a theory of genetic inheritance which was developed by Gregor Mendel in the 1800s. It is widely regarded as the cornerstone of classical genetics, and while Mendel didn't get everything quite right, he got very close. Students in science classes are introduced to the concept of Mendelian genetics at a very early age, to prepare them for more complex discussions about genetics.
At the time that Mendel was working, not very much was known about genetics. Mendel came up with an idea which was innovative for the time: creating a pure genetic line for research and recording his results meticulously. He chose peas for his experiments, since they grow quickly and are easy to hybridize, and along the way he made a number of notable discoveries, formulating two laws of genetics which weren't very popular with the scientific community of the time.
Mendel's first law was the Law of Segregation, which dictated that each organism inherited half of its genetic material from one parent, and half from the other. The second was the Law of Independent Assortment, which stated that traits manifested independently from each other, and that traits could be divided into dominant and recessive categories. What Mendel didn't realize is that some genetic traits actually involve multiple locations which interact with each other, like eye color, and some traits actually are linked, like hemophilia, which is a sex-linked trait that only appears in people who inherit a Y chromosome.
Although Mendel's conclusions were not totally perfect, the concept of Mendelian genetics still astounded the scientific community. His theory explained why traits can remain hidden for generations, which ran against popular theories which suggested that traits were inherited continuously. The idea of inheriting genetic material equally from both parents was laughed at, thanks to the fact that microscopes were not advanced enough to detect the process of meiosis.
At the time that Mendel's theories were published, they attracted little attention. In the early 20th century, several scientists referenced his work, building upon the basic concepts of Mendelian genetics and adding their own concepts and ideas to create the theory of classical genetics. Although Mendel did not live to see his theories vindicated, he would undoubtedly take some comfort from the fact that he is thought of as the father of genetics. In honor of Gregor Mendel, traits which are determined by genes at a single location are known as “Mendelian traits.”