What is Mendelian Genetics?

Mary McMahon
Mary McMahon

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.

Gregor Mendel studied pea pods as a way to research genetics.
Gregor Mendel studied pea pods as a way to research 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.

Gregor Mendel uncovered the basis for our understanding of how traits, such as hair and eye color, are passed on.
Gregor Mendel uncovered the basis for our understanding of how traits, such as hair and eye color, are passed on.

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.

Each individual receives a combination of genes equally from the biological father and the biological mother.
Each individual receives a combination of genes equally from the biological father and the biological mother.

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.

Gregor Mendel is known for his work on genetics and heredity.
Gregor Mendel is known for his work on genetics and heredity.

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.”

Someone who has two copies of a recessive trait, such as blue eyes, will express that trait.
Someone who has two copies of a recessive trait, such as blue eyes, will express that trait.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

nextcorrea

@SZapper - You are right he probably was disappointed. But it is my understanding that mendel was a monk and that his early genetic experiments came out of a fascination of the natural world that he believed to be an act of creation. So perhaps he was motivated by a higher cause than most scientists. I would like to think that he worried about larger things than respect from the scientific community. But who knows what was going on inside Mendel's head. He was obviously a complicated guy.

SZapper

@indemnifyme - I have vivid memories of filling out those Punnett squares too. I'm pretty sure they are in fact based on Medel's theories.

When I took biology I did find Mendelian genetics to be interesting. However I always focused more on the "human interest" piece of it: the fact that no one believed Mendel's theories during his lifetime. I always felt a little sorry for the poor guy, especially because he was right!

indemnifyme

I remember learning about Mendel and his experiments with the peas when I was in middle school. I also remember filling out about a million Punnett squares, which I believe are based on the Medelian theories.

I was really disappointed when I took high school biology though because some of the traits we did the squares for aren't as simple as they seemed. For instance, as mentioned in the article, eye color is decided at more than one location. However I recognize that Medel's work probably provided the basis for modern genetics.

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