Mendelian Genetics

You may hear about DNA in the news or in conversations. But what is DNA, really?

Gregor Mendel was born in Austria in July 1822. Gregor and his two sisters grew up on a farm, growing various plants and caring for bees. As an adult, he studied at the University of Olomouc in what is now the Czech Republic.

Because of financial difficulties paying for his education, he became a friar. He entered St Thomas's Abbey in Brno and trained as a priest. He started much of his research into genetics while he was at St. Thomas’s Abbey.

Mendel’s Research

Mendel experimented with pea plants while he was at the abbey. His research focused on the inheritance of pea plant traits. After a few initial experiments, he decided to study seven different traits that seemed to be independent of each other.

The 7 traits

Note: For the purposes of this blog post, we’ll focus on one of these traits: seed color. It’s easy to understand, and fits the principles that Mendel established.

Mendel kept breeding his pea plants until he could get “pure-breeding” varieties. Some of these pure-breeding plants would only ever produce yellow seeds. Some of these pure-breeding plants would only ever produce green seeds. These became his “Parental” or “P” generation.

He then crossed the yellow pure-breeding plants with the green pure-breeding plants. This produced the first filial generation, or “F1” generation. All of the resulting F1 generation had yellow seeds. There were no green seeds.

He then crossed the F1 plants with each other. The new generation was named the second filial generation, or “F2” generation. This new generation was unusual: green peas reappeared in some of the plants. The other strange thing was that there was a specific ratio of yellow peas to green peas. That ratio was 3 yellow pea plants: 1 green pea plant.

This happened in every set of traits that Mendel tested. The F1 generation would only ever show one trait. The F2 generation would see the “hidden” trait reappear in the same ratio of 3:1. He repeated these crossbreeds many times, and would end up with similar results. Based on his results, he formulated three rules that the plants were following:

1. Law of Segregation

In order to breed the pea plants, Mendel would pollinate female flowers with male pollen. He hypothesized that both parents transmitted information into their offspring, and that information was chosen at random from each parent.

Every person has two sets of genes that they get from their parents. Each parent donates 1 set of genes. The alleles for these genes are selected randomly. This is Mendel’s first law: The Law of Segregation.

2. Law of Independent Assortment

Mendel’s second law, the Law of Independent Assortment, logically follows from the first. While the first law states that the alleles separate independently of one another, the second law states that the genes for different traits separate independently of each other too.

3. Law of Dominance

Based on how some traits would disappear, or “recede,” Mendel’s derived his third law: The Law of Dominance. This law states that some alleles will “dominate” other alleles, forcing them to recede. Appropriately, alleles that recede are called recessive and the alleles that dominate are called dominant.

Reception by the Scientific Community

Mendel’s work was the first formal scientific inquiry into the nature of inheritance, or how traits are passed down. When Mendel published his work, however, he was largely ignored. Some scientists dismissed his work, and it never received the attention it deserved. Mendel lived at the same time as Charles Darwin, but Darwin was not aware of his work. Had Darwin been aware, he likely would have incorporated Mendel’s work into On the Origin of Species.

It wasn’t until 16 years after Mendel died in 1884 that his work would gain the attention it deserved. In the spring of 1900, three separate scientists came to the same conclusions that Mendel did, through experiments of their own. Each of them credited Mendel for their work, and soon Mendel’s work was republished.

Mendelian Genetics Today

Modern biologists hold Mendel’s work in high regard. His work established the cornerstones upon which modern genetics are based.

However, much like any scientific field, Mendel’s work was very limited. Most genes that we know of today do not follow Mendel’s laws. In fact, genes that follow Mendel’s laws are relatively rare. Most genes affect other genes, are inherited together, and don’t always separate randomly. Nonetheless, without the basic work that Mendel started, we would be worse-off today.


Want more stuff like this?

About Us

CRI Genetics is an advanced team of Geneticists, Anthropologists, and Social Scientists, who work together to deliver you the most accurate estimation of your ancestry possible.