Gregor Mendel

The Father of Genetics

Gregor Mendel is widely considered to be the father of genetics. But how could an Austrian monk be the founder of the study of heredity? Keep reading to find out how Mendel could shape modern science with just a garden of pea plants.

Gregor Mendel lived from 1822 to 1884. He developed many theories for how traits are passed on from parents to their offspring. He used pea plants to test his theories because a relatively large number of seeds are produced by each plant, they area easily cross-pollinated, and they have many contrasting traits in their phenotype that Gregor could understand and study. Mendel’s experiments focused on how a specific trait was passed down through families.

Gregor’s first experiment was to cross-pollinate two tall pea plants (classified with genotype TT). Mendel noticed that in that generation, there were only plants that were tall, with genotype TT. He concluded that there is a factor for tallness that is passed down. He then cross-pollinated two short pea plants (classified as genotype tt). He noticed that in the "short" generation, there were only genotype tt plants produced. After the two experiments, Mendel concluded that there is some factor for height that can be passed down through generations (in pea plants). Gregor Mendel’s next experiment led to lots of advancements in heredity after the turn of the century. He cross-pollinated two plants with genotypes TT and tt. The result was a tall plant with genotype Tt. When he bred two of those Tt plants, the result was that three-fourths of the generations were tall plants and one fourth was short plants. Gregor Mendel had discovered that the short trait disappeared for a generation, and then reappeared in the second generation.

Mendel made correct observations and assumptions that weren’t appreciated by other scientists for many years. He deduced that there were two of each factor for traits, because they disappeared and reappeared in the next generation. He deduced that there were two types of these "factors": dominant and recessive. The dominant factors are the ones that appear in the phenotype whenever they are paired with anything else. Recessive factors are the ones that are hidden when paired with dominant factors, and only appear if you have two of them. In Mendel’s experiments with pea plants, the t factor (which has now been replaced with the word allele) is recessive, and the T allele is dominant. Today, capital letters are the dominant alleles (like T), and lower-case letters are recessive traits (like t). Mendel’s theory about genes had a few restrictions, because there can be codominance, incomplete dominance, and multiple alleles (see Heredity Basics/Dominance).

Gregor’s observations are now called "Mendel’s Laws." The first ‘law’ that Gregor formed was the Law of Segregation. This rule states that since gametes (sex cells) only have one full set of chromosomes and not two, during the process of forming these gametes, the two sets of chromosomes are separated. Mendel’s second law of genetics is called The Law of Independent Assortment. This law says that alleles (one possible form of a gene) for one trait separate and segregate independently of other alleles for different traits. Basically, this means that one allele that you receive from your parents takes form in your phenotype completely uninfluenced by alleles that are for different parts of your phenotype.

The thing you have to remember here is that Gregor Mendel figured out everything you just read in the 1850’s. Mendel didn’t have the help of modern science to figure out about recessive and dominant factors. Though he didn’t figure out exactly what those "factors" are, Gregor was ultimately proven to be correct. People think that genetics is a relatively new science, but, incredibly, Mendel did exactly what we are doing today 250 years ago, but, he did it with pea plants!

Mendel
Morgan
Griffith
Hershey and Chase
Watson and Crick