Asking Questions in Biology

Background Knowledge & Content

Gregor Mendel

Johann Gregor Mendel was born in Heinzendorf bei Odrau, near the Moravian-Silesian border in what is now the Czech Republic (then part of the Austrian Empire).¹ He was born on July 20, 1822, to a farming family in the northern part of Germany. By age eleven, his school master was impressed with Gregor's unusual intelligence and learning ability and recommended sending him to a school that required extra expenses. Despite the expenses for his family, Johann graduated with honors.

Gregor continued his studies despite his father’s request to return home. He went on to the University of Olmutz, enrolled in the philosophical institute, and studied practical and theoretical philosophy. He excelled in physics and math and graduated with high honors. While at university, Mendel met Johann Nestler, a notable biologist. Nestler was interested in heredity research with animals and plants, which influenced young Mendel.

At age twenty-two, Gregor decided to become a monk and joined the Augustinian order at the Saint Thomas Monastery. While studying theology, Gregor also had access to other subjects in the monastery libraries, such as music, philosophy, math, and botany. He had access to a vast literature to advance his education. Heredity and the traits of animals and plants played an important role in his studies, and the monastery’s head friars and abbots shared his interest.

Gregor continued his studies amid financial difficulties and health issues, yet he excelled in school with high marks. He settled for an uncertified teaching job and was unable to complete a certified teaching exam because of stress and other illnesses. Gregor kept himself busy and continued with meteorology recordings, astronomy observations, caring for the fruit orchard, beekeeping, growing other flowers, and his pea experiments.

He had originally begun to study mice, but the head Abbot told him it was improper to watch mice mate and produce offspring. The Abbott stated mice were unclean and unorthodox for the monastery. Instead, Mendel deliberately chose the genus Pisum because it met his three basic requirements for experimental plants (simplified): consistent characters across generations (true breeding), protection from foreign pollen during flowering, and undisturbed fertility of hybrids and offspring.² Based on Mendel’s own words, he was interested in proving that characters slowly changed over time, which supported Darwin’s concept of transmutation of species.

He tested thirty-four varieties and carefully chose observable characters such as flowers, seeds, stems, and pods. Planting them in small beds and pots provided an environmentally controlled setting that revealed observable traits. Soil and air temperature, germination time, and light affected variations in certain plant characteristics. Mendel selected completely dominant unit-characters to study not only because they could readily be visually discriminated (from the recessive forms) but also because they were easy to symbolize, hence denote.³ When he discovered that flowers and seeds showed consistent association, he did not express them in his presentations. He explained that his plant experiments were controlled and intentionally carried out to show how hybrid offspring were arranged into separate generations and relationships.

Using capital letter ‘A’ and lowercase ‘a’ helped Mendel keep track of dominant and recessive alleles, respectively, when alleles are paired together in the genetics of diploid organisms. Mendel used this method to catalog his experimental results quickly. As his experiment expanded with more offspring populations, he used numbers with letters and solid and dotted lines to identify groupings or differentiating characters in the hybrid.

Mendel wrote letters to Nageli (a prominent Swiss botanist), explaining that it was difficult to find suitable plants for an extensive experiment. Nageli suggested that it may support his pea plant research. Gregor spent a good portion of the rest of his life retrying his experiment with other species like hawkweed and dandelions, which are nearly impossible to control in terms of pollination, a project he later abandoned to focus on becoming an abbot until his death.⁴ It was a failure because Gregor did not know the plant produced asexually (known as apomixis) and did not produce predictable traits.

Although his research was not openly accepted during his lifetime, his work became famous after the twentieth century, and today he is known as the father of genetics. Words like hybridization, characters, heredity, cross-pollination, traits (alleles), dominant and recessive, and the law of segregation became common vocabulary in biological science.

Recessive and dominant traits

Understanding the basis of heredity was challenging for Mendel as he researched crossbreeding peas in his garden in the mid-1800s. He made key decisions that helped his work succeed. He focused on traits that were more prominent than others not seen. For example, smooth or wrinkled peas when crossbreeding. He noticed traits disappearing, then reappearing in later offspring. Mendel defined: “those characters which are transmitted entire, or almost unchanged in the hybridization, and therefore in themselves constitute the characters of the hybrid, are termed dominant, and those which become latent in the process recessive.”⁵ Mendel specified that hybrids generate two different germ cells. These germ cells contain elements of different organelles, and when some unite, they form a new embryo. The embryo forms a joint union to become a germ cell. Mendel did not know or discuss the physical basis of this observation, which he described as A+2Aa+a rather than the polynomial AA+2Aa+aa. He depicted the organelle's separation within germ cells.⁶ Mendel’s research created a foundation of genetic traits and heredity, which became widely known when his research was rediscovered. His terms dominant and recessive traits show that traits from both parents characterize hybrid offspring.