Johann Gregor Mendel Biography

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World of Genetics on Johann Gregor Mendel

The science of genetics can trace its origins to biologist Gregor Mendel. In meticulous studies with pea plants, Mendel acquired the experimental data necessary to formulate the laws of heredity.

Born in Heinzendorf, Austria (now the Czech Republic), Mendel was the son of a peasant farmer and the grandson of a gardener. As a child, Mendel benefited from the progressive education provided by the local vicar, and he eventually enrolled at the Philosophical Institute in Olmutz (now Olomouc). However, Mendel's worsening financial condition repeatedly forced him to suspend his studies, and in 1843, he entered the Augustinian monastery at Brünn (now Brno).

Although Mendel felt no personal vocation at the time, he believed that the monastery would provide him the best opportunity to pursue his education without the financial worries. He took the name Gregor and eventually was placed in charge of the monastery's experimental garden. In 1847, he was ordained as a priest. Four years later, he was sent to the University of Vienna to study zoology, botany, chemistry, and physics. Following his studies, he returned in 1854 to the monastery and also began teaching the natural sciences at the Brno Technical School.

From then until 1868, in his limited spare time, Mendel performed most of his now-famous heredity experiments. No one had yet been able to make any statistical analysis in breeding experiments, but Mendel's strong background in the natural sciences and his coursework in principles of combinatorial operations prompted him to try. Mendel worked mostly with pea plants, carefully selecting pure varieties that had been cultivated for several years under strictly controlled conditions. He crossed different plants until he produced seven easily distinguishable seed and plant variations (yellow vs. green seeds, wrinkled vs. smooth seeds, tall vs. short plant stems, etc.).

Mendel discovered that, while short plants produced only short offspring, tall plants produced both tall and short offspring. Since only about one-third of the tall plants produced other tall plants, Mendel concluded that there must be two types of tall plants: those that bred true and those that did not.

Mendel continued experimenting, attempting to find intermediate varieties of the offspring by crossing these different plants. In other words, if a tall plant was crossed with a short plant, Mendel expected the result would be a medium-sized plant. Mendel soon found that this was not the case. Mendel crossed short plants with tall plants, planted the seeds from that union, then self-pollinated the plants from this second generation. He followed the results by counting and recording each generation. All of the offspring that sprouted from the short-tall cross were tall, but the offspring from the self-pollination of those tall plants gave him half tall plants (non-pure), one-quarter pure tall, and one-quarter pure short. Tallness, the more powerful characteristic (the one that shows up the most), was dubbed the dominant trait. Shortness, the weaker characteristic (the one that is frequently masked), was called therecessive trait. It did not seem to matter whether Mendel used male or female plants, the results were always the same. Mendel's quiet, methodical investigation took over eight years to complete and involved more than 30,000 plants.

The results of Mendel's initial plant breeding experiments formed the basis of his first law of heredity: the law of segregation. This law states that hereditary units (genes) are always in pairs, that genes in a pair separate during division of a cell (the sperm and egg each receive one member of the pair), and that each gene in a pair will be present in half the sperm or eggs.

Mendel's further experiments established a second law: the law of independent assortment. is law states that each pair of genes is inherited independently of all other pairs. However, it holds true only if the characteristics are located on different chromosomes. By sheer coincidence, Mendel had indeed selected such characteristics. But genes located on the same chromosome, as was Hunt Morgan later discovered, are usually inherited together.

In all, Mendel uncovered the following basic laws of heredity: 1) heredity factors must exist; 2) two factors exist for each characteristic; 3) at the time of sex cell formation, heredity factors of a pair separate equally into the gametes (the sperm or the egg); 4) gametes bear only one factor for each characteristic; 5) gametes join randomly no matter what factors they carry;6) different hereditary factors sort independently when gametes are formed.

Mendel, however, never received acknowledgment during his lifetime for the important contribution he had made to the study of heredity. Although Mendel carefully documented his experiments, presented his findings to the Brünn Society for the Study of Natural Science in 1865, and published Experiments with Plant Hybrids the following year, the scientific community was indifferent. Botanists, including Karl Wilhelm von Nägeli,to whom Mendel sent his work, were unaccustomed to statistical analysis. Also, scientists as a whole were hesitant to give credence to such novel theories regarding heredity from such an obscure man.

Mendel died in Brünn on January 6, 1884. Ironically, because of Mendel's refutation of the intermediacy theory that he himself had once posited, Charles Darwin's evolutionary theory was greatly bolstered, for prior to Mendel natural selection was believed to be counteracted or compromised by repeated blending of gene characteristics throughout the hereditary cycle. Not until 1900, when Mendel's pioneering work was rediscovered by Hugo de Vries and others, did Mendel begin to receive scientific recognition.