The Elements of Evolution (32-4) Gregor Mendel

 Gregor Mendel

The value and utility of any experiment are determined by the fitness of the material to the purpose for which it is used. ~ Gregor Mendel

Gregor Mendel (1822–1884) was an Austrian monk who made the most of his life through patience and diligence. His chosen occupation and precise nature would delay appreciation of his work until long after he died.

Mendel came from a family of peasant farmers. His parish priest and teacher, impressed with Mendel’s intelligence in elementary school, helped him get secondary schooling; unusual for a peasant.

Mendel struggled for funds. One of his professors suggested joining the Augustinians, whose main work was teaching, and who would pay for Mendel’s schooling. Mendel became a monk at 21.

The abbey was a remarkable place: access to scientific instruments, an extensive library, and an excellent botanical collection. The abbot shared with Mendel a love of plants.

Thanks to his mentorship, Mendel was able to study at the University of Vienna from 1851 to 1853. He was sent to Vienna partly because Mendel had failed his teaching examination.

Mendel took courses in plant physiology and experimental physics. His professors emphasized studying Nature via experiments, underpinned by mathematical models. While Mendel had enthusiasm for his studies, upon his return from Vienna, he again failed his teaching exam.

This limited Mendel to substitute teaching. On the bright side, it also let him spend more time doing what he loved: gardening.

Between 1856 and 1863, in the monastery’s garden, Mendel cultivated and examined 29,000 pea plants, tediously chronicling his observations about their flowers (color and position), seeds (color and shape), pods (color and shape), and height. The variety of their easily identifiable traits, quick generation, and copious offspring made peas a fortuitous choice.

Mendel detailed laws of genetic heredity in Experiments on Plant Hybridization, published in a regional natural science journal in 1866. Given its title, Mendel’s paper was understood as being about hybridization, not heredity, and had negligible impact for over 3 decades, until it was rediscovered.

Mendel hypothesized hereditary units, how inheritance manifested, about hybridization, and expression of dominant or recessive characteristics. Mendel’s heredity laws were: 1) the law of segregation, and 2) the law of independent assortment.

While genes are paired in normal cells, they are segregated in sex cells (eggs or sperm), which unite to form a gene pair. The pair express either a dominant or recessive trait.

A dominant gene trumps a recessive gene, so it takes 2 recessive genes for a recessive trait to be expressed; whence Mendel’s law of segregation.

Mendel’s law of segregation is nominal and subject to violation. Plants are known to sometimes employ ancestral alleles, not parental genes. This paramutation may occur by inheritance via double-stranded RNA, not DNA.

Mendel’s 2nd law, independent assortment, was that the expression of any 1 genetic trait is not influenced by another. It may have seemed that way for pea plants at first blush, but inheritance is more intricate than that. Most genes are linked. For example, biorhythms determined by an organism’s circadian clock are the product of a gene complex.

Many processes are under biorhythmic sway, from organs to tissues to cells. Even the production of ATP in mitochondria oscillates by a molecular clock.

Done with peas, Mendel turned to honeybees, creating a hybrid strain so vicious they were destroyed. His work was inconclusive as to heredity in mating bees.

Perhaps Mendel would have had better luck if he had chosen fruit flies, the genetics of which were first studied by American evolutionary biologist Thomas Morgan at the turn of the 20th century. Morgan followed in Mendel’s footsteps, though he was initially skeptical of Mendel’s laws of heredity.

Fruit flies (particularly Drosophila melanogaster) would go on to be geneticists’ favorite victim, even though they fail to exhibit some important genetic mechanisms found in other animals. While helpful for learning the fundamentals, the rather exclusive focus on fruit flies by researchers retarded for decades a more thorough understanding of genetics, especially epigenetics.

Mendel was promoted to abbot in 1868. His increased administrative responsibilities, especially a fight over taxes with the local government, spelled an end to his scientific work.