Gregor Johann Mendel  *1822 - †1884

 

J.G. Mendel during his teaching years in Brno - a photo from 1862

Basic biographical data

He was born on 20 July 1822 in a peasant family in the village of Hynčice in Moravia (Fig. 2), which is now part of the village of Vražná (Nový Jičín district). His native language was German.

After attending an elementary school in Hynčice and a grammar school in Opava, he enrolled at the Institute of Philosophy at the University of Olomouc in 1840. In 1843, he was admitted to the Augustinian monastery of St. Thomas in the Brno district of Old Brno as a novice. He adopted the name Gregor. The Brno Augustinian monks were renowned scholars who actively participated both in university and grammar school education throughout the Austro-Hungarianentire Empire. At that time, they held a position of significance in the scientific and cultural life of Moravia.

Having accomplished his theological studies in 1848, he started to attend professor Diebla's lectures on agriculture at the Institute of Philosophy in Brno. In 1853, he successfully finished his two-year studies at the University of Vienna.

In 1856, Mendel commenced his experiments with crossbreading plants, namely the pea plant, and, in 1862, he began meteorological monitoring for the Institute of Meteorology in Vienna. He conducted his meteorological monitoring  with exceptional accuracy and continued to do so almost until his death in 1884.

In 1863, Mendel completed his crossbreading experiments with the pea plant (Pisum) and on 8 February 1865 at the Society for Natural Science meeting in Brno, nine years after Darwin published his book "On the Origin of Species", he presented the first part of his theory on the transfer of hereditary traits. The second part of his classic work followed on 8 March. In 1866, his short monograph, "Experiments with Plant Hybrids" (Versuche über Pflanzen-Hybriden), was published.

In 1868, he was appointed abbot and prelate of the Augustinian monastery in Brno.

A year later he received his only recognition during his lifetime in  natural science circles - he was elected vice-president of the Society for Natural Science in Brno. On 9 June 1869 he presented to the members of the Society the outcomes of his second remarkable collection of experiments concerning crossbreeding hawkweed (Hieracium-Bastarde). In the same year he became a member of the Beekeeping Association in Brno.

In 1883, Mendel fell seriously ill and on 9 January 1884 he died at the  monastery. He was buried in an Augustinian tomb at the Central Cemetery in Brno. The requiem in the church was conducted by the later world-famous Czech composer Leoš Janáček.

Mendel's research activities

Mendel believed the variability of species to be a proven fact. He made a remarkable diagnostic changeover when he refused to assess an organism as a whole, but considered the organism's individual traits. He understood the individual traits of an organism, e.g. the shape of a mature seed, contrapositively, i.e. one seed round and second one angular were for him as two sides of one coin. He assessed the transfer of their genetic endowments. In his interpretation, the offspring was not a result of the coalescence of the original maternal and paternal cells, but of the union of genetic endowments for individual traits of maternal and paternal plants. This revolutionary diagnostic method enabled Mendel to evaluate the results of the crossbreeding of seven pairs of pea plant's traits, where all the crossings were based on the principle of dominance and recessivity of the contrapositive traits.

When pairing the counterparts for fertilization, he applied the principle of complementarity. Complementary to man is woman. Man to man or woman to woman are not complementary. Complementary to the colour yellow of a mature pea plant seed is the colour green, complementary to a tall pea plant is the small pea plant, etc. Complementarity is the principle that explains the origin and the development of the traits of organisms within the system called life. Complementary to life is death.

You can find more information about the experiment in the presentation Gregor Mendel - His Hybridisation Discoveries and their Significance.

Mendel’s Laws

Mendel formulated his fundamental laws of hereditary in 1866. They were based on the analysis of the genetic crossbreeding between the cultivated, i.e. producing offspring with identical traits as their parents, pea plants (Pisum sativum), differing in particular, well-defined traits, such as the shape of the seeds (round or angular), the colour of the seeds (yellow or green) or the colour of the blossom (violet or white).

 

Mendel discovered that crossing the parental plants (P) which differ in one trait only, e.g. the shape of the seeds, yields offspring (F, first subsidiary generation) where all specimens inherit a trait from only one parental plant, in this case round seeds (see Fig. 4 and 5). The trait observable with the F1 generation is called dominant, the alternative traits are called recessive. In generation F2 (offspring of F1 parental plants), the dominant traits are inherited by three quarters of the offspring, the recessive traits by the remaining one quarter. The pea plant with recessive trait yields direct offspring, i.e. the result of crossing between the recessive F2 generations is the offspring F3, also inheriting the recessive trait. However, the specimens of the F2 generation with the dominant trait are divided into two categories: one third yields homogenous offspring, while the rest yields offspring where the proportion of the dominant traits to the recessive traits is 3 to 1 (as with the F2 generation).

 

Mendel hypothesized about this phenomenon and stated that various pairs of contrasting traits are each a result of a factor (nowadays called a gene) which has alternative forms (allels). Each plant contains a pair of genes which define a particular trait; each parental plant provided one gene. The allels defining the shape of the seed are labelled "R" for round seeds and "r" for angular seeds.

Two genotypes - structures of genes - are possible:

  1. plants from the homogeneous lineage with either round or angular seeds have the RR or rr genotypes, they are known as homozygotes in the shape of the seeds;
  2. plants with the Rr genotype are known as heterozygotes in the shape of the seeds and their phenotype, the manifestation of the trait, is round seeds because R is a dominant trait. These two allels never interbreed and are passed down to the offspring through gametes.

Mendel also proved that different traits are inherited independently. For example, crossing a pea plant with round yellow seeds (RRYY) with a pea plant with angular green seeds (rryy) yields offspring F1 (RrYy) with round yellow seeds (yellow seeds are dominant as opposed to green seeds). Phenotypes' F2 ratio was 9 round yellow : 3 round green : 3 angular yellow : 1 angular green.  This result demonstrates that none of the parents' genes tend to integrate (see Fig. 6).

 

Summary of Mendel’s laws

  1. 1.     Crossing homozygotes (F1 generation) yields offspring which are homogenous both in their genotypes and phenotypes
    - law of homogeneity of the first generation of hybrids.
  2. 2.     Crossing heterozygotes (F2 generation) yields offspring which are heterogeneous both in their genotypes and phenotypes, and the proportional representation of homozygotes and heterozygotes among the offsprings (and both dominant and recessive phenotypes) is regular and constant
    - law of segregation of alleles and their combination in the second generation of hybrids.
  3. 3.     Crossing heterozygotes (F3 generation) in more genetic pairs yields offspring which are heterogeneous both in their genotypes and phenotypes, and for which the proportional representation (9 : 3 : 3 : 1) of genotypes of all possible combinations between different alleles of all heterozygoteous alleles pairs is regular and constant 
    - law of free (independent) combination of alleles of various alleles pairs.

Almost all of Mendel's contemporaries chose to ignore his theory of hereditary. It was partially due to his application of the theory of probability in his calculations, which was an unknown ground for most the biologists at that time.

In 1900, Mendel's work was rediscovered and his laws were shown to be applicable to the heredity of plants as well as animals.

Mendel's work laid the foundations for a new scientific discipline which investigates the passing of genetic information from one generation to another, and examines the mutual relations between genetic units and traits, and their relation to the environment. His work did not intrigue scientists until the beginning of the 20th century, 16 years after his death.