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J. G. Mendel

(*1822 - †1884)
laid the foundations of genetics

J. G. Mendel when teaching in Brno - phototgraph taken in 1862

Biographical key dates

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 languge was German.


Fig. 1 - Birth house in Hynčice - before 1910

After the elementary school attended in Hynčice and the general grammar school in Opava, in 1840 he enrolled at the Philosophic Institute at the University of Olomouc. In 1843 he was admitted to the Augustinian monastery of St. Thomas in the Old Brno as a novice. He accepted the name Gregor. The Brno Augustinian monks were renowned scholars who actively participated both in university and grammar school education in the whole monarchy. At that time they held a significant position 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 Philosophic Institute in Brno. In 1853 he successfully finished his two-year studies at the University of Vienna.


Fig.1 - Brno at the time when Mendel entered the Augustinian monastery

In 1856 Mendel commenced his experiments with crossbreading plants, namely the pea plant, and in 1862 he began the meteorological monitorings for the Institute of Meteorology in Vienna. His meteorological monitorings were conducted with exceptional accuracy and continued unitl 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 "The Origin of the Species", he presented the first part of his theory on transmitting of hereditary traits. A month later, 8 March 1865, he delivered the second part of his theory. In 1866 his short monography, "Experiments with Plant Hybrids", was published.

In 1866 he was appointed abbot and prelate of the Agustinian monastery in Brno.

A year later he received a recognition for the first and only time in his life in the 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). 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 in the monastery. He was burried in the Augustinian tomb at the Brno's Central Cemetery. The requiem in the church was later conducted by a 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 then assessed the transmission 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 recesivity of the contrapositive traits. When pairing the countreparts 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 yellow colour of a mature pea plant seed is the green colour, 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.

Mendel's experiments

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 offsprings with identical traits as their parents, pea plants (Pisum sativum), differring in a 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).


Fig. 1 - Crossing the pea plants producing round seeds with pea plants producing angular seeds yields offsprings F1 with round seeds only. Crossing the F1 pea plant yields offsprings F2 with three quarters of the seeds being round and one quarter of them being angular.

Mendel discovered that crossing the parental plants (P) which differ in one trait only, e.g. the shape of the seeds, yields offsprings (F1, first subsidiary generation) where all speciemens 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 (offsprings of F1 parental plants), the dominant traits are inherited by three quarters of the offsprings, the recessive traits by the remaining one quarter. The pea plant with recessive trait yields direct offsprings, i.e. the result of crossing between the recessive F2 generations is the offsprings F3, also inheriting the recessive trait. However, the speciemens of the F2 generation with the dominant trait are divided into two categories: one third yields homogenous offsprings, while the rest yields offsprings where the proportion of the dominant traits to the recessive traits is 3 to 1 (as with F2 generation).


Fig. 1 - When crossbreeding the pea plant producing round seeds with the pea plant producing angular seeds, the F1 generation inherits the genotype of the round seeds because the trait for round seeds is dominant to the trait for the angular seeds. Three quarters of the F2 generation's seeds are round and one quarter of them is angular because the allels of these genes are trasmitted by independent haploid gametes.

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

Two genotypes - structures of genes - are possible:

  1. plants from the homogenous 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 thorugh gametes are transmitted onto the offsprings.

Mendel also proved that different traits were inherited independently. E.g. crossing a pea plant with round yellow seeds (RRYY) with a pea plant with angular green seeds (rryy) yields offsprings 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 genes from none of the parents tend to integrate (see Fig. 6).


Fig. 1 -  The genes for round seeds (R) or angular seeds (r), and for yellow seeds (Y) or green seeds (y) of pea plants seperate independently. The offsprings F2 comprise 9 genotypes including all four possible phenotypes.

Summary of Mendel's laws:

  1. Crossing homozygotes (F1 generation) yields offsprings which are homogenous both in their genotypes and phenotypes
    - law on homogeneity of the first generation of hybrids
  2. Crossing heterozygotes (F2 generation) yields offsprings 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 on segregation of alleles and their combination in the second generation of hybrids.
  3. Crossing heterozygotes (F3 generation) in more genetic pairs yields offsprings 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 on free (independent) combination of alleles of various alleles pairs.

Virtually all Mendel's contemporaries chose to ignore his theory of hereditary. Partially it was due to his application of the theory of probability, which for most the biologists at that time was an unknown ground.

In 1900 Mendel's work was rediscovered and established that his laws were applicable to hereditery both of plants and animals.

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