Gregor Mendel, known as the "father of modern genetics," was born in Austria in 1822. He was born into a family of Moravian peasants and proved to be very talented.
In 1843, Mendel entered the Augustinian Monastery in Brno (in what is now the Czech Republic) as a novice. In his autobiography, Mendel said that unlike other clerics, he didn't feel called to the Church: "my circumstances decided my vocational choice." Mendel did have a good life at the monastery; he was part of the cultural and scientific circles of the area. Also, the monastery sent him to school to continue his education.
Mendel had many interests, and while at the University of Vienna (1851-1853) he studied physics under Christian Doppler, and took courses in chemistry and zoology. As part of his monasterial duties, Mendel taught high school science at the local schools, and was remembered as a kind and good teacher.
Around 1854, Mendel began to research the transmission of hereditary traits in plant hybrids. At the time of Mendel’s studies, it was a generally accepted fact that the hereditary traits of the offspring of any species were merely the diluted blending of whatever traits were present in the “parents.” It was also commonly accepted that, over generations, a hybrid would revert to its original form, the implication of which suggested that a hybrid could not create new forms. Mendel's Pisum experiments involved crossing and testing a large quantity of selected plants. Between 1854 and 1863, he studied nearly 28,000 plants. His aim was to examine how the plant's characters were passed on from generation to the next. The plants of genus Pisum have quite distinct characters in seeds and in plants that are easily distinguishable and they yield perfectly fertile hybrids. In Mendel's terms, a hybrid is the product of the first crossing, or the F1 generation .
In his first experiment, Mendel crossed a purebred round seed with a purebred angular seed and the result was that all of the hybrids were round. They acquired the shape from the round-seeded parent. He then planted the round hybrid seeds which self-fertilized (became the F2 generation), which resulted in 5,474 round seeds compared to 1,850 angular seeds. From this finding, Mendel concluded that the characters segregate in a ratio of 3:1. Because the round-seeded hybrids prevailed over the angular-seeded hybrids, the round trait is known as dominant, while the angular trait is the recessive. This finding rejects the notion of blended inheritance. Mendel continued his experiments in subsequent generations (to four generations), which other naturalists have never considered.
Gregor Mendel's experiments with plant hybridization gave way to what is now known as the Mendelian Theory in modern genetics. This theory states that an individual has two genes, factors that determine the hereditary transmission of characters, for each character. The two genes may be the same or different. The different genes are called alleles. Mendel's experiments revealed the existence of dominant allele (A) and recessive (a). The parent plants are the (A) and (a) alleles, which form the hybrid (Aa). The (A) is the dominant allele, so (AA) and (Aa) would both exhibit the dominant trait(Mendel, 1950). The test cross method, developed by Mendel, is a useful tool in predicting the genotype of an organism. In today's terminology, a homozygous dominant trait (AA) is crossed with a homozygous recessive trait (aa) to yield four heterozygotes, each with the only A genotype expressed.
After 1900, Pisum experiments were conducted in England confirming Mendel's findings. Mendel is credited with the fundamental discovery of the physical unit of heredity. He has been described as "giving birth" to an entirely new theory, laying the foundation for a completely new line of research.
However,Mendel's work was rejected at first, and was not widely accepted until after he died. During his own lifetime, most biologists held the idea that all characteristics were passed to the next generation through blending inheritance, in which the traits from each parent are averaged together. Instances of this phenomenon are now explained by the action of multiple genes with quantitative effects. Charles Darwin tried unsuccessfully to explain inheritance through a theory of pan genesis. It was not until the early 20th century that the importance of Mendel's ideas was realized.
By 1900, research aimed at finding a successful theory of discontinuous inheritance rather than blending inheritance led to independent duplication of his work by Hugo de Vries and Carl Correns, and the rediscovery of Mendel's writings and laws. Both acknowledged Mendel's priority, and it is thought probable that de Vries did not understand the results he had found until after reading Mendel.Though Erich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understand Mendel's laws. Though de Vries later lost interest in Mendelism, other biologists started to establish genetics as a science.
Mendel's results were quickly replicated, and genetic linkage quickly worked out. Biologists flocked to the theory; even though it was not yet applicable to many phenomena, it sought to give a genotypic understanding of heredity which they felt was lacking in previous studies of heredity which focused on phenotypic approaches.
Besides his work on plant breeding while at St Thomas's Abbey, Mendel also bred bees in a bee house that was built for him, using bee hives that he designed. He also studied astronomy and meteorology, founding the Austrian Meteorological Society in 1865. The majority of his published works were related to meteorology.
Source: Wikipedia and various other random offline sources.