Ahli botani Gregor Mendel

Penafsiran teoretis

Mendel melanjutkan untuk menghubungkan hasil-hasilnya dengan teori pembuahan sel, yang dengannya suatu organisme baru dihasilkan dari perpaduan dua sel. Agar pemuliaan murni dari jenis dominan dan resesif untuk dibawa ke dalam hibrida, harus ada akomodasi sementara dari dua karakter yang berbeda dalam hibrida serta proses pemisahan dalam pembentukan sel-sel serbuk sari dan sel-sel telur. Dengan kata lain, hibrida harus membentuk sel benih yang mengandung potensi untuk menghasilkan salah satu karakteristik atau lainnya. Ini sejak itu telah digambarkan sebagai hukum segregasi, atau doktrin kemurnian sel-sel benih. Karena satu sel serbuk sari menyatu dengan satu sel telur, semua kemungkinan kombinasi serbuk sari dan sel telur yang berbeda akan menghasilkan hanya hasil yang disarankan oleh teori kombinatorial Mendel.

Mendel pertama kali mempresentasikan hasilnya dalam dua kuliah terpisah pada tahun 1865 kepada Lembaga Ilmu Pengetahuan Alam di Brünn. Makalahnya "Eksperimen pada Hibrida Tanaman" diterbitkan dalam jurnal masyarakat, Verhandlungen des naturforschenden Vereines di Brünn, pada tahun berikutnya. Itu menarik sedikit perhatian, meskipun banyak perpustakaan menerimanya dan cetak ulang dikirim. Kecenderungan orang-orang yang membacanya adalah untuk menyimpulkan bahwa Mendel hanya menunjukkan dengan lebih akurat apa yang sudah diasumsikan secara luas — yaitu, bahwa keturunan hibrida kembali ke bentuk asalnya. Mereka mengabaikan potensi variabilitas dan implikasi evolusioner yang memungkinkan demonstrasi rekombinasi sifat-sifatnya. Terutama, ahli botani Swiss Karl Wilhelm von Nägeli sebenarnya berkorespondensi dengan Mendel,meskipun tetap skeptis mengenai signifikansi hasil dan meragukan bahwa sel benih dalam hibrida bisa murni.

Latter years

Mendel appears to have made no effort to publicize his work, and it is not known how many reprints of his paper he distributed. He had ordered 40 reprints, the whereabouts of only eight of which are known. Other than the journal that published his paper, 15 sources are known from the 19th century in which Mendel is mentioned in the context of plant hybridization. Few of these provide a clear picture of his achievement, and most are very brief.

By 1871 Mendel had only enough time to continue his meteorological and apicultural work. He traveled little, and his only visit to England was to see the Industrial Exhibition in 1862. Bright disease made his last years painful, and he died at the age of 61. Mendel’s funeral was attended by many mourners and proceeded from the monastery to the monastery’s burial plot in the town’s central cemetery, where his grave can be seen today. He was survived by two sisters and three nephews.

Rediscovery

In 1900 Dutch botanist and geneticist Hugo de Vries, German botanist and geneticist Carl Erich Correns, and Austrian botanist Erich Tschermak von Seysenegg independently reported results of hybridization experiments similar to Mendel’s, though each later claimed not to have known of Mendel’s work while doing their own experiments. However, both de Vries and Correns had read Mendel earlier—Correns even made detailed notes on the subject—but had forgotten. De Vries had a diversity of results in 1899, but it was not until he reread Mendel in 1900 that he was able to select and organize his data into a rational system. Tschermak had not read Mendel before obtaining his results, and his first account of his data offers an interpretation in terms of hereditary potency. He described the 3:1 ratio as an “unequal valancy” (Wertigkeit). In subsequent papers he incorporated the Mendelian theory of segregation and the purity of the germ cells into his text.

In Great Britain, biologist William Bateson became the leading proponent of Mendel’s theory. Around him gathered an enthusiastic band of followers. However, Darwinian evolution was assumed to be based chiefly on the selection of small, blending variations, whereas Mendel worked with clearly nonblending variations. Bateson soon found that championing Mendel aroused opposition from Darwinians. He and his supporters were called Mendelians, and their work was considered irrelevant to evolution. It took some three decades before the Mendelian theory was sufficiently developed to find its rightful place in evolutionary theory.

The distinction between a characteristic and its determinant was not consistently made by Mendel or by his successors, the early Mendelians. In 1909 Danish botanist and geneticist Wilhelm Johannsen clarified this point and named the determinants genes. Four years later American zoologist and geneticist Thomas Hunt Morgan located the genes on the chromosomes, and the popular picture of them as beads on a string emerged. This discovery had implications for Mendel’s claim of an independent transmission of traits, for genes close together on the same chromosome are not transmitted independently. Moreover, as genetic studies pushed the analysis down to smaller and smaller dimensions, the Mendelian gene appeared to fragment. Molecular genetics has thus challenged any attempts to achieve a unified conception of the gene as the elementary unit of heredity. Today the gene is defined in several ways, depending upon the nature of the investigation. Genetic material can be synthesized, manipulated, and hybridized with genetic material from other species, but to fully understand its functions in the whole organism, an understanding of Mendelian inheritance is necessary. As the architect of genetic experimental and statistical analysis, Mendel remains the acknowledged father of genetics.