It’s hard to imagine a time when we didn’t understand how traits were passed from generation to generation. Before the 1800s, it was clear that traits were passed down just by looking at the similarities between family members. Farmers understood this for centuries, choosing to plant seeds from the most ideal crops. Ranchers understood this too, only allowing the best pigs, cattle, chickens, etc. to breed. Of course nobody truly understood the mechanism behind heredity. Chromosomes, Genes, DNA, or Genetics had not been discovered yet.
Humans have been thinking about heredity for centuries. Aristotle was the first to suggest there must be something like a code passed from generation to generation all the way back in the 300s BCE. Scientific thought on the matter didn’t expand further until the 1520s. This is when the idea of preformation first took root. Basically, it proposed that the mother had no role in the outcome of the child. The father’s gametes contained a mini-human that was transferred to the mother and inflated before birth. This idea was logically flawed. If the “inflating” min-human became an adult, then it would have to mini-humans in its gametes. Tiny humans encased inside tiny humans, and so on, like an infinite series of Russian nesting dolls, stretching all the way back to the first humans.
Scientific thinking about heredity was purely theoretical during Mendel’s early life in the 1800s. For instance, Charles Darwin published his famous Origin of Species in 1859, but was nearly driven to a nervous breakdown afterwards trying to uncover the mechanism by which heredity worked. In 1867 he published a book proposing that the cells from all over the body produced tiny particles he called gemmules that entered the sperm/egg/gamete during reproduction. He thought the gemmules contained the information for making a new person, and when a sperm met an egg, the information blended together. This idea was deeply flawed. For instance, if there was constant blending taking place during every act of conception, then the entire human population should slowly trend towards the same blend of traits. Also.. if a parent had lost an arm in an accident, there should be no “arm gemmules” to code for a new arm, and yet children always seem to be born with them anyways.
It was Gregor Mendel who alone uncovered the mechanism of heredity. He did it by himself, without being recognized or respected for his discoveries during his life. Gregor was born to German speaking parents in what is now the modern day Czech Republic. He grew up on a farm, being exposed to gardening and botany early on. Mendel joined the Augustinian St Thomas’ Abbey in Brno Czech Republic. Gregor worked as a substitute high school teacher, but failed the exam to become a certified teacher in 1850. Mendel went on to the University of Vienna in 1851, and returned to the Abbey in 1853. Gregor was given permission to begin his famous experiments on heredity in the Abbey’s 5 acre garden in 1854. Meanwhile, he attempted to qualify as a high school teacher a second time in 1856 and once again failed the oral component of his test.
Mendel returned from his failed exam, and began his famous experiments on pea plants. Gregor first started breeding pea plants for pure-bred traits. That means the traits would always remain in the next generation when self-fertilized.
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Seed Texture (smooth vs. wrinkled)
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Color of Seed (yellow vs. green)
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Color of the flower (white vs purple)
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The position of the flower.
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Color of the pea pod (green vs. yellow)
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Shape of the pea pod (smooth vs. crumpled)
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Height of the plant (tall vs. short)
These true-breeding pea plants had distinct traits that were hereditary. Bred to themselves, tall-stemmed plants generated only tall plants. Purple flowered plants made more purple plants, and so on for all 7 traits. Mendel started mating purebred pea plants with other purebred lines to create hybrids. His experimental question was simple. If he crossed a purple flowered and a white flowered plant, would he end up with pink offspring? Would the traits blend, which is what most people of the time believed. Mendel mated the pea plant flowers by hand. He started by cutting off the male reproductive organ (stamen/anther), then brushed the pollen from the male stamen onto the female reproductive organ (stigma) using a paintbrush. It was tedious work, and he worked alone.
By the late summer of 1857 the first hybrid peas had bloomed, in a scene of white and violet flowers. Gregor took notes on all of the purebred traits he had started with. He looked for blending in the traits, and didn’t see any in the first generation. In a stroke of pure genius he then mated some of the hybrids with other hybrid pea plants.
“The experiments progress slowly,” Mendel wrote. “At first a certain amount of patience was needed, but I soon found that matters went better when I was conducting several experiments simultaneously.” By repeating multiple experiments at the same time, Mendel produced enormous amounts of data, taking note of the traits observed after each pea mating.
The first pattern was easy to identify. In the first -generation hybrids, the individual hereditary traits - White vs. Purple flowers, or tallness and shortness did NOT blend at all. All tall plants crossed with a small one produced ONLY tall plants. Round-seeded peas crossed with wrinkled seeds produced ONLY round peas. All seven of his purebred traits followed this pattern. Mendel termed the overriding traits dominant, while the traits that had disappeared he called recessive.
“If Mendel had stopped his experiment here, he would already have made a major contribution to a theory of heredity. The existence of dominant and recessive alleles for a trait contradicted ninteenth-century theories of blending inheritance. The hybrids that Mendel generated did not have intermediate features. Only one allele had asserted itself in the hybrid, forcing the other variant trait to vanish.”(Muhkerjee, 2016)
In Gregor’s second famous experiment he bret short-tall hybrids with short-tall hybrids. The results were that the hidden recessive short trait reappeared after having disappeared for a generation. The same pattern occurred for all 7 purebred traits. The recessive trait reappeared at predictable ratios. For instance, after breeding hybrids together, ¼ of the offspring would show the trait. He acquired boat-loads of data which was amazingly consistent and clear. There are two alleles that determine a trait, and they are passed down randomly to the next generation, one from each parent.
Mendel continued his experiments between 1857 and 1864. In all, he produced data on 20,000 plants, 40,000 flowers, and nearly 4,000 seeds.
“It requires indeed some courage to undertake a labor of such far-reaching extent,” Mendel would later write.
Many discoveries in science seem to happen by accident or coincidence. This is not the case with Gregor Mendel. His deep knowledge of botany and gardening made him the perfect individual to conduct these experiment. J = 4. He was organized and precise, in a way that modern scientists would be impressed by.
In 1865, Mendel published and presented his work on peas in two parts. He spoke to a group of farmers, botanists, and biologists in Brno Czech Republic. Only about 40 people were there. The paper was a ROUGH read. It was filled with dozens of tables, mathematics, and mediocre writing. His paper was published in an obscure journal called Proceedings of the Brno Natural Society. Copies of his paper were sent to far and wide, to institutions like the Linnean Society in England, and the Smithsonian in Washington DC, among dozens of others. Mendel himself sent out dozens of copies to the leading scientists of the day.
What followed was one of the strangest silences in the history of biology. His epic and world-altering discoveries remained lost and unappreciated from 1866 until 1900. Mendel wrote many scientists with hopes of his research being recognized. He famously wrote to Botanist Carl von Nageli, who wrote back two months later criticizing Mendel as being an amateur scientist. Mendel continue writing Nageli, and he continued to dismiss his ideas. Nageli suggested using a different plant, the yellow-flowering hawkweed to repeat the results. This was a horrible choice. Neither scientist realized that hawkweed can reproduce asexually, and don’t even need their pollen or eggs. Mendel’s conducted the experiments but his data didn’t make any sense. He repeated the experiments again between 1867 and 1871, attempting to cross thousands of plants, but it was never destined to work.
Mendel’s letters to Nageli became more desperate. Nageli replied occasionally, but always in a dismissive and negative tone. He wrote his last letter to Nageli in November 1873, explaining that he was unable to complete the experiments. Gregor was promoted to the position of Abbot at the monastery in Brno, and he quickly became too busy for experimentation.
“I feel truly unhappy that I have to neglect my plants… so completely,” Mendel wrote.
The work of the monastery filled up the remainder of his life. Amazingly, he had written only one monumental paper on pea plant hybrids. His health declined in the 1880s, and he gradually gave up his duties at the monastery, all except for basic gardening. On January 1884, Mendel died of kidney failure, his feet swollen with fluids. The local newspaper wrote an obituary, but made no mention of his experimental studies. The obituary included a note from one of the monks at the monastery that read “Gentle, Free-handed, and kinly… Flowers he loved.”
By the late 1890s, Dutch botanist Hugo de Vries was on the verge of repeating Mendel’s discoveries in different plant hybrids. He must have been blown-away when a friend of him sent Mendel’s 1865 paper to his doorstep. I’m sure it must have been hard reading that someone had already discovered your life’s work three decades earlier. In a fit of shameful panic, de Vries rushed his paper on plant hybrids into publication in 1900, without any mention of Mendel’s previous work. This was a dastardly and unethical thing to do, and quickly backfired. De Vries was not alone in re-discovered Mendel’s paper. That same year Carl Correns published a paper on his hybrids between tall and short hybrids, and almost exact repeat of Mendel’s experiment. When researching to write a paper on his work, he came across Mendel’s long-lost paper and recognized his contributions in his own paper. A third scientist Erich von Tschermak also published a paper that recognized Mendel’s contributions.
De Vries’ paper that did not mention Mendel used the Gregor’s own terms, including dominant and recessive. In the spring of 1900 Carl Correns accused De Vries of plagiarism, stealing ideas from Mendel’s original and long-lost paper. In De Vries next paper he mentioned Mendel glowingly and acknowledged that he was simple “extending” Gregor’s work.
Famous biologist William Bateson was an instant convert to Mendel’s discoveries. He wrote....
“We are in the presence of a new principle of the highest importance. To what further conclusions it may lead us cannot yet be foretold.”
Bateson made it his personal mission that Mendel’s work would never again be ignored. He independently confirmed Mendel’s work on plant hybrids, and soon earned the nickname “Mendel’s Bulldog” as someone who fought for truth and significance of his lost discoveries. A group of scientists joined Bateson at Cambridge University in England to study a new field of science, a field Bateson called genetics. In greek the word means “to give birth.”
N40 AB.CDE W10F GH.JKL
A =
B = Gregor Mendel died in 188___
C = The number of scientists to have discovered DNA by the time of Mendel’s experiments.
D = The number of times Gregor Mendel failed an exam to become a high school science teacher.
E = 8 - (The number of purebred traits Gregor Mendel used during his experiments)
F = Gregor’s experimented on __0,000 flowers.
G = Mendel published his only paper in 186__
H =
J =
K = Mendel’s Research remained lost for over two decades. It was re-discovered in 1__00
L = The number of scientists who re-discovered Gregor Mendel’s during the same year.
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