against gray-brown seed coat with purple flower; smooth pod against constricted pod; green pod against yellow pod; axillary flowers against terminal flowers; tall stems against dwarf. And while the differing varieties hybridized in the garden behind the monastery, in his mind the logic of algebra hybridized with the facts of life.
(A + a)(A + a) = AA + 2Aa + aa
That is all it is, you see—the secrets of inheritance speared on the point of a simple binomial expansion. There is all the simplicity of genius. But what is the complexity beneath?
Year One (1856)
A total of 287 artificial crossings were carried out with seventy different plants from the selected pure varieties ( A × a ).
Year Two (1857)
Hybrids ( Aa ) from the first-year crossings were planted out and scored. Exact numbers unknown, but there were 511 hybrid plants counted for seed shape and color alone. These hybrids were left to self-pollinate (which is what they do naturally) and the peas collected, dried, and labeled for the next year.
Year Three (1858)
Four thousand six hundred twelve offspring from the previous year were planted out. They were counted and scored. In this generation the famous three-to-one ratios between dominant types ( AA or Aa ) and recessive types ( aa ) appeared. Individual dwarf plants were lifted and potted as soon as recognized, to ensure that they were not shaded by their tall neighbors. (He had a clear idea of the contrast between the inherited and the acquired, you see. He distinguished nature from nurture.) Again, self-pollination was allowed to take place in all plants. In this year Mendel also began to set up combinations of two or more characters together on the same plant—the bi- and trifactorial crosses.
Year Four (1859)
In this generation it was shown that all the recessive types from the previous year had produced nothing but recessive offspring, i.e., they were genetically pure. Of dominant types, some (one-third) were now shown to have been genetically pure, while the remainder (two-thirds) again produced dominant and recessive offspring in a three-to-one ratio, showing that they had been carrying the recessive character (i.e., were genetically impure hybrids). This was revealed by selecting one hundred of each of the 1858 dominant types and planting out ten seeds from each plant. This alone yields one thousand plants. In this year there are also the hybrids from the bifactorial and trifactorial crossesthat were set up in 1858. Going through his paper, you lose count. From 1859 it becomes impossible to calculate with any accuracy the numbers of plants involved. Fisher 2 suggests over five thousand plants for 1859, and over six thousand for 1860. The greenhouse was working full-time. Row upon row of peas grew in the garden strip behind the monastery. Obsession? Possession? The friar was at once their master and their slave. The work became the focus that drew to itself all the perspective lines of his world, the vanishing point of the whole of his existence. All else—personal inadequacy, nagging spiritual doubts, ailing mother, dead father—disappeared as surely as the demons of night disappear in the plain light of day. The good friar had slipped his moorings and was away on the high seas, leaving ordinary mortals far behind. Land was out of sight below the horizon.
Year Five (1860)
Some monofactorial lines are continued to show that half of the offspring of hybrids breed true, i.e., are genetically exactly as pure as the original stock lines that started the whole work. The second generation from the first bifactorial and trifactorial crossings are also planted out, producing plants with all possible combinations of characters, and showing that a pair of factors controlling one character is inherited entirely separately from a pair of factors controlling another character (what became the so-called “second law”). In that year he also back-crossed double hybrids ( AaBb ) with pure recessives from the
(A + a)(A + a) = AA + 2Aa + aa
That is all it is, you see—the secrets of inheritance speared on the point of a simple binomial expansion. There is all the simplicity of genius. But what is the complexity beneath?
Year One (1856)
A total of 287 artificial crossings were carried out with seventy different plants from the selected pure varieties ( A × a ).
Year Two (1857)
Hybrids ( Aa ) from the first-year crossings were planted out and scored. Exact numbers unknown, but there were 511 hybrid plants counted for seed shape and color alone. These hybrids were left to self-pollinate (which is what they do naturally) and the peas collected, dried, and labeled for the next year.
Year Three (1858)
Four thousand six hundred twelve offspring from the previous year were planted out. They were counted and scored. In this generation the famous three-to-one ratios between dominant types ( AA or Aa ) and recessive types ( aa ) appeared. Individual dwarf plants were lifted and potted as soon as recognized, to ensure that they were not shaded by their tall neighbors. (He had a clear idea of the contrast between the inherited and the acquired, you see. He distinguished nature from nurture.) Again, self-pollination was allowed to take place in all plants. In this year Mendel also began to set up combinations of two or more characters together on the same plant—the bi- and trifactorial crosses.
Year Four (1859)
In this generation it was shown that all the recessive types from the previous year had produced nothing but recessive offspring, i.e., they were genetically pure. Of dominant types, some (one-third) were now shown to have been genetically pure, while the remainder (two-thirds) again produced dominant and recessive offspring in a three-to-one ratio, showing that they had been carrying the recessive character (i.e., were genetically impure hybrids). This was revealed by selecting one hundred of each of the 1858 dominant types and planting out ten seeds from each plant. This alone yields one thousand plants. In this year there are also the hybrids from the bifactorial and trifactorial crossesthat were set up in 1858. Going through his paper, you lose count. From 1859 it becomes impossible to calculate with any accuracy the numbers of plants involved. Fisher 2 suggests over five thousand plants for 1859, and over six thousand for 1860. The greenhouse was working full-time. Row upon row of peas grew in the garden strip behind the monastery. Obsession? Possession? The friar was at once their master and their slave. The work became the focus that drew to itself all the perspective lines of his world, the vanishing point of the whole of his existence. All else—personal inadequacy, nagging spiritual doubts, ailing mother, dead father—disappeared as surely as the demons of night disappear in the plain light of day. The good friar had slipped his moorings and was away on the high seas, leaving ordinary mortals far behind. Land was out of sight below the horizon.
Year Five (1860)
Some monofactorial lines are continued to show that half of the offspring of hybrids breed true, i.e., are genetically exactly as pure as the original stock lines that started the whole work. The second generation from the first bifactorial and trifactorial crossings are also planted out, producing plants with all possible combinations of characters, and showing that a pair of factors controlling one character is inherited entirely separately from a pair of factors controlling another character (what became the so-called “second law”). In that year he also back-crossed double hybrids ( AaBb ) with pure recessives from the
Similar Books
