生物學
1866
植物雜交實驗
性狀以一個個離散、隱藏的單位代代相傳，按簡單的比例分離、隱沒、又重現。
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透過種豌豆、並仔細清點後代，一位修士發現：性狀是以一個個細小、獨立的「小包裹」傳下去的——那就是我們今天所說的基因。
核心想法
過去人們以為，孩子的性狀不過是父母的混合——把一株高的和一株矮的配在一起，就該得到一株中等高的。孟德爾耐心地培育了成千上萬株豌豆，發現的卻是另一回事。把一株高豌豆和一株矮豌豆雜交，下一代裡每一株都是高的。「矮」並沒有被混淡、也沒有消失——它只是藏了起來。
再讓這些植株繁育下去，「矮」又會在接下來的一代裡冒出來，比例幾乎恰好是每四株裡有一株。正是這個工整的比例，洩露了祕密。每株植物，一定都攜帶著兩條關於高矮的隱藏指令，分別來自父母，而它只把其中一條傳下去。有些指令「聲音響」（顯性），有些「聲音輕」（隱性）——而一條「輕」的指令，可以隱匿一代，再原封不動地重現。
它是如何誕生的
格雷戈爾·孟德爾，是布呂恩（今布爾諾）一所修道院裡的修士兼教師。在那座花園裡，他用了約八年時間，種下並親手授粉了數以萬計的豌豆，逐一追蹤單個性狀，像會計記帳一樣清點結果。1865 年，他把發現報告給當地的自然史學會，並於 1866 年發表。
然後——幾乎沒有任何回響。對那個年代的生物學家來說，這工作太「數學」了，於是無人問津，擱置了 34 年。直到 1900 年，三位植物學家各自獨立地，撞上了同樣的規則，又翻出了孟德爾那篇被遺忘的論文。而那時，他已去世十六年。
它為何重要
孟德爾發現了遺傳的基本規則——性狀以離散的單位傳遞，牠們並不混合，而是按可預測的概率重新洗牌、再度現身。他那被同代人忽視的數豌豆工作，後來成了遺傳學、以及由此生長出來的一切的基石——從作物育種，到對遺傳病的預測。
一個可以想像的畫面
想像每個親本，就一種性狀各握著兩張牌，並隨機地只發一張給孩子。「高」是一張搶眼的牌，只要在場就顯出來；「矮」則是一張害羞的牌，唯有當孩子恰好拿到兩張時，才會現身。讓兩個 Tt 的親本各發一張牌，平均而言，每四個孩子裡有三個顯高、一個顯矮。把所有組合擺出來，便是一格龐尼特方格——到下面試試看。
它的位置
達爾文已經表明，生命靠自然選擇演化，卻缺少一套遺傳的機制——而「後代不過是父母的混合」這一流行想法，本會把任何新出現的變異稀釋殆盡。孟德爾的「顆粒式」因子，正是那塊缺失的拼圖：牠們整個地傳下去，於是變異得以保留。數十年後，兩套思想被熔合為「現代綜合」，而孟德爾那抽象的因子，終於在 DNA 雙螺旋中獲得了一具身軀。
Original source text
引言與豌豆的選擇
Experience of artificial fertilisation, such as is effected with ornamental plants in order to obtain new variations in colour, has led to the experiments which will here be discussed. The striking regularity with which the same hybrid forms always reappeared whenever fertilisation took place between the same species induced further experiments to be undertaken, the object of which was to follow up the developments of the hybrids in their progeny.
Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations.
The selection of the plant group for experiments of this kind must be made with all possible care if it be desired to avoid from the outset every risk of questionable results. The experimental plants must necessarily possess constant differentiating characters, and their hybrids must be protected from the influence of all foreign pollen during the flowering period. The genus Pisum was found to possess the necessary qualifications.
顯性與隱性性狀
The characters which were selected for experiment relate to the form of the ripe seed (round or wrinkled); the colour of the seed albumen (yellow or green); the length of the stem (tall or dwarf); and four others — seven differentiating characters in all, each appearing in two clear, non-blending forms.
Those characters which are transmitted entire, or almost unchanged in the hybridisation, and therefore in themselves constitute the characters of the hybrid, are termed the dominant, and those which become latent in the process recessive.
The expression “recessive” has been chosen because the characters thereby designated withdraw or entirely disappear in the hybrids, but nevertheless reappear unchanged in their progeny. Transitional forms were not observed in any experiment.
第一代與第二代：3∶1
In the first generation from the crossing, every hybrid plant displays the dominant character, and the recessive form escapes observation completely. It is, moreover, perfectly immaterial whether the dominant character belongs to the seed-bearer or to the pollen-parent; the form of the hybrid is identical in both cases.
In this generation there reappear, together with the dominant characters, also the recessive ones with their peculiarities fully developed, and this occurs in the definitely expressed average proportion of three to one, so that among each four plants of this generation three display the dominant character and one the recessive.
Of 8023 seeds from one experiment, 6022 were yellow and 2001 green — a ratio of 3.01 to 1. In another, of 7324 seeds, 5474 were round and 1850 wrinkled — 2.96 to 1. The whole of the experiments yielded the average ratio 2.98 to 1.
2∶1∶1 的拆解
Those forms which in the next generation again breed true to the dominant character are revealed to be of two kinds. The dominant offspring are not uniform: one third of them breed true, while two thirds behave as hybrids — themselves splitting 3 : 1 in the generation that follows.
The relation of three to one, in which the distribution of the dominant and recessive characters results in the first generation, resolves itself therefore in all experiments into the proportion of 2 : 1 : 1 if at the same time the dominant character be distinguished according to its significance as a hybrid-character or as a parental one.
組合的法則
Pea hybrids form germinal and pollen cells which, in their composition, correspond in equal numbers to all the constant forms resulting from the combination of the characters united in fertilisation. The behaviour of each pair of differentiating characters in hybrid union is independent of the other differences in the two original parental stocks.
It is now clear why, in a hybrid plant, the differentiating characters can re-emerge in their parental purity: each germ cell and each pollen cell carries only one of the two. The constancy of the offspring, and the definite numerical ratios in which the forms appear, follow of necessity.
Read at the meetings of February 8 and March 8, 1865