Institut Pasteur, Group Spatial Regulation of Genomes, Department of Genomes and Genetics, F-75015 Paris, France.
Genetics. 2012 Jun;191(2):309-17. doi: 10.1534/genetics.112.139733.
The segregation and random assortment of characters observed by Mendel have their basis in the behavior of chromosomes in meiosis. But showing this actually to be the case requires a correct understanding of the meiotic behavior of chromosomes. This was achieved only gradually, over several decades, with much dispute and confusion along the way. One crucial step in the understanding of meiosis was provided in 1909 by Frans Alfons Janssens who published in La Cellule an article entitled "La théorie de la Chiasmatypie. Nouvelle interprétation des cinèses de maturation," which contains the first description of the chiasma structure. He observed that, of the four chromatids present at the connection sites (chiasmata sites) at diplotene or anaphase of the first meiotic division, two crossed each other and two did not. He therefore postulated that the maternal and paternal chromatids that crossed penetrated the other until they broke and rejoined in maternal and paternal segments new ways; the other two chromatids remained free and thus intact. This allowed him also to propose that the chromatids distributed in the four nuclei issued from the second meiotic division had various combinations of maternal and paternal segments of each chromosome. And conversely, permitted the appreciation that the laws of Mendelian segregation required breakage and joining (crossing over) between homologous non-sister chromatids. Although Janssens's article found a broad appreciative audience and had a large influence on the chromosomal theory at that time, his theory was resisted by both geneticists and cytologists for several decades. This Perspectives aims to highlight the novelty of Janssens's chiasmatype theory by examining the historical background and our actual understanding of meiotic recombination.
孟德尔所观察到的遗传性状的分离和随机组合，其基础是染色体在减数分裂中的行为。但是，要证明这一点实际上需要正确理解染色体的减数分裂行为。这一理解是在几十年的时间里逐步实现的，其间存在着许多争议和混乱。弗朗斯·阿尔方斯·詹森斯（Frans Alfons Janssens）在 1909 年发表在《La Cellule》上的一篇题为“Chiasmatypie 理论。成熟减数分裂的新解释”的文章中，为理解减数分裂提供了一个关键步骤，其中包含了第一个关于交叉结构的描述。他观察到，在第一次减数分裂的双线期或后期，在连接点（交叉点）存在的四个染色单体中，两个相互交叉，两个不交叉。因此，他假设交叉的母本和父本染色单体穿透另一个，直到它们断裂并在母本和父本片段的新位置重新连接；另外两个染色单体保持自由，因此保持完整。这也使他能够提出，在第二次减数分裂中分布在四个核中的染色单体具有每个染色体的母本和父本片段的各种组合。相反，这也使得人们认识到孟德尔分离定律要求同源非姐妹染色单体之间发生断裂和连接（交叉互换）。尽管詹森斯的文章受到了广泛的赞赏，并对当时的染色体理论产生了很大的影响，但他的理论在几十年内都受到遗传学家和细胞学家长期抵制。本文旨在通过考察减数重组的历史背景和我们当前的理解，突出詹森斯的交叉类型理论的新颖性。
