Pimpinelli S, Ripoll P
Proc Natl Acad Sci U S A. 1986 Jun;83(11):3900-3. doi: 10.1073/pnas.83.11.3900.
Mitotic recombination is widely used in Drosophila as a technique to study genetic and developmental problems. It has been generally assumed that, following mitotic exchange between homologous chromatids during the G2 stage, the centromeres attached to the chromatids involved in the exchange segregate randomly. As a result, two equally frequent types of segregation, yielding genetically different products, are produced. However, when epidermal or enzymatic cell-marker mutants are used, only one type of segregation gives rise to marked cells. In the present work we test this assumption of random segregation using cytological markers. With cytological markers, larval neuroblast cells resulting from mitotic recombination exhibit recognizably all possible products from mitotic recombination. We find that one type of segregation is favored, in that, after mitotic recombination, the centromeres attached to the chromatids involved in the mitotic exchange preferentially migrate to opposite poles during anaphase. This favored segregation could be the result of exchange between previously oriented chromatids or could be due to the effect of the exchange upon subsequent orientation of homologous chromosomes. In either case, frequencies of mitotic recombination have been overestimated in the past.
有丝分裂重组在果蝇中被广泛用作研究遗传和发育问题的技术。一般认为，在G2期同源染色单体之间发生有丝分裂交换后，与参与交换的染色单体相连的着丝粒会随机分离。结果，产生了两种频率相等的分离类型，产生了基因不同的产物。然而，当使用表皮或酶细胞标记突变体时，只有一种分离类型会产生标记细胞。在本研究中，我们使用细胞学标记来检验这种随机分离的假设。使用细胞学标记，有丝分裂重组产生的幼虫神经母细胞表现出有丝分裂重组所有可能识别的产物。我们发现一种分离类型更受青睐，即有丝分裂重组后，与参与有丝分裂交换的染色单体相连的着丝粒在后期优先迁移到相反的两极。这种受青睐的分离可能是先前定向染色单体之间交换的结果，也可能是交换对同源染色体后续定向产生的影响。无论哪种情况，过去有丝分裂重组的频率都被高估了。
