Baker B S
Genetics. 1975 Jun;80(2):267-96. doi: 10.1093/genetics/80.2.267.
The effects of a male-specific meiotic mutant, paternal los (pal), in D. melanogaster have been examined genetically. The results indicate the following: (1) When homozygous in males, pal can cause loss, but not nondisjunction, of any chromosome pair. The pal-induced chromosome loss produces exceptional progeny that apparently failed to receive one, or more, paternal chromosomes and, in addition, mosaic progeny during whose early mitotic divisions one or more paternal chromosomes were lost. (2) Only paternally derived chromosomes are lost. (3) Mitotic chromosome loss can occur in homozygous pal+progeny of pal males. (4) Chromosomes differ in their susceptibility to pal-induced loss. The site responsible for the insensitivity vs. sensitivity of the X chromosome to pal mapped to the basal region of the X chromosome at, or near, the centromere. From these results, it is suggested that pal+acts in male gonia to specify a product that is a component of, or interacts with, the centromeric region of chromosomes and is necessary for the normal segregation of paternal chromosomes. In the presence of pal, defective chromosomes are produced and these chromosomes tend to get lost during the early cleavage divisions of the zygote. (5) The loss of heterologous chromosome pairs is not independent; there are more cases of simultaneous loss of two chromosomes than expected from independence. Moreover, an examination of cases of simultaneous somatic loss of two heterologs reveals an asymmetry in the early mitotic divisions of the zygote such that when two heterologs are lost at a somatic cleavage division, almost invariably one daughter nucleus fails to get either, and the other daughter nucleus receives its normal chromosome complement. It is suggested that this asymmetry is not a property of pal but is rather a normal process that is being revealed by the mutant. (6) The somatic loss of chromosomes in the progeny of pal males allows the construction of fate maps of the blastoderm. Similar fate maps are obtained using data from gynandromorphs and from marked Y chromosome (nonsexually dimorphic) mosaics.
对果蝇中一种雄性特异性减数分裂突变体——父本丢失（pal）的影响进行了遗传学研究。结果表明如下：（1）雄性纯合时，pal可导致任何染色体对的丢失，但不会导致不分离。pal诱导的染色体丢失产生异常后代，这些后代显然未能获得一条或多条父本染色体，此外，还产生嵌合体后代，在其早期有丝分裂过程中一条或多条父本染色体丢失。（2）只有父本来源的染色体丢失。（3）pal雄性的纯合pal+后代中可发生有丝分裂染色体丢失。（4）染色体对pal诱导丢失的敏感性不同。X染色体对pal不敏感与敏感的位点定位于X染色体着丝粒处或附近的基部区域。从这些结果推测，pal+在雄性生殖细胞中起作用，指定一种产物，该产物是染色体着丝粒区域的组成部分或与之相互作用，是父本染色体正常分离所必需的。在pal存在的情况下，会产生有缺陷的染色体，这些染色体在合子的早期卵裂过程中容易丢失。（5）异源染色体对的丢失不是独立的；同时丢失两条染色体的情况比独立情况下预期的要多。此外，对同时发生两条异源染色体体细胞丢失的情况进行检查发现，合子早期有丝分裂存在不对称性，即当两条异源染色体在体细胞分裂时丢失，几乎总是一个子核没有得到任何一条，而另一个子核获得其正常的染色体组。推测这种不对称性不是pal的特性，而是该突变体揭示的一个正常过程。（6）pal雄性后代中染色体的体细胞丢失使得能够构建囊胚层的命运图谱。使用来自雌雄嵌合体和标记Y染色体（非性二态）嵌合体的数据可获得类似的命运图谱。
