Nur U
Department of Biology, University of Rochester, NY 14627.
Dev Suppl. 1990:29-34.
In several families of scale insects (coccids), the sex of an embryo is determined by the number of genetically active genomes present (one = males, two = females). In mealybugs (Pseudococcidae), both males and females develop from fertilized eggs but, in the embryos that develop into males, the set of chromosomes (genome) of paternal origin (PG) becomes heterochromatic (H) and genetically inactive and is not transmitted to the offspring. The mechanism that reduces the number of active genomes in male embryos may vary between families and even between congeneric species. Thus, in male embryos of most armored scale species (Diaspididae), the PG is eliminated, while in a few species it becomes H. In two genera of soft scales (Coccidae), males develop from unfertilized eggs when one of two identical genomes of maternal origin becomes H. In most male tissues, one genome remains H. However, in several tissues that become polyploid by endoreduplication, the PG becomes E and genetically active. The tissues in which the PG becomes E often vary between species and the analysis of hybrid males demonstrated that whether the PG becomes H or remains E is determined by the genome of maternal origin. The euchromatization of the PG in the haploid sector of mosaic male embryos and the presence of spermatocytes with two E genomes (instead of one E and one H), following the irradiation of young mealybug males, strongly suggest that the maintenance of the H state requires the presence of a genetically active genome.
在几个蚧虫科（球蚧）中，胚胎的性别由存在的基因活性基因组数量决定（一个 = 雄性，两个 = 雌性）。在粉蚧（粉蚧科）中，雄性和雌性均由受精卵发育而来，但在发育成雄性的胚胎中，父本来源的染色体组（基因组）（PG）会变成异染色质（H）且基因失活，并且不会传递给后代。减少雄性胚胎中活性基因组数量的机制可能因科甚至同属物种而异。因此，在大多数盾蚧科物种的雄性胚胎中，PG会被消除，而在少数物种中它会变成H。在绵蚧科的两个属中，当母本来源的两个相同基因组之一变成H时，雄性由未受精卵发育而来。在大多数雄性组织中，一个基因组保持为H。然而，在通过核内复制变成多倍体的几个组织中，PG会变成E且基因活跃。PG变成E的组织通常因物种而异，对杂交雄性的分析表明，PG是变成H还是保持为E由母本来源的基因组决定。在镶嵌雄性胚胎的单倍体区域中PG的常染色质化，以及对年轻粉蚧雄性进行辐射后出现具有两个E基因组（而非一个E和一个H）的精母细胞，强烈表明H状态的维持需要存在一个基因活跃的基因组。
