Lee K H, Fechheimer N S, Abplanalp H
Department of Molecular Genetics, Ohio State University, Columbus 43210.
J Reprod Fertil. 1990 May;89(1):85-90. doi: 10.1530/jrf.0.0890085.
A high incidence of haploid/diploid chimerism in chick embryos from strains of chickens selected for large size was postulated to be caused by the propensity of such hens to ovulate erratically. To test the hypothesis karyological analysis was made of embryos in eggs containing 1 or greater than 1 yolk. The eggs were from a line selected for multiple ovulation for 20 generations. Double and multiple-yolk eggs are a manifestation of an irregular ovulatory pattern. Ova in multiple yolk eggs were significantly less fertile and significantly fewer embryos survived to 18 h of incubation than single ovulated ova. In the sample of 342 embryos analysed, only 2 forms of heteroploidy occurred in frequencies of greater than 1.2%; 2n/4n mosaicism (5.8%) and 3n (5.0%). Only triploidy occurred significantly more frequently in eggs containing greater than 1 yolk (7.0%) than in single yolk eggs (none). The overwhelming majority of 3n embryos had a digynic origin (i.e from ova with 2 maternal pronuclei), as inferred from the sex chromosome complement. Erratic ovulation therefore resulted in suppression of second polar body extrusion leading to digynic triploidy. Multiple yolks had no effect on dispermy, the primary cause of 1n/2n chimaeric embryos, in single-yolked chicken eggs.
据推测，为培育大体型鸡而选择的品系所产鸡胚中，单倍体/二倍体嵌合体的高发生率是由这类母鸡排卵不规律的倾向所致。为验证这一假说，对含有1个或1个以上卵黄的鸡蛋中的胚胎进行了核型分析。这些鸡蛋来自一个经20代选育具有多次排卵特性的品系。双黄蛋和多黄蛋是排卵模式不规则的一种表现。与单排卵的卵子相比，多黄蛋中的卵子受精率显著降低，孵化至18小时存活的胚胎数量也显著减少。在分析的342个胚胎样本中，仅出现了两种频率高于1.2%的异倍体形式；2n/4n嵌合体（5.8%）和3n（5.0%）。只有三倍体在含有1个以上卵黄的鸡蛋中出现的频率（7.0%）显著高于单黄蛋（未出现）。从性染色体组成推断，绝大多数3n胚胎起源于双雌核（即来自具有2个母源原核的卵子）。因此，排卵不规律导致第二极体排出受阻，进而产生双雌核三倍体。多卵黄对单黄鸡蛋中1n/2n嵌合胚胎的主要成因——双精受精没有影响。
