Mechanisms involved in the spontaneous occurrence of diploid-triploid chimerism in the mink <i>(Mustela viso</i><i>n</i>) and chicken (<i>Gallus domesticu</i><i>s</i>)

Abstract

Diploid-triploid chimeras have been observed both in man and in a number of laboratory and livestock animals. The mechanism(s) of their origin remains enigmatic. One approach is to calculate for each proposed mechanism the expected frequencies of zygotes bearing different gonosomic complements in the two cell lines. Observed samples are then compared with the expectations. The mechanisms that have been considered include: (1) fertilization of a blastomere, (2) absorption of the second polar body into a blastomere, (3) fertilization of the first polar body, (4) independent fertilization of both nuclei in binucleated oocytes, (5) fertilization of the second polar body as well as the egg, and (6) fusion of two eggs. The sample of minks comprised three preimplantation embryos, nine postimplantation embryos, and three neonatal pups, with gonosomic complements of 7 XX/XXX, 3 XX/XXY, 4XY/XXY, and 1 XY/XYY; the chicks comprised 13 embryos at 1 day of incubation, 1 embryo at 4 days, and one adult bird, with gonosomic complements of 5 ZZ/ZZZ, 1 ZZ/ZZW, 1 ZW/ZZZ, 3 ZW/ZZW, and 5 ZW/ZWW. If it is assumed that within each species all, or most, of the 2n/3n chimeras arise from the same mechanism, then the occurrence of a type that has an expected frequency of zero for a given proposed mechanism effectively eliminates that mechanism as a source. All of the chicks could have resulted from only one mechanism, viz., independent fertilization of both nuclei in binucleated oocytes. The sample of minks could have resulted from the same mechanism or from fertilization of a blastomere of a two-cell, 2n embryo.

Cell death in the avian blastoderm: resistance to stress-induced apoptosis and expression of anti-apoptotic genes

“…A variety of cytogenetic abnormalities in the early chick embryo have been observed previously including aneuploidy, haploidy, and polyploidy (Bloom, 1972). Also, many embryos are mosaics and chimeras (Fechheimer et al, 1983;Bloom, 1972). Such embryos are usually arrested in early development, and perhaps this is due to excessive cell deaths.…”

Diploid-Triploid Mosaicism and Tissue Ploidy Diversity within <i>Platemys platycephala</i> from Suriname

“…Both the frequencies of mosaicism and the male cytogenetics data are convincing that diploid-triploid mosaicism represents a normal component of the genetic system of this species. This is remarkable given the fact that diploid-triploid mosaicism is a well-known constitutional chromosome disorder that has been well studied in man, mink and chickens [Fechheimer, 1981;Graham et al, 1981;Fechheimer et al, 1983].…”

“…Diploid-triploid mosaicism is known to occur spontaneously in a variety of species including man and several other species of mammals, chicken, fish, and lizards [Bezy, 1972;Fechheimer et al, 1983;Lampert et al, 2007], but in these cases the mosaicism represents a birth defect rather than a normal condition of the species. They are typically sterile and often unviable.…”

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“…Fechheimer et al (1983) review the possible mechanisms involved in the origin of diploid-triploid chimeras from typical bisexual species. Unisexual hybrids, however, present a special case, and the following two hypotheses represent the most likely explanations for the origin of mosaic Phoxinus.…”