The discrepancies likely were generated either by differences in the methylation status at NotI sites between the twins or by submicroscopic changes occurring at NotI-flanking sites in one twin after (or simultaneous with) twinning. In either case, the difference may influence the transcription level of one or more genes.
The origin of the domestic fowl and its relationship to the jungle fowl is a continuing interest to the scientists working with poultry. The present study was conducted in order to clarify the relationships among the domestic and jungle fowls using DNA fingerprinting (DFP). These DFP analyses were carried out by mixing equal amounts of DNA from several individuals of a particular population, resulting in a DFP parttern characteristic of the population. Similarities of DFP pattern between breeds or species of fowl were estimated using band sharing (BS) value. From the BS values, the Japanese native stocks and Chinese native stocks were found to form two separate groups, respectively. BS values between Green Jungle Fowl and all other stocks were generally low. Genetic distance among the domestic and jungle fowls was estimated as the mean number of nucleotide substitutions per nucleotide site. The results indicated that Red Jungle Fowl was relatively close to the domestic fowls. On the other hand, Green Jungle Fowl was found to be related most remotely to the domestic fowls. Thus, DFP analysis with mixed DNA could be effectively used to assess the genetic relationship among the stocks of fowls.
To understand the effect of trisomic chromosome 21 on the cause of Down syndrome (DS), DNA methylation in the CpG island, which regulates the expression of adjacent genes, was investigated with the DNAs of chromosome 21 isolated from DS patients and their parents. A methylation-sensitive enzyme, BssHII, was used to digest DNAs of chromosome 21, and the resulting DNA fragments were subjected to RLGS (restriction landmark genomic scanning). Surprisingly, the CpG island of the h2-calponin gene was shown to be specifically methylated by comparative studies with RLGS and Southern blot analysis. In association with this methylation, h2-calponin gene expression was attenuated to the normal level, although other genes in the DS region of chromosome 21 were expressed dose dependently at 1.5 times the normal level. These results and the high miscarriage rate associated with trisomy 21 embryos imply that the altered in vivo methylation that attenuates downstream gene expression, which is otherwise lethal, permits the generation of DS neonates. The h2-calponin gene detected by the RLGS procedure may be one such gene that is attenuated.
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