Chromosome

About: Chromosome is a research topic. Over the lifetime, 17538 publications have been published within this topic receiving 660077 citations. The topic is also known as: chromosomes & GO:0005694.

Asymmetric regulation of imprinting on the maternal and paternal chromosomes at the Dlk1-Gtl2 imprinted cluster on mouse chromosome 12

Abstract: Genomic imprinting causes parental origin-specific gene expression. Cis-acting regulatory elements that control imprinting are not fully understood but involve regions that become differentially methylated on the two parental chromosomes during male and female gametogenesis. Understanding properties of maternally and paternally inherited imprints provides insight into the mechanisms and evolution of genomic imprinting. Previously we identified an intergenic germline-derived differentially methylated region (IG-DMR) that is a candidate control element for an imprinted domain on distal mouse chromosome 12 (ref. 5). The 1-Mb cluster contains the paternally expressed protein-coding genes Dlk1 (refs. 6,7) and Dio3 (ref. 8,9) and several maternally expressed non-coding RNAs, including Gtl2 (refs. 6,7,10) and C/D snoRNAs. A retrotransposon-like gene (Rtl1) is expressed from the paternal chromosome and has an antisense transcript expressed from the maternal chromosome containing two microRNAs with full complementarity to Rtl1 (ref. 12). Here we show that deletion of the IG-DMR from the maternally inherited chromosome causes bidirectional loss of imprinting of all genes in the cluster. When the deletion is transmitted from the father, imprinting is unaltered. These results prove that the IG-DMR is a control element for all imprinted genes on the maternal chromosome only and indicate that the two parental chromosomes control allele-specific gene expression differently.

Characterisation of the double genome structure of modern sugarcane cultivars (Saccharum spp.) by molecular cytogenetics.

Abstract: Cultivated sugarcane clones (Saccharum spp., 2n=100 to 130) are derived from complex interspecific hybridizations between the speciesS. officinarum andS. spontaneum. Using comparative genomic DNA in situ hybridization, we demonstrated that it is possible to distinguish the chromosomes contributed by these two species in an interspecific F1 hybrid and a cultivated clone, R570. In the interspecific F1 studied, we observed n+n transmission of the parental chromosomes instead of the peculiar 2n+n transmission usually described in such crosses. Among the chromosomes of cultivar R570 (2n=107–115) about 10% were identified as originating fromS. spontaneum and about 10% were identified as recombinant chromosomes between the two speciesS. officinarum andS. spontaneum. This demonstrated for the first time the occurrence of recombination between the chromosomes of these two species. The rDNA sites were located by in situ hybridization in these two species and the cultivar R570. This supported different basic chromosome numbers and chromosome structural differences between the two species and provided a first bridge between physical and genetical mapping in sugarcane.

Identification and High-Density Mapping of Gene-Rich Regions in Chromosome Group 1 of Wheat

Abstract: We studied the distribution of genes and recombination in wheat (Triticum aestivum) group 1 chromosomes by comparing high-density physical and genetic maps. Physical maps of chromosomes 1A, 1B, and 1D were generated by mapping 50 DNA markers on 56 single-break deletion lines. A consensus physical map was compared with the 1D genetic map of Triticum tauschii (68 markers) and a Triticeae group 1 consensus map (288 markers) to generate a cytogenetic ladder map (CLM). Most group 1 markers (86%) were present in five clusters that encompassed only 10% of the group 1 chromosome. This distribution may reflect that of genes because more than half of the probes were cDNA clones and 30% were PstI genomic. All 14 agronomically important genes in group 1 chromosomes were present in these clusters. Most recombination occurred in gene-cluster regions. Markers fell at an average distance of 244 kb in these regions. The CLM involving the Triticeae consensus genetic map revealed that the above distribution of genes and recombination is the same in other Triticeae species. Because of a significant number of common markers, our CLM can be used for comparative mapping and to estimate physical distances among markers in many Poaceae species including rice and maize.

Clustering of breakpoints on chromosome 11 in human B-cell neoplasms with the t(11;14) chromosome translocation.

Abstract: The t(11;14) (q13;q32) chromosome translocation has been reported in diffuse small and large cell lymphomas and in chronic lymphocytic leukaemia (B-CLL) and multiple myeloma. Because chromosome band 14q32 is involved in this translocation, as well as in the t(8;14) (q24;q32) translocation of the Burkitt tumour, interruption of the immunoglobulin heavy-chain locus was postulated for this rearrangement. We have cloned the chromosomal joinings between chromosomes 11 and 14 and also between chromosomes 14 and 18, in B-cell tumours carrying translocations involving these chromosomes, and suggested the existence of two translocated loci, bcl-1 and bcl-2, normally located on chromosomes 11 (band q13) and 18 (band q21) respectively, involved in the pathogenesis of human B-cell neoplasms. The results indicate that in the leukaemic cells from two different cases of CLL, the breakpoints on chromosome 11 are within 8 nucleotides of each other and on chromosome 14 involve the J4-DNA segment. Because we detected a 7mer-9mer signal-like sequence with a 12-base-long spacer on the normal chromosome 11, close to the breakpoint, we speculate that the t(11;14) chromosome translocation in CLL may be sequence specific and may involve the recombination system for immunoglobulin gene segment (V-D-J) joining.

Reptitive DNA sequences in drosophila.

Abstract: The satellite DNAs of Drosophila melanogaster and D. virilis have been examined by isopycnic centrifugation, thermal denaturation, and in situ molecular hybridization. The satellites melt over a narrow temperature range, reassociate rapidly after denaturation, and separate into strands of differing buoyant density in alkaline CsCl. In D. virilis and D. melanogaster the satellites constitute respectively 41% and 8% of the DNA isolated from diploid tissue. The satellites make up only a minute fraction of the DNA isolated from polytene tissue. Complementary RNA synthesized in vitro from the largest satellite of D. virilis hybridized to the centromeric heterochromatin of mitotic chromosomes, although binding to the Y chromosome was low. The same cRNA hybridized primarily to the α-heterochromatin in the chromocenter of salivary gland nuclei. The level of hybridization in diploid and polytene nuclei was similar, despite the great difference in total DNA content. The centrifugation and hybridization data imply that the α-heterochromatin either does not replicate or replicates only slightly during polytenization. Similar but less extensive data are presented for D. melanogaster. — In D. melanogaster cRNA synthesized from total DNA hybridized to the entire chromocenter (α- and β-heterochromatin) and less intensely to many bands on the chromosome arms. The X chromosome was more heavily labeled than the autosomes. In D. virilis the X chromosome showed a similar preferential binding of cRNA copied from main peak sequences.—It is concluded that the majority of repetitive sequences in D. virilis and D. melanogaster are located in the α- and β-heterochromatin. Repetitive sequences constitute only a small percentage of the euchromatin, but they are widely distributed in the chromosomes. During polytenization the α-heterochromatin probably does not replicate, but some or all of the repetitive sequences in the β-heterochromatin and the euchromatin do replicate.