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.

Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution

Abstract: Sex chromosomes originate from autosomes. The accumulation of sexually antagonistic mutations on protosex chromosomes selects for a loss of recombination and sets in motion the evolutionary processes generating heteromorphic sex chromosomes. Recombination suppression and differentiation are generally viewed as the default path of sex chromosome evolution, and the occurrence of old, homomorphic sex chromosomes, such as those of ratite birds, has remained a mystery. Here, we analyze the genome and transcriptome of emu (Dromaius novaehollandiae) and confirm that most genes on the sex chromosome are shared between the Z and W. Surprisingly, however, levels of gene expression are generally sex-biased for all sex-linked genes relative to autosomes, including those in the pseudoautosomal region, and the male-bias increases after gonad formation. This expression bias suggests that the emu sex chromosomes have become masculinized, even in the absence of ZW differentiation. Thus, birds may have taken different evolutionary solutions to minimize the deleterious effects imposed by sexually antagonistic mutations: some lineages eliminate recombination along the protosex chromosomes to physically restrict sexually antagonistic alleles to one sex, whereas ratites evolved sex-biased expression to confine the product of a sexually antagonistic allele to the sex it benefits. This difference in conflict resolution may explain the preservation of recombining, homomorphic sex chromosomes in other lineages and illustrates the importance of sexually antagonistic mutations driving the evolution of sex chromosomes.

The timing of chromosome elimination in hexaploid wheat × maize crosses

Abstract: Early seed development in crosses between the hexaploid wheat genotype 'Chinese Spring' and the maize genotype 'Seneca 60' was studied to determine the timing of elimination of the maize chromosomes. Elimination of one or more maize chromosomes occurred in about 70% of zygotic mitoses. Metaphase nuclei from two-celled embryos had 5 to 10 maize chromosomes, most of which were lost during the second cell division. About half the metaphase nuclei from four-celled embryos had no maize chromosomes, and the remainder had one to five. Anaphase or telophase nuclei from four-celled embryos showed no maize chromosomes in about half the cells and one or more pairs of lagging maize daughter chromosomes in the remainder. No maize chromosomes were seen in metaphase preparations from embryos with eight or more cells. These data strongly suggest that all maize chromosomes were lost during the first three cell-division cycles in most embryos. All embryos with four or more cells had micronuclei, showing that embryo develop...

Evidence for Subtelomeric Exchange of 3.3 kb Tandemly Repeated Units between Chromosomes 4q35 and 10q26: Implications for Genetic Counselling and Etiology of FSHD1

Abstract: Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant myopathy, clinically characterized by asymmetric weakness of muscles in the face, shoulder girdle and upper arm. Deletion of an integral number of 3.3 kb repeated units within a highly polymorphic EcoRI fragment at chromosome 4q35, generating a relatively short EcoRI fragment (< 35 kb), has been shown to cause FSHD1. Probe p13E-11 detects these short fragments in FSHD1 patients, and has therefore been used for diagnostic DNA analysis. However, the reliability of this analysis has been hampered by cross-hybridization of p13E-11 to chromosome 10q26-linked EcoRI fragments of comparable size, which also contain a variable number of 3.3 kb repeated units. Recently, a BinI restriction site was identified within each of the repeated units derived from chromosome 10q26, which enables differentiation of the two polymorphic p13E-11 loci in most cases without haplotype analysis. Remarkably, applying the differential analysis to screen DNA of 160 Dutch cases referred to us for FSHD1 diagnosis, we obtained evidence for subtelomeric exchange of 3.3 kb repeated units between chromosomes 4q35 and 10q26 in affected and unaffected individuals. Subsequently, analysis of 50 unrelated control samples indicated such exchange between chromosomes 4q35 and 10q26 in at least 20% of the population. These subtelomeric rearrangements have generated a novel interchromosomal polymorphism, which has implications for the specificity and sensitivity of the differential restriction analysis for diagnostic purposes. Moreover, the high frequency of the interchromosomal exchanges of 3.3 kb repeated units suggests that they probably do not contain (part of) the FSHD1 gene, and supports position effect variegation as the most likely mechanism for FSHD1.

Molecular cytogenetic delineation of a novel critical genomic region in chromosome bands 11q22.3-923.1 in lymphoproliferative disorders.

Abstract: Aberrations of the long arm of chromosome 11 are among the most common chromosome abnormalities in lymphoproliferative disorders (LPD). Translocations involving BCL1 at 11q13 are strongly associated with mantle cell lymphoma. other nonrandom aberrations, especially deletions and, less frequently, translocations, involving bands 11q21-923 have been identified by chromosome banding analysis. To date, the critical genomic segment and candidate genes involved in these deletions have not been identified. In the present study, we have analyzed tumors from 43 patients with LPD (B-cell chronic lymphocytic leukemia, n = 40; mantle cell lymphoma, n = 3) showing aberrations of bands 11q21-923 by fluorescence in situ hybridization. As probes we used Alu-PCR products from 17 yeast artificial chromosome clones spanning chromosome bands 11q14.3-923.3, including a panel of yeast artificial chromosome clones recognizing a contiguous genomic DNA fragment of approximately 9-10 Mb in bands 11q22.3-923.3. In the 41 tumors exhibiting deletions, we identified a commonly deleted segment in band 11q22.3-923.1; this region is approximately 2-3 Mb in size and contains the genes coding for ATM (ataxia telangiectasia mutated), RDX (radixin), and FDX1 (ferredoxin 1). Furthermore, two translocation break-points were localized to a 1.8-Mb genomic fragment contained within the commonly deleted segment. Thus, we have identified a single critical region of 2-3 Mb in size in which 11q14-923 aberrations in LPD cluster. This provides the basis for the identification of the gene(s) at 11q22.3-923.1 that are involved in the pathogenesis of LPD.

Distal deletion of chromosome Ip in ductal carcinoma of the breast.

Abstract: By use of recombinant DNA probes that correspond to genetic loci residing on human chromosome 1, DNA samples from 37 ductal breast carcinomas and constitutional DNA from the same individuals were tested for loss of heterozygosity A high frequency (41%) of reduction to homozygosity was detected with the probe p1-79, which recognizes the highly polymorphic locus D1Z2, localized on 1p36 Loss of heterozygosity at other chromosome 1 loci was much less common, not exceeding a frequency of 10%, and was never observed in the absence of the D1Z2 loss Somatic loss of heterozygosity at D1Z2 was more frequent in patients with a strong family history of breast cancer (60%), in patients with early diagnosis (before 45 years of age) (70%), and in those with multiple tumors or tumor foci (50%) than in patients with none of the characteristics of hereditary tumors (21%) No associations were observed between loss of heterozygosity and prognostic factors These results suggest that inactivation of a tumor suppressor gene located on the distal portion of chromosome 1p, alone or combined with other genetic changes, may represent a fundamental step in the pathogenesis of ductal carcinoma of the breast