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.

Genetic Variation in Chromosome Pairing

Abstract: Publisher Summary This chapter discusses the genetic variation in chromosome pairing Alterations in the behavior of chromosomes at meiosis are known to result from genetic variation as well as from differences in several environmental factors The operation of selection on genetically controlled variation in the chromosomal phenotype is responsible for the development of meiotic mechanisms adapted to the requirements of the breeding structures of species and of their populations The fertility of an organism and consequently the fitness of the lineage to which it belongs are intimately related in sexual forms and in some apomicts, to the efficiency of the over-all meiotic process The prime function, upon which the efficacy of the process depends, is the segregation of homologous chromosomes Two distinct aspects of the process of meiotic chromosome pairing are therefore under genetic control The extent to which synapsis is realized within the chromosome complement is determined by the activities of major genes and polygenes and by interactions within the genetic system comprised of relevant genes of both kinds The specificity of synapsis is widened or narrowed by gene action to permit the pairing of chromosomes distantly or closely related genetically and evolutionarily

Arm homoeology of wheat and rye chromosomes

Abstract: Meiotic pairing was studied at metaphase I in three different cv. Chinese Spring × rye hybrid combinations (5B deficient, 3D deficient, and normal ABDR) to establish the arm homoeology of wheat and rye chromosomes. The majority of individual wheat chromosomes and their arms, as well as the arms of chromosomes 1R and 5R, were identified by means of C-banding. The results on pairing relationships support the genome reallocation of chromosomes 4A and 4B. The short arms of wheat chromosomes belonging to homoeologous groups 1, 3, 5, and 6 and of chromosome pairs 4A–4D and 7A–7D showed full pairing homoeology as well as the long arms of wheat chromosomes of groups 1, 3, 6, and 7 and of chromosome pairs 4A–4D and 5B–5D. Chromosomes 2A, 2B, and 2D were homoeologous, but the homoeologies of their arms were not identified. Reduced homoeologies of the 4BL arm to 7AS and 7DS, of the 5AL arm to 4AL and 4DL, and of the 7BS arm to 5BL and 5DL were identified. Arms 4BL, 5AL, and 7BS are involved in a double translocation...

Genomes, genes and junk: the large-scale organization of plant chromosomes

Abstract: Plants from wide taxonomic groupings have similar genes and ordering of genes along the chromosomes. However, the repetitive DNA, much of no known function and often constituting the majority of the genome, varies extensively from species to species in absolute amount, sequence and dispersion pattern. Despite this, it is known that families of repeated DNA motifs each have a characteristic genomic location within a genus, and that there are different constraints on the evolution of repetitive DNA and genes. There are now enough data about different types of repetitive DNA—from sequencing, Southern analysis and in situ hybridization—to build a model of the organization of a typical plant genome, and apply it to gene cloning, evolutionary studies and gene transfer.

Hypomethylation of pericentromeric DNA in breast adenocarcinomas

Abstract: Drug-induced DNA demethylation in normal human cells and inherited localized hypomethylation in mitogen-stimulated lymphocytes from patients with a rare recessive disease (ICF: immunodeficiency, centromeric region instability, facial anomalies) are associated with karyotypic instability. This chromosomal recombination is targeted to heterochromatin in the vicinity of the centromere (pericentromeric region) of human chromosome 1. Pericentromeric rearrangements in this chromosome as well as overall genomic hypomethylation are frequently observed in many kinds of cancer, including breast adenocarcinoma. We found that almost half of 25 examined breast adenocarcinomas exhibited hypomethylation in satellite 2 DNA, which is located in the long region of heterochromatin adjacent to the centromere of chromosome 1 and is normally highly methylated. One of the 19 examined non-malignant breast tissues displaying fibrocystic changes was similarly hypomethylated in this satellite DNA. We also looked at an opposing type of methylation alteration in these cancers, namely, hypermethylation in a tumorsuppressor gene region that is frequently hypermethylated in breast cancers. We found that increased methylation in the E-cadherin promoter region and decreased methylation in satellite 2 DNA were often present in the same breast cancers. While hypermethylation in certain tumor-suppressor gene regions may favor tumorigenesis by repressing transcription, demethylation of other DNA sequences may predispose to cancer-promoting chromosomal re-arrangements. Int. J. Cancer 77:833‐838, 1998. r 1998 Wiley-Liss, Inc.