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.

The evolutionary history of Drosophila buzzatii IX. High frequencies of new chromosome rearrangements induced by introgressive hybridization

Abstract: Introgression of a chromosome segment from Drosophila serido into the genome of its sibling D. buzzatii brought about the release of mutator potential in the hybrids. Mutator activity was determined by examining the frequency of new chromosomal rearrangements, that appeared only in the progeny of hybrid individuals. Mutation frequency was 30 times greater in the progeny of hybrid males than in that of hybrid females. There was a remarkable influence of the D. buzzatii genetic background on the frequency of production of these new rearrangements. The appearance of a new rearrangement did not depend on the genotype of the larva that bore it, but only on that of its hybrid progenitor. Among the new rearrangements there were inversions, translocations, and duplications. The number of translocations was significantly lower than that of inversions or duplications; this last type was the most frequently recorded. The distribution of the aberrations among the four major autosomes seemed to be homogeneous, although the total number of breakpoints was significantly greater in chromosome 4 than in the others. No rearrangement was found on the X chromosome. Breakpoints within three of the four affected autosomes were not randomly distributed.

Genetics of mammalian sex chromosomes.

Abstract: The great strides made during the past two years in the whole field of mammalian cytogenetics have, in particular, enlarged our knowledge of the role of the mammalian sex chromosomes. The following summary briefly lists the most recent discoveries in the mouse, where genetic findings have played a relatively greater role than in the other species of mammals. The male-determining property of the mammalian Y chromosome, established earlier in mouse and man, has been further confirmed by the finding of an XXY mouse, which was detected by genetic means and has been studied cytologically. This animal is a fully viable, phenotypically normal, though sterile, male. Since various doubts concerning detectability of the XXY type have been removed by the discovery of this animal, it can be concluded that the occurrence of XXY in the mouse is extremely rare. It has been shown that the X chromosome of the mouse, when it is involved in certain chromosomal rearrangements, has the power to produce variegated-type position effects, a phenomenon formerly not observed in any animal except Drosophila. The fact that the X chromosome is involved in all four of the known cases of V-type position effect in the mouse indicates that it is strongly heterochromatic, while there may be little heterochromatin on the autosomes. Recent findings have shown that the presence of two X chromosomes is necessary for the expression of the position effect in one of them. This fact, when related to various cytological findings in other species, permits the hypothesis that, in mammals, genic balance requires the action of one X in a manner which precludes realization of its heterochromatic potentialities, so that only any additional X's present assume the properties characteristic of heterochromatin. A variety of different findings sheds light on the mechanisms that may lead to the occurrence of individuals with abnormal numbers of sex chromosomes. The XXY mouse proves, by virtue of its sex-linked marker genes, that nondisjunction can occur in the first meiotic division of a normal male (a proof not previously provided by human cases of XXY, which could have been of different origin). However, first-meiotic nondisjunction is apparently very rare in males, and there is not yet any evidence that it ever occurs in females. Data from numerous types of crosses involving five sex-linked markers yield the following results: no cases of X(M)X(M)Y or OX(P) have occurred to date; X(M)X(P)Y << X(M)O; OX(P) << X(M)O (where the superscripts M and P designate maternal and paternal derivation, respectively, of the X). The total frequency of XO individuals can be increased by irradiation shortly after fertilization. This treatment has yielded, in addition to X(M)O, several animals of the OX(P) constitution, a type that has not yet been found to occur spontaneously. The various findings on spontaneous and induced frequencies of mice with abnormal numbers of sex chromosomes lead to the conclusion that XO individuals are most often the result of events occurring after fertilization. Specifically, it is suggested that there exists a relatively high probability of loss of the paternally contributed sex chromosome some time between fertilization and the first cleavage(32).

B-Chromosome Systems in Flowering Plants and Animal Species

Abstract: Publisher Summary This chapter discusses the B-chromosome systems in flowering plants and animal species. The term B chromosome is introduced to describe extra chromosome which have little if any effect on visible characters of the plant, which are not homologous with the A chromosomes of the normal complement, and which are extremely irregular in their meiotic distribution. B Chromosomes are now known under a variety of different names, including supernumerary and accessory, which are the most common alternatives. B chromosomes are dispensable and nonhomologous with A chromosomes. These two characteristics above all others most sharply differentiate them from members of the basic A-chromosome complement. The distribution of B chromosome in plant and animal species is discussed. In many plants and animals the B chromosomes are completely stable during the cell cycle and are inherited in a constant and unchanging form along with the A chromosomes. Some plant species have an apparent order in their instability, which results in exclusion and/or accumulation of B chromosomes in specific tissues and organs. The significance of B-chromosome effects in flowering plants and animals is discussed.

A chromosome region-specific mapping strategy reveals gene-rich telomeric ends in wheat

Abstract: A strategy is described for rapid chromosome region-specific mapping in hexaploid wheat (Triticum aestivum L. em. Thell., 2n=6x=42, AABBDD). The method involves allocation of markers to specific chromosome regions by deletion mapping and ordering of probes by high resolution genetic mapping in Triticum tauschii, the D-genome progenitor species. The strategy is demonstrated using 26 chromosome deletion lines for wheat homoeologous group-6. Twenty-five DNA probes from the T. tauschii genetic linkage map and six wheat homoeologous group-6 specific probes were mapped on the deletion lines. Twenty-four of the 25 probes from 6D of T. tauschii also mapped on wheat homoeologous group-6 chromosomes, and their linear order in wheat is the same as in T. tauschii. A consensus physical map of wheat group-6 was constructed because the linear order and the relative position of the probe loci was the same among the three group-6 chromosomes. Comparison of the consensus physical map with the genetic map demonstrated that most of the recombination occurs in the distal ends of the wheat chromosomes. Most of the loci mapped in the distal regions of the chromosomes. The probes were mostly either PstI genomic clones or cDNA clones indicating that the undermethylated single-copy sequences are concentrated in the distal ends of the wheat chromosomes. Fifteen loci are uniformly distributed in the distal 11% of the group-6 chromosomes. Physically, the region spans only 0.58 μm, which in wheat translates to about 40 Mb of DNA. The average distance between the markers is, therefore, less than 2.7 Mb and is in the range of PFGE (pulsed-field gel electrophoresis) resolution. Any gene present in the region can be genetically ordered with respect to the markers since the average recombination frequency in the region is very high (>90 cM genetic distance).