scholarly journals A MODEL OF DUPLICATIVE TRANSPOSITION AND GENE CONVERSION FOR REPETITIVE DNA FAMILIES

Genetics ◽  
1985 ◽  
Vol 110 (3) ◽  
pp. 513-524
Author(s):  
Tomoko Ohta
Keyword(s):  
Gene Conversion ◽  
Repetitive Dna ◽  
Repetitive Sequences ◽  
Diploid Cell ◽  
Multigene Families ◽  
Numerical Studies

ABSTRACT A model of duplicative transposition and gene conversion for the evolution of repetitive DNA families was studied. In this model, transposition and conversion (both unbiased) are assumed to occur both within and between the genomes in a diploid cell, and any degree of linkage intensity is incorporated. The transition equations for allelic and nonallelic identity coefficients have been formulated by using the previous results. The results are widely applicable to many repetitive sequences, from dispersed families like transposons to tightly linked multigene families. It has been shown through extensive numerical studies on equilibrium properties that duplicative transposition and gene conversion have very similar effects on nonallelic identity coefficients, but that allelism and allelic identity are greatly influenced by the relative rates of occurrence of the two processes.

Neutral mutations and repetitive DNA

1987 ◽  
Vol 7 (7) ◽  
pp. 599-606 ◽  
Author(s):  
William F. Loomis ◽  
Michael E. Gilpin
Keyword(s):  
Dna Sequence ◽  
Computer Simulations ◽  
Repetitive Dna ◽  
Repetitive Sequences ◽  
Multigene Families ◽  
Neutral Mutations ◽  
Evolution Of Genomes

We have previously shown that computer simulations of processes that generate selectively advantageous changes together with random duplications and deletions give rise to genomes with many different genes embedded in a large amount of dispensable DNA sequence. We now explore the consequences of neutral changes on the evolution of genomes. We follow the consequences of sequence divergences that are neutral when they occur in dispensable sequences or extra copies of genes present in multigene families. We find that when divergence occurs at about the same frequency as duplication/deletion events, genomes carry repetitive sequences in proportion to their size. Inspection of the genomes as they evolved showed that multigene families were generated by relatively recent duplications of single genes and so would be expected to be highly homogeneous.

scholarly journals Sequence identity in an early chorion multigene family is the result of localized gene conversion.

Genetics ◽  
1991 ◽  
Vol 128 (3) ◽  
pp. 595-606
Author(s):  
B L Hibner ◽  
W D Burke ◽  
T H Eickbush
Keyword(s):  
Nucleotide Sequence ◽  
Gene Conversion ◽  
Nucleotide Sequence Identity ◽  
Early Period ◽  
Gene Families ◽  
Multigene Families ◽  
Coding Regions ◽  
Sequence Identity ◽  
Isolation And Characterization ◽  
Sequence Exchange

Abstract The multigene families that encode the chorion (eggshell) of the silk moth, Bombyx mori, are closely linked on one chromosome. We report here the isolation and characterization of two segments, totaling 102 kb of genomic DNA, containing the genes expressed during the early period of choriogenesis. Most of these early genes can be divided into two multigene families, ErA and ErB, organized into five divergently transcribed ErA/ErB gene pairs. Nucleotide sequence identity in the major coding regions of the ErA genes was 96%, while nucleotide sequence identity for the ErB major coding regions was only 63%. Selection pressure on the encoded proteins cannot explain this difference in the level of sequence conservation between the ErA and ErB gene families, since when only fourfold redundant codon positions are considered, the divergence within the ErA genes is 8%, while the divergence within the ErB genes (corrected for multiple substitutions at the same site) is 110%. The high sequence identity of the ErA major exons can be explained by sequence exchange events similar to gene conversion localized to the major exon of the ErA genes. These gene conversions are correlated with the presence of clustered copies of the nucleotide sequence GGXGGX, encoding paired glycine residues. This sequence has previously been correlated with gradients of gene conversion that extend throughout the coding and noncoding regions of the High-cysteine (Hc) chorion genes of B. mori. We suggest that the difference in the extent of the conversion tracts in these gene families reflects a tendency for these recombination events to become localized over time to the protein encoding regions of the major exons.

Distribution of the number of alleles in multigene families

1992 ◽  
Vol 29 (04) ◽  
pp. 759-769
Author(s):  
R. C. Griffiths
Keyword(s):  
Stochastic Model ◽  
Gene Conversion ◽  
Lower Bounds ◽  
Multigene Families ◽  
Expected Number ◽  
Allele Type ◽  
The Mean

The distribution of the number of alleles in samples from r chromosomes is studied. The stochastic model used includes gene conversion within chromosomes and mutation at loci on the chromosomes. A method is described for simulating the distribution of alleles and an algorithm given for computing lower bounds for the mean number of alleles. A formula is derived for the expected number of samples from r chromosomes which contain the allele type of a locus chosen at random.

scholarly journals Structures and stability of simple DNA repeats from bacteria

2020 ◽  
Vol 477 (2) ◽  
pp. 325-339 ◽  
Author(s):  
Vaclav Brazda ◽  
Miroslav Fojta ◽  
Richard P. Bowater
Keyword(s):  
Repetitive Dna ◽  
Dna Sequences ◽  
Genetic Instability ◽  
Repetitive Sequences ◽  
Biological Significance ◽  
Human Diseases ◽  
Repetitive Dna Sequences ◽  
Dna Repeats ◽  
Diverse Range ◽  
Dna Structures

DNA is a fundamentally important molecule for all cellular organisms due to its biological role as the store of hereditary, genetic information. On the one hand, genomic DNA is very stable, both in chemical and biological contexts, and this assists its genetic functions. On the other hand, it is also a dynamic molecule, and constant changes in its structure and sequence drive many biological processes, including adaptation and evolution of organisms. DNA genomes contain significant amounts of repetitive sequences, which have divergent functions in the complex processes that involve DNA, including replication, recombination, repair, and transcription. Through their involvement in these processes, repetitive DNA sequences influence the genetic instability and evolution of DNA molecules and they are located non-randomly in all genomes. Mechanisms that influence such genetic instability have been studied in many organisms, including within human genomes where they are linked to various human diseases. Here, we review our understanding of short, simple DNA repeats across a diverse range of bacteria, comparing the prevalence of repetitive DNA sequences in different genomes. We describe the range of DNA structures that have been observed in such repeats, focusing on their propensity to form local, non-B-DNA structures. Finally, we discuss the biological significance of such unusual DNA structures and relate this to studies where the impacts of DNA metabolism on genetic stability are linked to human diseases. Overall, we show that simple DNA repeats in bacteria serve as excellent and tractable experimental models for biochemical studies of their cellular functions and influences.

Cloning and characterization of repetitive DNA sequences from genomes of Oryza minuta and Oryza australiensis

Genome ◽  
1991 ◽  
Vol 34 (5) ◽  
pp. 790-798 ◽  
Author(s):  
H. Aswidinnoor ◽  
R. J. Nelson ◽  
J. F. Dallas ◽  
C. L. McIntyre ◽  
H. Leung ◽  
...  
Keyword(s):  
Repetitive Dna ◽  
Dna Sequences ◽  
Genomic Dna ◽  
Repetitive Sequences ◽  
Rice Genome ◽  
Repetitive Dna Sequences ◽  
Cross Hybridization ◽  
Oryza Minuta ◽  
Wild Rice Species ◽  
Oryza Australiensis

The value of genome-specific repetitive DNA sequences for use as molecular markers in studying genome differentiation was investigated. Five repetitive DNA sequences from wild species of rice were cloned. Four of the clones, pOm1, pOm4, pOmA536, and pOmPB10, were isolated from Oryza minuta accession 101141 (BBCC genomes), and one clone, pOa237, was isolated from Oryza australiensis accession 100882 (EE genome). Southern blot hybridization to different rice genomes showed strong hybridization of all five clones to O. minuta genomic DNA and no cross hybridization to genomic DNA from Oryza sativa (AA genome). The pOm1 and pOmA536 sequences showed cross hybridization only to all of the wild rice species containing the C genome. However, the pOm4, pOmPB10, and pOa237 sequences showed cross hybridization to O. australiensis genomic DNA in addition to showing hybridization to the O. minuta genomic DNA.Key words: rice, genome-specific repetitive sequences, Oryza.

Organization of the micronuclear genome of oxytricha nova.

Genetics ◽  
1988 ◽  
Vol 120 (1) ◽  
pp. 123-134
Author(s):  
C L Jahn ◽  
K E Prescott ◽  
M W Waggener
Keyword(s):  
Repetitive Dna ◽  
Repetitive Sequence ◽  
Repetitive Element ◽  
Repetitive Sequences ◽  
Unique Sequence ◽  
Sequence Family ◽  
Consensus Map ◽  
Ciliated Protozoan ◽  
Oxytricha Nova ◽  
First Time

Abstract In the hypotrichous ciliated protozoan Oxytricha nova, approximately 95% of the micronuclear genome, including all of the repetitive DNA and most of the unique sequence DNA, is eliminated during the formation of the macronuclear genome. We have examined the interspersion patterns of repetitive and unique and eliminated and retained sequences in the micronuclear genome by characterizing randomly selected clones of micronuclear DNA. Three major classes of clones have been defined: (1) those containing primarily unique, retained sequences; (2) those containing only unique, eliminated sequences; and (3) those containing only repetitive, eliminated sequences. Clones of type one and three document two aspects of organization observed previously: clustering of macronuclear destined sequences and the presence of a prevalent repetitive element. Clones of the second type demonstrate for the first time that eliminated unique sequence DNA occurs in long stretches uninterrupted by repetitive sequences. To further examine repetitive sequence interspersion, we characterized the repetitive sequence family that is present in 50% of the clones (class three above). A consensus map of this element was obtained by mapping approximately 80 phage clones and by hybridization to digests of micronuclear DNA. The repeat element is extremely large (approximately 24 kb) and is interspersed with both macronuclear destined sequences and eliminated unique sequences.

The mean number of alleles in multigene families

1992 ◽  
Vol 24 (01) ◽  
pp. 1-19 ◽  
Author(s):  
G. A. Watterson
Keyword(s):  
Probability Distribution ◽  
Gene Conversion ◽  
Random Sample ◽  
Multigene Families ◽  
Explicit Formulas ◽  
Large Samples ◽  
The Mean

The paper considers a random sample of r chromosomes, each having n genes subject to intrachromosomal gene conversion, and mutation. The probability distribution and moments for the number of alleles present is investigated, when the number, k, of possible alleles at each locus, is either finite or infinite. Explicit formulas are given for the mean numbers of alleles on r = 1, 2, or 3 chromosomes, which simplify previously known results. For fixed r, in the infinitely-many-alleles case, the mean number increases asymptotically like r θ log (n) as n→∞, where θ is a mutation parameter. But results for large samples remain elusive.

scholarly journals The evolutionarily conserved repetitive sequence d(TG.AC)n promotes reciprocal exchange and generates unusual recombinant tetrads during yeast meiosis.

1986 ◽  
Vol 6 (11) ◽  
pp. 3934-3947 ◽  
Author(s):  
D Treco ◽  
N Arnheim
Keyword(s):  
Gene Conversion ◽  
Repetitive Dna ◽  
Small Region ◽  
Marker Genes ◽  
Molecular Evidence ◽  
Yeast Saccharomyces Cerevisiae ◽  
Alternating Copolymer ◽  
Yeast Meiosis ◽  
Diploid Cells ◽  
Multiple Recombination

We have studied the genetic behavior of the alternating copolymer d(TG.AC)n inserted into a defined position in the genome of the yeast Saccharomyces cerevisiae. When d(TG.AC)n sequences were present at the HIS3 locus on homologous chromosomes, diploid cells undergoing meiosis generated an excess of tetrads containing reciprocally recombined products with crossover points close to the repetitive DNA insert. Most of these tetrads exhibited gene conversion of a d(TG.AC)n insert. However, the insertion of d(TG.AC)n sequences had no effect on the frequency of gene conversion of closely linked marker genes. Surprisingly, when d(TG.AC)n sequences were present on only one homolog at the HIS3 locus, one-half of the tetrads exhibiting nonparental segregation for marker genes that flanked the repetitive DNA insert were very unusual and appeared to have arisen by multiple recombination events in the vicinity of the d(TG.AC)n insert. Similar multiply recombinant tetrads were seen in crosses in which d(TG.AC)n sequences were present on both homologs. Combined, the data strongly suggest that d(TG.AC)n sequences significantly enhance reciprocal meiotic recombination and may be important in causing multiple recombination events to occur within a relatively small region of the yeast chromosome. Molecular evidence is presented that clearly documents the postmeiotic segregation of an 80-base stretch of d(TG.AC)n.

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