CHROMOSOME EVOLUTION: REPETITIVE EUCHROMATIC CHROMOSOMAL SEGMENTS IN HAWAIIAN DROSOPHILA

1973 ◽  
Vol 15 (1) ◽  
pp. 171-175 ◽  
Author(s):  
Jong Sik Yoon ◽  
Marshall R. Wheeler
Keyword(s):  
Chromosome Evolution ◽  
Gene Action ◽  
Chromosomal Rearrangements ◽  
Rapid Evolution ◽  
Drosophila Species ◽  
Crossing Over ◽  
Hawaiian Drosophila ◽  
Unequal Crossing Over

We have found five distinct chromosomal regions which are repeated within the genomes of 11 endemic Hawaiian Drosophila species. One of the duplications was observed in more than 130 species (of three genera) of Hawaiian Drosophilidae. These "repeats" show synapsis in some nuclei, not in others; repeated segments are sometimes tandem while others are separated on their respective chromosomes. From these observations, one can speculate that chromosomal rearrangements produced by unequal crossing over due to such "repeats," and the possible development of new or modified gene action may provide, at least in part, an explanation of the remarkably rapid evolution and speciation in Hawaiian Drosophila.

Metaphase karyotype identity in four homosequential Drosophila species from Hawaii

1985 ◽  
Vol 27 (3) ◽  
pp. 308-311 ◽  
Author(s):  
Linda S. Chang ◽  
Hampton L. Carson
Keyword(s):  
Polytene Chromosome ◽  
Chromosomal Rearrangements ◽  
The Other ◽  
Drosophila Species ◽  
Mitotic Metaphase ◽  
Metaphase Chromosomes ◽  
Hawaiian Drosophila ◽  
Gross Chromosomal Rearrangements ◽  
Rule Out

Four recently evolved species of Hawaiian Drosophila (silvestris, heteroneura, dijferens, and planitibia) have previously been shown to be homosequential in all five polytene chromosome arms. This suggests that the changes involved in speciation are at the genic level and hence are not evident in the polytene banding sequences. Because this does not rule out the occurrence of heterochromatic differences between these homosequential species, the present study was carried out to examine this possibility. These species are now shown to have identical heterochromatin distributions in mitotic metaphase chromosomes. This proves that neither gross chromosomal rearrangements nor novel heterochromatic blocks have been involved in the divergence of these four species. A fifth, and evolutionarily more distant, species (hemipeza) belonging to the same subgroup has a significantly different heterochromatin distribution from the other four species.Key words: heterochromatin, metaphase karyotypes, Hawaiian Drosophila.

scholarly journals A Game of Thrones at Human Centromeres I. Multifarious structure necessitates a new molecular/evolutionary model

2019 ◽  
Author(s):  
William R. Rice
Keyword(s):  
Spatial Organization ◽  
Repeat Unit ◽  
Rapid Evolution ◽  
Evolutionary Model ◽  
Generic Model ◽  
Crossing Over ◽  
Unequal Crossing Over ◽  
Centromeric Repeat ◽  
Repeat Units ◽  
Protein Binding Sequence

Human centromeres form over arrays of tandemly repeated DNA that are exceptionally complex (repeats of repeats) and long (spanning up to 8 Mbp). They also have an exceptionally rapid rate of evolution. The generally accepted model for the expansion/contraction, homogenization and evolution of human centromeric repeat arrays is a generic model for the evolution of satellite DNA that is based on unequal crossing over between sister chromatids. This selectively neutral model predicts that the sequences of centromeric repeat units will be effectively random and lack functional constraint. Here I used shotgun PacBio SMRT reads from a homozygous human fetal genome (female) to determine and compare the consensus sequences (and levels of intra-array variation) for the active centromeric repeats of all the chromosomes. To include the Y chromosome using the same technology, I used the same type of reads from a diploid male. I found many different forms and levels of conserved structure that are not predicted by –and sometimes contradictory to– the unequal crossing over model. Much of this structure is based on spatial organization of three types of ~170 bp monomeric repeat units that are predicted to influence centromere strength (i.e., the level of outer kinetochore proteins): one with a protein-binding sequence at its 5’ end (a 17 bp b-box that binds CENP-B), a second that is identical to the first except that the b-box is mutated so that it no longer binds CENP-B, and a third lacking a b-box but containing a 19 bp conserved “n-box” sequence near its 5’ end. The frequency and organization of these monomer types change markedly as the number of monomers per repeat unit increases, and also differs between inactive and active arrays. Active arrays are also much longer than flanking, inactive arrays, and far longer than required for cellular functioning. The diverse forms of structure motivate a new hypothesis for the lifecycle of human centromeric sequences. These multifarious levels of structures, and other lines of evidence, collectively indicate that a new model is needed to explain the form, function, expansion/contraction, homogenization and rapid evolution of centromeric sequences.

Mapping Unequal Crossing over Hotspot Region of Simple Sequence Repeat in Maize

2009 ◽  
Vol 35 (5) ◽  
pp. 958-961
Author(s):  
Ji-Hua TANG ◽  
Xi-Qing MA ◽  
Wen-Tao TENG ◽  
Jian-Bing YAN ◽  
Jing-Rui DAI ◽  
...  
Keyword(s):  
Simple Sequence Repeat ◽  
Crossing Over ◽  
Sequence Repeat ◽  
Unequal Crossing Over ◽  
Simple Sequence

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

scholarly journals The M26 Hotspot of Schizosaccharomyces pombe Stimulates Meiotic Ectopic Recombination and Chromosomal Rearrangements

Genetics ◽  
1998 ◽  
Vol 149 (3) ◽  
pp. 1191-1204 ◽  
Author(s):  
Jeffrey B Virgin ◽  
Jeffrey P Bailey
Keyword(s):  
Homologous Recombination ◽  
Schizosaccharomyces Pombe ◽  
Dna Sequences ◽  
Chromosomal Rearrangements ◽  
Low Frequency ◽  
Repeated Sequences ◽  
Crossing Over ◽  
Ectopic Recombination ◽  
Recombination Hotspots ◽  
Integration Sites

Abstract Homologous recombination is increased during meiosis between DNA sequences at the same chromosomal position (allelic recombination) and at different chromosomal positions (ectopic recombination). Recombination hotspots are important elements in controlling meiotic allelic recombination. We have used artificially dispersed copies of the ade6 gene in Schizosaccharomyces pombe to study hotspot activity in meiotic ectopic recombination. Ectopic recombination was reduced 10–1000-fold relative to allelic recombination, and was similar to the low frequency of ectopic recombination between naturally repeated sequences in S. pombe. The M26 hotspot was active in ectopic recombination in some, but not all, integration sites, with the same pattern of activity and inactivity in ectopic and allelic recombination. Crossing over in ectopic recombination, resulting in chromosomal rearrangements, was associated with 35–60% of recombination events and was stimulated 12-fold by M26. These results suggest overlap in the mechanisms of ectopic and allelic recombination and indicate that hotspots can stimulate chromosomal rearrangements.

Unequal Crossing-over in Unique PABP2 Mutations in Japanese Patients

2002 ◽  
Vol 59 (3) ◽  
pp. 474 ◽  
Author(s):  
Mika Nakamoto ◽  
Satoshi Nakano ◽  
Shingo Kawashima ◽  
Masafumi Ihara ◽  
Yo Nishimura ◽  
...  
Keyword(s):  
Japanese Patients ◽  
Crossing Over ◽  
Unequal Crossing Over

scholarly journals Possible role of natural selection in the formation of tandem-repetitive noncoding DNA.

Genetics ◽  
1994 ◽  
Vol 136 (1) ◽  
pp. 333-341
Author(s):  
W Stephan ◽  
S Cho
Keyword(s):  
Natural Selection ◽  
Satellite Dna ◽  
Repeat Length ◽  
Crossing Over ◽  
Recombination Rates ◽  
Noncoding Dna ◽  
Satellite Dnas ◽  
Unequal Crossing Over ◽  
Wide Range ◽  
Long Range Ordering

Abstract A simulation model of sequence-dependent amplification, unequal crossing over and mutation is analyzed. This model predicts the spontaneous formation of tandem-repetitive patterns of noncoding DNA from arbitrary sequences for a wide range of parameter values. Natural selection is found to play an essential role in this self-organizing process. Natural selection which is modeled as a mechanism for controlling the length of a nucleotide string but not the sequence itself favors the formation of tandem-repetitive structures. Two measures of sequence heterogeneity, inter-repeat variability and repeat length, are analyzed in detail. For fixed mutation rate, both inter-repeat variability and repeat length are found to increase with decreasing rates of (unequal) crossing over. The results are compared with data on micro-, mini- and satellite DNAs. The properties of minisatellites and satellite DNAs resemble the simulated structures very closely. This suggests that unequal crossing over is a dominant long-range ordering force which keeps these arrays homogeneous even in regions of very low recombination rates, such as at satellite DNA loci. Our analysis also indicates that in regions of low rates of (unequal) crossing over, inter-repeat variability is maintained at a low level at the expense of much larger repeat units (multimeric repeats), which are characteristic of satellite DNA. In contrast, the microsatellite data do not fit the proposed model well, suggesting that unequal crossing over does not act on these very short tandem arrays.

Quantitative Analysis of C-bands in Chromosomes 1, 9, 16, and Y of Twins

1983 ◽  
Vol 32 (3-4) ◽  
pp. 257-260 ◽  
Author(s):  
Marise P. Pedrosa ◽  
F.M. Salzano ◽  
Margarete S. Mattevi ◽  
Judith Viégas
Keyword(s):  
Quantitative Analysis ◽  
Crossing Over ◽  
Same Sex ◽  
Genetic Determination ◽  
Unequal Crossing Over

Thirty-two pairs of Caucasoid twins, 16 monozygotic (MZ) and 16 dizygotic (DZ) of the same sex, were studied by densitometry in relation to the C-bands of chromosomes 1, 9, 16, and Y. Confirming earlier results, concordance was not absolute among MZ. Estimates of the degree of genetic determination for these traits varied from 0.73 to 0.89 for the autosomes and from 0.86 to 0.95 for the Y. There are now stronger indications that a fraction of the intergeneration variability found in these structures may be real, probably due to mitotic and/or meiotic unequal crossing-over.

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