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PubMed1981

Pericentric inversions of chromosome 12 in two families.

Two cases of pericentric inversion of chromosome 12 are presented, one 46,XX,inv(12)(p13;q11) and the other was also a heterozygotic carrier of the inversion. These inversions were detected among 4035 cytogenetic analyses carried out in patients with psychosomatic retardation and/or malformations (357 with a Down phenotype) and in patients with histories of miscarriages, sterility, or growth failure. In cases studied from a review of the literature together with our own we found that among 3235 cases of Down syndrome there were 7 patients with trisomy 21 and inherited balanced reciprocal translocation involving chromosomes other than pair 21. The frequent participation of some chromosomes in these balanced reciprocal translocations, above all those of group A (1-3), suggests that these and probably other rearrangements could make the segregation of chromosome 21 easier.

Child↗
PubMed1983

Duplication of the segment q12.2 leads to qter of chromosome 22 due to paternal inversion 22(p13q12.2).

A 1730-g male infant, born at 37 weeks gestation, had multiple congenital anomalies, consisting of microcephaly, hypertelorism, bilateral cleft lip and palate, micrognathia, low-set ears, and cryptorchidism. Chromosome analysis showed a recombinant 22 derived from the paternal inversion (22)(p13q12.2). The proband's karyotype is 46,XY,rec(22),dup q,inv(22)(p13q12.2)pat, which has a duplication of q12.2 leads to qter. An identical recombinant has been reported in a female infant in Mexico whose mother was a carrier of the inversion. Similar congenital anomalies present in these two patients demonstrate the phenotype of duplication of the distal long arm 22. This report also documents the occurrence of an identical inversion in two apparently unrelated Mexican families.

Abnormalities, Multiple↗
PubMed1980

Cytogenetic study of a large black kindred: inversions, heteromorphisms, and segregation analysis.

Q-and C-band heteromorphisms were determined by sequentially staining cells from 81 members of an American Black kindred. The incidence of heteromorphs is reported for 14 people who married into the family. Small pericentric inversions of chromosome 3 were found in 23 kindred members, three of whom were homozygous. Six 'complete' chromosome 9 inversions and a single 'partial' inv9 were detected. there was no apparent phenotypic effect associated with the inversions, nor were duplication-deficiency chromosomes observed. Evidence for preferential segregation of Q-heteromorphs is reported, and comparison with data from other authors points to chromosome 13 as showing the most distortion.

Black People↗
PubMed1986

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22).

Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 7. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These results suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.

Animals↗
PubMed1978

Inversion of 'flourescent' segment in chromosome 3: a polymorphic trait.

The frequency of the 'inversion' of flourescent constitutive heterochromatin in chromosome 3 was the same in a sample of 370 retarded persons as in a sample of 222 mentally normal men. It can be concluded that this 'inversion' is not associated with mental retardation. This variant is more common (4%) in the Canadian population we studied than in samples reported by most other authors (0-1.7%). Possibly the founder effect could play a role in the differences. Two cases of homozygotes for this 'inversion' were identified.

Adolescent↗
PubMed1986

Loop formation and synaptic adjustment in a human male heterozygous for two pericentric inversions.

Pachytene analysis was undertaken in an infertile male heterozygous for two pericentric inversions of chromosomes 1 and 9. The synaptic behaviour of the bivalent 1 inversion was the most informative. Analysis of the chromomere pattern combined with centromeric heterochromatin staining allowed precise description of synaptic initiation and extension leading to the homosynapsed loop. These techniques also allowed demonstration of the existence of heterosynapsis following alignment of the inverted segments. Non-homologous synapsed bivalents had the morphological aspects of straight bivalents with two distant blocks of centromeric heterochromatin. The numbering of the autosomal bivalent chromomeres at various successive phases of the inversion loop behaviour of bivalent 1 permitted us an alternative approach to the timing of pachytene.

Adult↗
PubMed1982

A near terminal pericentric inversion leads to nitrogen metabolite derepression in Aspergillus nidulans.

The mutation xprD-1, previously shown to be an allele of the areA gene and to lead to nitrogen metabolite derepression in Aspergillus nidulans, is shown to be associated with a near terminal pericentric inversion in linkage group III. The left arm break-point is between the adI and sC genes, and the right arm break-point is between the ornC and areA genes but just centromere proximal to areA. In crosses of xprD-1 strains to inversion-free strains one class of duplication-deficiency progeny is recovered. These progeny have two copies of the distal portion of the left arm beginning just before sC but lack a copy of areA and the region distal to it on the right arm. The viability of these duplication-deficiency progeny indicates that no indispensable gene can lie distal to areA, suggesting proximity of areA to the telomere. The inversion might increase expression of areA which, given the positive acting nature of this regulatory gene, would result in nitrogen metabolite derepression. If increased expression be the result of fusion to (or creation of) a more efficient promoter and/or ribosome binding sequence, areA must be transcribed towards the right arm telomere.

Alleles↗
PubMed1975

Cytological observations on the interaction between two inversions responsible for position-effect variegation in Drosophila melanogaster.

The strain of Drosophila melanogaster In (1)mK; In (2LR) RevB shows more miniature variegation than the strain In(1)mK and less Revolute variegation than the strain In(2LR) RevB. Observations on heterochromatisation in the larval salivary gland chromosomes of the three strains revealed that the mK chromosome is heterochromatised in a higher proportion of nuclei and the RevB chromosome is heterochromatised in a lower proportion of nuclei in the double-inversion strain than in the corresponding single-inversion strain. Single- and double-inversion strains did not however differ in the mean number of bands heterochromatised per affected chromosome. The difference between incidence and extent of heterochromatisation was further exposed by comparisons between and within strains: the incidence of heterochromatisation in different chromosome regions within a nucleus was positively correlated, but a significant positive correlation was found in only one of the eight possible comparisons between extents of heterochromatisation in different chromosome regions in a given nucleus, two of the comparisons showing significantly negative correlations. The results in general are compatible with the view that the initiation and progression of heterochromatisation are distinct phenomena, under separate control.

Animals↗
PubMed1988

A recombinant X chromosome in a short statured girl resulting from a maternal pericentric inversion.

A 7 3/4-year-old girl with short stature was found to have a recombinant (X),dup q chromosome resulting from an apparently unique pericentric inversion (X)(p11.2q26) present in her mother and maternal grandmother. The recombinant X chromosome was shown to be late replicating and the inversion X chromosome to be randomly inactivated. This appears to be only the eighth report (7 female, 1 male) of a recombinant resulting from an X pericentric inversion despite all diagnosed females having mild clinical abnormalities. Reasons for the rarity of such recombinant X chromosomes in man are examined.

Child↗
PubMed1989

Molecular cloning of alpha-amylase genes from Drosophila melanogaster. III. An inversion at the Amy locus in an amylase-null strain.

Overlapping clones of the structural gene region for alpha-amylase, Amy, were isolated from a lambda EMBL4 library containing genomic DNA fragments from an amylase-null strain of Drosophila melanogaster. Southern blot analysis and restriction endonuclease mapping of the cloned region indicate that it contains an Amy gene duplication within an inverted repeat sequence as is characteristic of the genomic arrangement for this species. Spacing between the cloned gene copies is similar to that commonly found in other strains. Evidence is presented for the presence of an inversion 4 to 9 kb in length within the cloned Amy region of the null strain. We postulate a causal relationship between the presence of the inversion and the failure of individuals from the null strain to express amylase. A model is proposed that suggests the inversion may have arisen through intramolecular (or sister-strand) recombination mediated by homologous pairing of the inverted repeat sequences at the Amy locus.

Animals↗
PubMed1987

Homozygous paracentric inversion 12 in a mentally retarded boy: a case report and review of the literature.

A mentally retarded male was found to be homozygous for a paracentric inversion of the long arm of chromosome 12(inv(12)(q21.1q23.2]. His parents, who are first cousins, and his phenotypically normal younger brother are inversion heterozygotes. Homozygous structural rearrangements are discussed and cases of paracentric inversions, including a further nine previously unpublished, are reviewed.

Adolescent↗
PubMed1985

The endpoints of an inversion in wheat chloroplast DNA are associated with short repeated sequences containing homology to att-lambda.

The endpoints of an inversion in wheat chloroplast DNA are shown to be associated with copies of a short repeated sequence. Recombination across the repeats in an inverted configuration may have been responsible for the inversion, although they are currently in a direct orientation owing to a second inversion. The repeated sequence contains an element homologous to the core of the bacteriophage lambda att-site, which can function as such in vivo.

Bacteriophage lambda↗
PubMed1986

Effect of gamma rays at the dihydrofolate reductase locus: deletions and inversions.

A series 11 gamma-ray-induced mutants at the dihydrofolate reductase (dhfr) locus in Chinese hamster ovary cells has been examined for the types of DNA sequence change brought about by this form of ionizing radiation. All 11 mutants were found to have suffered major structural changes affecting the dhfr gene. In eight of the mutants, all or part of the dhfr gene has been deleted. The extent of these deletions was examined in seven of these mutants and, for comparison, in two deletion mutants that were induced by UV irradiation. For this purpose, probes from an overlapping set of cosmids that span 210 kb of DNA in this region were used. Three of seven gamma-ray-induced mutants and one UV-induced mutant were shown to have deleted the entire 210-kb region. In the remaining mutants, endpoints ranging from within the dhfr gene to 100 kb downstream were observed. No upstream endpoints were detected, so that an upper limit on the size of these large deletions could not be assigned. Three of the 11 gamma-ray-induced mutants contained an interruption in the dhfr gene without any detectable loss of sequence. Restriction analysis of these interrupted mutants showed that at least 8-14 kb of "foreign" DNA sequence became joined to the gene at the point of disruption. Cytogenetic analysis of these mutants showed that in two cases an inversion of the banding pattern on chromosome Z-2 had taken place. The inverted dhfr mutants contain very low amounts of dhfr RNA sequences, and the 5' end of an inversion mutant gene exhibits the same pattern of DNA methylation and DNase I-hypersensitivity as the wild-type gene. Our results suggest that ionizing radiation causes primarily, if not exclusively, large deletions and inversions in mammalian cells.

Animals↗
PubMed1990

Synapsis in single and double heterozygotes for partially overlapping inversions in chromosome 1 of the house mouse.

Electron microscopic (EM) analysis of synaptonemal complexes (SC) in single and double heterozygotes for the partially overlapping inversions In(1)1Icg, In(1)1Rk and In(1)12Rk in chromosome 1 of the house mouse reveals that synapsis and synaptic adjustment are dependent on the size and location of the inversions and interaction between the latter. Is(1)1Icg contains insertions of the inverted repeats Is(HSR;1C5)1Icg and Is(HSR;1D)2Icg and an inverted euchromatic region. Synaptic adjustment of the D-loops by shortening of the asynapsed segments of the lateral elements belonging to the insertions occurs at the late zytogene to early pachytene stage. Synaptic adjustment of the inversion loops takes place at early to late pachytene. A delay in adjustment was found in the double heterozygotes In(1)1Icg/In(1)1Rk and In(1)1Icg/In(1)12Rk. A correspondence between the lifespan of asynapsis in inverted regions and the probability of association of XY and heteromorphic bivalents was revealed.

Animals↗
PubMed1995

Familial pericentric inversion incidentally detected at prenatal diagnosis.

A case of familial heterozygous pericentric inversion of chromosome 1 [inv(1)(p13q23)] is presented. The inversion was incidentally detected in a fetus whose mother received prenatal chromosomal diagnosis due to her age (40 years old), and thereafter the same inversion was detected in the father whose phenotype was normal. No abnormalities were found in the phenotype of the newborn carrier. Semen analysis of the father revealed normal findings. The couple had no history of spontaneous abortion.

Adult↗
PubMed1995

Analysis of Tn5 inversion events in Escherichia coli plasmids.

The ability of the bacterial transposon Tn5 to undergo sequence inversion in Rec+ Escherichia coli cells as a result of recombination between its duplicated IS50 elements was examined using specially designed plasmid constructs. Surprisingly, recombination events in the IS50 elements that led to crossover and therefore Tn5 inversion could be detected at a frequency of only 10(-5). This was approximately an order of magnitude lower than the frequency of IS50 recombination that led to conversion events (i.e. non-reciprocal recombination) without crossover, and at least two orders of magnitude lower than the frequency of intermolecular recombination between IS50 elements on two different plasmids. These rare conversion and inversion events in Tn5 appeared to be due to intramolecular recombination and not simply to multiple rounds of reciprocal crossing over, since the heterodimeric intermediates that would be generated during the latter process could be readily isolated but were shown to yield a completely different set of plasmid products upon resolution.

Chromosome Inversion↗
PubMed1996

Hairpins create minute inversions in non-coding regions of chloroplast DNA.

Minute inversions (4 bp in length), associated with probable hairpin secondary structures, were inferred from comparative analysis of rpl16 intron sequences from the chloroplast genomes of Chusquea species and related bamboos (Poaceae). The inverted sequences, which appear to have arisen independently on several occasions, comprise entire loops of the putative hairpins. The process of inversion seems dependent upon the stem length of the hairpin and its estimated free energy of formation. A similar inversion was uncovered for other plants in a previously published data set for a different non-coding region of the chloroplast genome, suggesting that the inversional process may be a common feature of non-coding DNA evolution. Several implications for phylogenetic analysis are noted.

Base Sequence↗
PubMed1997

The highly rearranged chloroplast genome of Trachelium caeruleum (Campanulaceae): multiple inversions, inverted repeat expansion and contraction, transposition, insertions/deletions, and several repeat families.

Comprehensive gene mapping reveals that the chloroplast genome of Trachelium caeruleum is highly rearranged relative to those of other land plants. Evolutionary scenarios that consist of seven to ten inversions, one or two transpositions, both expansion and contraction of the typically size-conserved inverted repeat, a presumed gene loss, deletions within two large open reading frames and several insertions, are sufficient to derive the Trachelium arrangement from the ancestral angiosperm chloroplast DNA arrangement. Two of the rearrangements disrupt transcriptional units that are otherwise conserved among land plants. At least five families of small dispersed repeats exist in the Trachelium chloroplast genome. Most of the repeats are associated with inversion endpoints and may have facilitated inversions through recombination across homologous repeats.

Biological Evolution↗