Genetic and molecular markers of the Queensland fruit fly, Bactrocera tryoni.

Twenty-six microsatellite markers, along with two restriction fragment length polymorphism (RFLP) markers and three morphological markers, have been mapped to five linkage groups, corresponding to the five autosomes of the Queensland fruit fly, Bactrocera tryoni. All these molecular and genetic markers were genotyped in three-generation pedigrees. Eight molecular markers were also localized to the salivary gland polytene chromosomes by in situ hybridization. This provides a substantial starting point for an integrated genetic and physical map of B. tryoni.

Synaptonemal complex analysis of domestic sheep (Ovis aries) with Robertsonian translocations. III. Deficient pairing and NOR role in Massey III heterozygotes.

Spermatocytes from rams heterozygous for Massey translocation III (t(3)7;25) contained one trivalent and those from the rams heterozygous for both Massey translocations I and III (t1t3) contained two trivalents. Where two trivalents and the XY pair are present in the same nucleus they may form a synaptonemal complex (SC), but no SC segment is found between the two trivalents. The frequency of pairing abnormality in four t3 rams and two t1t3 rams did not significantly differ from that in the normal sheep, but t3 trivalents with diverse abnormal configurations were recorded. A hypothesis was proposed that nucleolar organizer regions (NORs) or nucleoli could account for deficient pairing behaviour and hence chromosome rearrangement, because the NOR region on an NOR-bearing chromosome was usually delayed in pairing, and unpaired regions tended to associate with other unpaired axes or SCs.

Synaptonemal complex analysis of domestic sheep (Ovis aries) with Robertsonian translocations. I. Pachytene karyotype substaging of normal sheep.

Meiotic chromosome pairing behaviour in three normal sheep was surveyed by synaptonemal complex (SC) analysis at the electron microscope level. The SC karyotype of normal rams is composed of a sex pair, three metacentric or submetacentric pairs, and 23 acrocentric autosomal bivalents, with the total autosomal SC length ranging from 309 to 315 mircrons. Five nucleoli are terminally located on the three metacentric, and one large and one small acrocentric autosomal bivalents. XY morphology was used to divide pachytene into five substages. Although pairing abnormalities (mostly SC interactions) were recorded in an average of 16% of the spermatocytes, bivalent-XY association occurred in only 4.7% of the cells.

Synaptonemal complex analysis of domestic sheep (Ovis aries) with Robertsonian translocations. II. Trivalent and pairing abnormalities in Massey I and Massey II heterozygotes.

Zygotene and pachytene spermatocytes from Massey I (t1 5;26) and Massey II (t2 8; 11) translocation heterozygotes each contained one trivalent, often delayed in pairing, while cells from double Massey translocation heterozygotes had two such trivalents. As meiosis progressed, trivalents became fully paired, with acrocentric axes in a cis configuration. Abnormal pairing configurations often resulted from interactions between unpaired chromosome axes or segments. However, when two Massey trivalents were present in the same nucleus, there was no pairing interaction between them. In different Massey translocation heterozygotes, trivalent-involved pairing abnormalities occurred in 14-28% of cells, with XY-trivalent and XY-bivalent-trivalent associations being as high as 7.1-23.1%. In spermatocytes from single and double Massey translocation heterozygotes with normal-sized testes, the total SC abnormality frequency was 34.4% for the t1 heterozygotes, 27.1% for the t2 heterozygotes, and 21.4% for the double heterozygote. One Massey II heterozygote with one normal and one small testis had significantly higher SC abnormality frequency (54%) than normal rams. A trisomic cell was recorded in one ram and two hyperdiploid cells in another ram, but these were unrelated to the translocations. It is suggested that resolution of pairing abnormalities by synaptic adjustment is important in reducing the effects on fertility of the translocations.

Synaptonemal complex analysis of hybrid and purebred water buffaloes (Bubalus bubalis).

The morphology of the synaptonemal complex (SC) in river (2n = 50) and swamp (2n = 48) water buffaloes and their hybrids, was studied by electron microscopic analysis. In 2n = 49 hybrids, F2 and backcrosses the formation and pairing behaviour of a trivalent at zygotene-pachytene confirmed that river and swamp buffaloes differ by a centromere-to-telomere (C-T) tandem fusion. While 29% of spermatocytes from a purebred river buffalo and 16% from a purebred swamp buffalo had pairing abnormalities, a significantly higher frequency of abnormalities (48-72%) was recorded in F1, F2, and backcrosses with 2n = 48, 49 or 50. Highest abnormality frequencies occurred in 2n = 49 bulls. Abnormal pairing configurations often resulted from interactions between unpaired chromosome axes or segments. Zygotene-pachytene meiotic progress appeared delayed in hybrid bulls, and the frequency of SC abnormalities decreased from XY type I substage to type V substage. The variation in SC abnormality data from hybrids was consistent with the levels of sperm abnormality previously reported.

Synaptonemal complex analysis of hybrid cattle. II. Bos indicus x Bos taurus F1 and backcross hybrids.

The levels of meiotic chromosome pairing abnormalities observed in six Australian F1 Bos indicus x Bos taurus cattle crosses (mean = 23%) were significantly higher than those of the full-blood breeds (9%). The abnormal configurations in the F1 hybrids included partial pairing failure, multivalents, interlocks, and inversion pairing. Abnormal configurations were also present, but at lower frequency, in backcross hybrid bulls. The main types of abnormal configurations and the levels of XY-autosomal associations and autosomal asynapsis observed were unlikely to cause significant fertility problems in the hybrids.

Synaptonemal complex analysis of hybrid cattle. III. Meiotic pairing mechanisms in F1 Brahman x Hereford hybrids.

The mechanisms of homologous chromosome pairing were studied in synaptonemal complex (SC) spreads of F1 Brahman (Bos indicus) x Hereford (Bos taurus) cattle. The most common SC abnormalities were bivalents with partial pairing failure and interlocks. While C-band polymorphisms could underlie most of the SC abnormalities observed in the full-blood cattle, other causes seem also to be contributing in the hybrids. The pattern of the abnormalities indicates that genic differences between the species were probably involved. Pachytene substaging data suggest that in some spreads, early pachytene bivalents with partial pairing failure may achieve complete synapsis or may be converted to interlocks by late pachytene.

Synaptonemal complex analysis of hybrid cattle. I. Pachytene substaging and the normal full bloods.

Meiotic chromosome pairing abnormalities in full-blood and hybrid Bos taurus and B. indicus cattle have been surveyed by electron microscopy of pachytene synaptonemal complex spreads. In this paper the full-blood spreads are described in detail, including the use of XY and nucleolar morphology and other measured parameters for pachytene substaging. Pairing abnormalities were observed in up to 9% of the full-blood spreads. Most of these pairing abnormalities (83%) occurred in early-pachytene spreads, suggesting that the mechanism of synaptic adjustment may operate in cattle.

The effect of Ph gene alleles on synaptonemal complex formation in Triticum aestivum × T. kotschyi hybrids.

Chromosome pairing at zygotene-pachytene was studied in Triticum aestivum × T. kotschyi hybrids (2n=5x=35, genomic constitution ABDC(U)S(v)) by electron microscopy of synaptonemal complexes in spread microsporocyte nuclei. Hybrids carrying either the Ph allele or the ph allele, which differ markedly in metaphase I pairing, are both capable of greater than 90% pachytene pairing, although pairing in the Ph hybrids appeared slower or less synchronised. In both genotypes branched synaptonemal complexes were formed by intra-and interchromosomal pairing. The Ph gene control on homoeologous pairing does not act on the ability to pair into synaptonemal complexes. It may act on the rate of pairing or the time of crossing over.

Fertile male tortoiseshell cats. Mosaicism due to gene instability?

Two fertile male tortoiseshell Burmese cats with atypical coat color distribution were found to have normal 38XY karyotypes. Synaptonemal complex analysis of one of these cats revealed normal meiotic pairing. Progeny data indicated that both cats were transmitting both alleles at the sex-linked orange locus, but with unequal frequencies. For one of these cats, analysis of pedigree and progeny data indicated that gene instability at the orange locus was the only possible explanation for its mosaicism. A third male tortoiseshell Burmese cat with typical tortoiseshell phenotype was found to be 39XXY and sterile.

The Relationship between Synaptinemal Complexes, Recombination Nodules and Crossing over in NEUROSPORA CRASSA Bivalents and Translocation Quadrivalents.

Reconstruction of serially sectioned zygotene and pachytene nuclei has allowed the estimation of both the number and position of central component recombination nodules in the synaptinemal complexes of two chromosomally different strains of Neurospora crassa. In both strains the number of nodules is that expected if each nodule represents one crossover event (50 map units). The distribution of nodules within the arms of bivalents shows evidence of centromeric repulsion and telomeric localization. Nodules appear quite early in the zygotene before pairing of chromosomes is complete. Evidence was found of size differences in nodules, and multiple nodules were occasionally seen. Chromosome lengths and nuclear sizes increased from early zygotene to late pachytene. The three quadrivalents present in the alcoy translocation heterozygotes were readily distinguishable in reconstructions, and their cytological dimensions were in agreement with predictions from linkage map distances.