Discrimination of Repetitive Sequences Polymorphism in Secale cereale by Genomic In Situ Hybridization-Banding

Genomic in situ hybridization banding （GISH-banding）, a technique slightly modified from conventional GISH, was used to probe the Chinese native rye （Secale cereale L.） DNA, and enabled us to visualize the individual rye chromosomes and create a universal reference karyotype of the S. cereale chromosome 1R to 7R. The GISH-banding approach used in the present study was able to discriminate S. cereale chromosomes or segments in the wheat （Triticum aestivum L.） background, including the Triticale, wheat-rye addition and translocation lines. Moreover, the GISH-banding pattern of S. cereale subsp. Afghanicum chromosomes was consistent with that of Chinese native rye cv. Jingzhou rye; whereas the GISH-banding pattern of Secale vavilovii was different from that of S. cereale, indicating that GISH-banding can be used to study evolutionary polymorphism in species or subspecies of Secale. In addition, the production and application of GISH-banding to the study of adenine-thymine-riched heterochromaUn is discussed.

Repetitive DNA Sequences from the X Chromosome of the Spiny Eel (Mastacembelus aculeatus)

To investigate the characters of repetitive DNA sequence in the sex chromosomes of the spiny eel （Mastacembelus aculeatus）, the X chromosomal library was screened and a family of repetitive sequence, consisting of Ma 1-Ma 6, was isolated. The fluorescence in situ hybridization （FISH） result confirmed that Ma 1- Ma 5 dispersed over sex chromosomes and all autosomes, whereas, Ma 6 is sex chromosome-specific and distributed only on the C-band positive regions of X chromosome, and Ma 6 maybe the main components of the heterochromatic regions of X chromosome. This study provides additional information about the evolution of sex chromosomes in lower vertebrates such as fish.

Integrating the physical and genetic map of bread wheat facilitates the detection of chromosomal rearrangements

The bread wheat genome harbors a high content of repetitive DNA,which is amenable to detection and characterization using fluorescence in situ hybridization(FISH)karyotyping.An integrated genetic map was derived from a recombinant inbred population bred from a cross between a synthetic hexaploid wheat and a commercial Chinese bread wheat cultivar,based on 28 variable FISH sites and>150000 single nucleotide polymorphism(SNP)loci.The majority(20/28)of the variable FISH sites were physically located within a chromosomal region consistent with the genetic location inferred from that of their co-segregating SNP loci.The eight exceptions reflected the presence of either a translocation(1 R/1 B,1 A/7 A)or a presumptive intra-chromosomal inversion(4 A).For eight out of the nine FISH sites detected on the Chinese Spring(CS)karyotype,there was a good match with the reference genome sequence,indicating that the most recent assembly has dealt well with the problem of placing tandem repeats.The integrated genetic map produced for wheat is informative as to the location of blocks of tandemly repeated DNA and can aid in improving the quality of the genome sequence assembly in regions surrounding these blocks.

Gene deletion and carrier detection in the family of Becker muscular dystrophy by short tandem repeat sequence polymorphism

Objective To type haplotypes among the patients, carriers and normal offspring in a family of males with Becker muscular dystrophy in one generation by allelic fragment length polymorphism analysis. Methods Deletion analysis of the patients were performed using multiplex polymerase chain reaction (PCR) of amplification with 9 dystrophin exon primers. Intragenic short tandem repeat (STR) sequence (STR44, STR45, STR49 and STR50) were amplified by PCR to analyse allelic fragment length polymorphisms in the members of the family. Results The deletions of exons 17, 19 and 45, as well as deletions of allelic fragments at the loci of STR44 and STR45 were determined in the patients. Hemizygosity at those two loci were detected and carrier status ascertained in the mother of the patients. The normal haplotypes were typed in the sister of the patients. Conclusion The method of STR sequence polymorphism analysis can determine haplotypes at normal status or at risk status. It would be used in prenatal diagnosis and carrier detection in the families of Duchenne and Becker muscular dystrophy.

Heterozygosity of Knob-Associated Tandem Repeats and Knob Instability in Mitotic Chromosomes of Zea （Zea mays L. and Z. diploperennis Iltis Doebley）

Knobs are blocks of heterochromatin present on chromosomes of maize （Zea mays L.） and its relatives that have effects on the frequency of genetic recombination, as well as on chromosome behavior. Knob heterozygosity and instability in six maize inbred lines and one Z. diploperennis Iltis Doebley line were investigated using the fluorescence in situ hybridization （FISH） technique with knob-associated tandem repeats （180 bp and 350 bp （TR- 1）） as probes. Signals of seven heterozygous knobs containing 180- bp repeats and of one heterozygous knob containing TR- 1 were captured in chromosomes of all materials tested according to the results of FISH, which demonstrates that the 180-bp repeat is the main contributor to knob heterozygosity compared with the TR- 1 element. In addition, one target cell with two TR- 1 signals on one homolog of chromosome 2L, which was different from the normal cells in the maize inbred line GB57, was observed, suggesting knob duplication and an instability phenomenon in the maize genome.