Recent linkage-based studies in humans suggest the presence of loci that affect either genome-wide recombination rates, utilization of recombination hotspots, or both. We have been interested in utilizing cytological methodology to directly assess recombination in mammalian meiocytes and to identify recombination-associated loci. In the present report we summarize studies in which we combined a cytological assay of recombination in mouse pachytene spermatocytes with QTL analyses to identify loci that contribute to genome-wide levels of recombination in male meiosis. Specifically, we analyzed MLH1 foci, a marker of crossovers, in 194 F2 male mice derived from a subspecific cross between CAST/EiJ and C57BL/6J parental strains. We then used these data to uncover loci associated with individual variation in mean MLH1 values. We identified seven recombination-associated loci across the genome (on chromosomes 2, 3, 4, 14, 15, 17, and X), indicating that there are multiple recombination “setting” loci in mammalian male meiosis.

In a territory-wide surveillance study, Laribacter hongkongensis was isolated solely from freshwater fish (60% of grass carps, 53% of bighead carps, and 25% of mud carps). Comparing the pulsed-field gel electrophoresis patterns of fish and patient isolates revealed that most patient isolates were clustered together, suggesting that some clones could be more virulent.Laribacter hongkongensis was first discovered in Hong Kong from the blood and empyema pus of a 54-year-old Chinese man with alcoholic cirrhosis (5). Subsequently, L. hongkongensis was discovered in three of our patients and three patients in Switzerland with community-acquired gastroenteritis (3). In a multicenter prospective study, we confirmed that L. hongkongensis is associated with community-acquired gastroenteritis and traveler's diarrhea (4). Freshwater fish were shown to be a reservoir of L. hongkongensis (4). The isolation of L. hongkongensis from patients who resided in or have recently traveled to Asia, Europe, America, and Africa implied that the bacterium is likely to be of global importance.In this study, in order to determine the prevalence of L. hongkongensis in different animals commonly used for cooking in our locality, we carried out an ecoepidemiology study in Hong Kong. Furthermore, to determine the genetic diversity of L. hongkongensis, all L. hongkongensis isolates were typed by pulsed-field gel electrophoresis (PFGE). The PFGE patterns were compared to those of L. hongkongensis strains isolated from patients with gastroenteritis.Fecal swabs were obtained from 350 pigs and 80 cows, and cloacal swabs were obtained from 400 chickens, 50 ducks, and 50 geese from slaughter houses and poultry farms in Hong Kong with assistance from Veterinary Public Health Section of the Food and Environmental Hygiene Department. Three hundred and sixty freshwater fish (mostly farmed) of six different species and 360 marine fish of six different species commonly purchased for cooking in Hong Kong were obtained from 10 retail food markets (six fish per species per market) located in different districts of Hong Kong. Samples were obtained from the midguts and hindguts of the fish by using sterile cotton wool swabs. All samples were plated onto cefoperazone MacConkey agar and incubated under aerobic conditions at 37°C for 48 h (1). All suspected isolates were identified phenotypically by standard conventional biochemical methods (2). Isolates suspected to be L. hongkongensis were subjected to 16S rRNA gene sequencing (3, 4). All L. hongkongensis isolates were subjected to PFGE (3, 4). Digital images were stored electronically as TIFF files and analyzed visually and with GelCompar II (version 3.0; Applied Maths, Kortrijk, Belgium) by using the Dice coefficient and represented by the unweighted pair-group method using average linkages with 1% tolerance and 0.5% optimization settings.L. hongkongensis was isolated from the midguts and hindguts of 86 (24%) of 360 freshwater fish, including 36 (60%) grass carps, 32 (53%) bighead carps, 15 (25%) mud carps, and...

Trisomy 22 is one of the most common trisomies in clinically recognized pregnancies, yet relatively little is known about the origin of nondisjunction for chromosome 22. Accordingly, we initiated studies to investigate the origin of the extra chromosome in 130 trisomy 22 cases. Our results indicate that the majority of trisomy 22 errors (>96%) arise during oogenesis with most of these errors ( approximately 90%) occurring during the first meiotic division. As with other trisomies, failure to recombine contributed to nondisjunction of chromosome 22. Taken together with data available for other trisomies, our results suggest patterns of nondisjunction that are shared among the acrocentric, but not all nonacrocentric, chromosomes.

Trisomy 13 is one of the most common trisomies in clinically recognized pregnancies and one of the few trisomies identified in liveborns, yet relatively little is known about the errors that lead to trisomy 13. Accordingly, we initiated studies to investigate the origin of the extra chromosome in 78 cases of trisomy 13. Our results indicate that the majority of cases (>91%) are maternal in origin and, similar to other autosomal trisomies, the extra chromosome is typically due to errors in meiosis I. Surprisingly, however, a large number of errors also occur during maternal meiosis II ( approximately 37%), distinguishing trisomy 13 from other acrocentric and most nonacrocentric chromosomes. As with other trisomies, failure to recombine is an important contributor to nondisjunction of chromosome 13.