Biomedical subjects

R G Danzmann

Publications and source records attributed to R G Danzmann.

30 records · Page 2Linked to original sources

PubMed1997

Secondary tetrasomic segregation of MDH-B and preferential pairing of homeologues in rainbow trout.

We examined the inheritance of allelic variation at an isozyme locus, MDH-B, duplicated by ancestral polyploidy in salmonid fishes. We detected only disomic segregation in females. Segregation ratios in males were best explained by a mixture of disomic and tetrasomic inheritance. We propose a two-stage model of pairing in male meiosis in which, first, homologous chromosomes pair and recombine in the proximal region of the chromosome. Next, homeologous chromosomes pair and recombine distally. We suggest that this type of tetrasomic inheritance in which centromeres segregate disomically should be referred to as "secondary tetrasomy" to distinguish it from tetrasomy involving entire chromosomes (i.e., "primary tetrasomy"). Differences in segregation ratios between males indicate differences between individuals in the amount of recombination between homeologous chromosomes. We also consider the implication of these results for estimation of allele frequencies at duplicated loci in salmonid populations.

Alleles↗

PubMed1995

A phylogeographic survey of brook charr (Salvelinus fontinalis) in Algonquin Park, Ontario based upon mitochondrial DNA variation.

Forty-nine populations of brook charr (Salvelinus fontinalis) from Algonquin Park lakes and rivers were analysed for mitochondrial DNA variation. Haplotypic distributions of wild fish in the Algonquin Park region of Ontario, Canada, predominantly reflect postglacial dispersal patterns into the region in spite of substantial hatchery plantings. Two major refugial groupings colonized this regions. Northern and eastern watersheds (Amable du Fond, Bonnechere, and northern Petawawa), were colonized primarily by haplotype 1 fish (B1 phylogenetic assemblage), while Oxtongue River, southern Petawawa, and York River populations were colonized predominately by fish from the B2 and A mtDNA phylogenetic assemblages. Fish with haplotypes in the A and B2 phylogenetic assemblages are common in the Lake Huron drainage. All watersheds in the Park drain into the Ottawa River, except the Oxtongue drainage (part of the Lake Huron watershed). This suggests that early glacial outflows south of the Algonquin Park region (Kirkfield-Trent) may have been colonized by fish that initially invaded 'Ontario island' (south-western Ontario), while fish which invaded northern Algonquin Park were derived from a different refugial grouping(s) which may have involved colonization both up the Ottawa River drainage, and/or from a more westerly (Mississippian) refugial grouping. A majority of the populations in Algonquin Park have been planted with hatchery reared brook charr since the 1940s. The Hills Lake or 'Domestic' strain was used almost exclusively for these plantings. Comparisons of mtDNA haplotypic distributions in hatchery and wild fish suggests that hatchery females had minimal spawning success and/or their progeny had poor survivorship in the wild.

Animals↗

PubMed1988

Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures.

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8 degrees C) and warmer (12 degrees C) than normally experienced by these fish (9.5 degrees C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12 degrees C than at both 5 and 8 degrees C. Fish with different genotypes at Pgm2 and Ck1 showed significant differences in hatching time that were consistent between experiments. Ck1 heterozygotes hatched sooner than homozygotes at 8 degrees C but later at 12 degrees C. Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.

Animals↗

PubMed1988

Temperature-dependent genotypic selection and embryonic survival of rainbow trout.

The survival of rainbow trout (Salmo gairdneri) with different developmental rates and genotypes at eight polymorphic loci was compared in two experiments. The embryos were reared at temperatures colder (5 and 8 degrees C) and warmer (12 degrees C) than normally experienced by the strain (9.5 degrees C). Embryo survival in five different hatching groups (representing the sequential order of hatching) was compared at 8 and 12 degrees C. Embryos in the center of the hatching distribution (groups 2, 3, and 4) showed a greater survival to yolk sac resorption than those in the extremes (groups 1 and 5). These differences are significant in the embryos reared at 12 degrees C in both experiments. Embryo survival from hatching to yolk sac resorption was poorer at 12 compared to 8 degrees C. In the one experiment where it was examined, significantly fewer embryos hatched at 5 and 12 than at 8 degrees C. Significant deviations from genotypic expectations (based upon parental allele frequencies) were detected in the progeny (23 of 34 cases). In contrast, few deviations from Hardy-Weinberg expectations were detected (5 of 34 cases) when progeny allele frequencies are used. Few significant differences in genotype frequencies were detected among the progeny reared at the different temperatures. This suggests that nonequal contributions of parental gametes rather than differential selection of genotypes account for the deviations from expectations in the progeny.

Acclimatization↗

PubMed1988

Developmental rate and viability of rainbow trout with a null allele at a lactate dehydrogenase locus.

We show that a previously described isozyme polymorphism in rainbow trout (Salmo gairdneri) is the result of an enzymatically inactive (i.e., null) allele (n). Ldh3 null homozygotes (n/n) and heterozygotes (100/n) have reductions of about 20 and 12% in total lactate dehydrogenase (LDH) activity at hatching, respectively. As juveniles, (100/n) fish have reductions in LDH activity of 15, 37, and 21% in brain, heart, and white muscle, respectively. Embryos with different Ldh3 phenotypes from 11 families do not differ significantly in either survival or hatching time. However, a second measure of developmental rate, the amount of malate dehydrogenase (MDH) and phosphoglucomutase (PGM) activity in 33-day-old embryos, suggests that (100/n) embryos develop more slowly than (100/100) embryos. In three of four families examined, (100/n) embryos have significantly lower amounts of total MDH activity (8-10%). In one of these, (100/n) embryos also have significantly lower total PGM activity (15%). These data suggest that the reduction in total LDH activity is associated with small but detectable delays in developmental rate but nondetectable differences in survival to hatching.

Aging↗

PubMed1986

Does enzyme heterozygosity influence developmental rate in rainbow trout?

The association between genetic variation at 14 enzyme loci and developmental rate was examined in six strains of rainbow trout (Salmo gairdneri). The purpose of this study was to test the prediction that heterozygotes develop faster than homozygotes. We also tested whether the enzyme loci could be responsible for such an association or are marking chromosomal segments that influence developmental rate. There is a significant negative association (P less than 0.05) between hatching time and the number of heterozygous loci per fish in one of six strains. Heterozygotes developed faster than homozygotes at 26 out of 43 possible comparisons made at individual loci within strains. Heterozygotes developed significantly faster than homozygotes in eight comparisons, and significantly slower in six comparisons. These results suggest a weak positive association between developmental rate and heterozygosity. Nine loci were polymorphic in more than one strain. At five of these loci the hatching distributions of heterozygotes and homozygotes are significantly different among strains. The direction of the relationship between heterozygosity and developmental rate at individual loci is not consistent among strains. Therefore, our results suggest that the loci surveyed are marking chromosomal segments that influence developmental rate. Linkage disequilibrium between alleles at the isozyme loci and dominant-acting genes that accelerate or retard developmental rate is hypothesised to account for the observed relationship between heterozygosity and developmental rate.

Aging↗

PubMed1985

Absence of developmental incompatibility in hybrids between rainbow trout and two subspecies of cutthroat trout.

We examined the developmental rate of hybrids between rainbow trout (Salmo gairdneri) and two subspecies of cutthroat trout: westslope cutthroat trout (Salmo clarki lewisi) and Yellowstone cutthroat trout (Salmo clarki bouvieri). These taxa show considerable genetic divergence at 42 structural loci encoding enzymes; the mean Nei's D between the rainbow trout and the two species of cutthroat trout is 0.22. We used four measures of developmental rate: time of hatching and yolk resorption, rate of increase in activity of four enzymes, and time of initial detection of seven isozyme loci. The two cutthroat trout subspecies reached hatching and yolk resorption earlier than rainbow trout. Cutthroat trout had higher relative enzyme activities than rainbow trout from deposition of eye pigment to hatching. There was no difference in the rate of increase in enzyme activity or time of initial expression of these loci between these species. Hybrids showed developmental rates intermediate or similar to that of the parental species using all measures. Our results indicate an absence of regulatory and developmental incompatibility between these taxa.

Age Factors↗

PubMed1983

Further evidence for a polymorphism in gametic segregation in the tetraploid treefrog Hyla versicolor using a glutamate oxaloacetic transaminase locus.

Intra- and interspecific cross combinations between the tetraploid treefrog Hyla versicolor, and between H. versicolor and the diploid treefrog Hyla chrysoscelis were performed. Progeny phenotypes resulting from these crosses were examined electrophoretically using a polymorphic glutamate oxaloacetic transaminase (GOT-1) locus, to determine the mechanism of chromosome segregation in H. versicolor, and to test theoretical expectations for isozyme expression in interspecific (2n X 4n or 4n X 2n) hybrids. In some intraspecific tetraploid crosses progeny phenotypes fit a disomic mode of segregation, whereas in other crosses a tetrasomic mode of segregation was the most probable. Additional crosses produced phenotypic ratios that conformed to either a disomic or tetrasomic mode of segregation. These results suggest that a polymorphism, with respect to segregation of gametes, exists in H. versicolor, resulting from differences in chromosome pairings during meiosis I. This polymorphism in gametic segregation occurred in both sexes. Certain crosses, however, produced phenotypic ratios that did not conform to any chromosome segregation model. Progeny phenotypes observed from most interspecific crosses conformed to expected interspecific isozyme staining intensity models. Symmetrical heterozygotes, representing either a single dose for both alternate alleles or double doses for both alternate alleles, were also observed. Such phenotypes are unexpected in triploid progeny. A null allele was postulated to account for the aberrant segregation ratios and phenotypes observed in certain intra- and interspecific crosses.

Animals↗

PubMed1982

Isozyme expression in F1 hybrids between carp and goldfish.

Interspecific genetic differences in malate dehydrogenase (MDH), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and esterase (EST) isozymes in carp (Cyprinus carpio) and goldfish (Carassius auratus) were used to examine the allelic expressions in the hybrid between these species. A unique liver SOD and muscle LDH phenotype unambiguously identifies all presumed hybrid individuals. There was no evidence of F2 or backcross phenotypes in hybrid individuals. Liver MDH and EST phenotypes in hybrids show a preferential expression of goldfish isozymes. Variation in the levels of carp liver MDH isozymes may result from the polymorphism of a regulatory mutation effecting isozyme expression, leading to gene silencing after duplication.

Animals↗

PubMed1982

Evidence for a polymorphism in gametic segregation using a malate dehydrogenase locus in the tetraploid treefrog Hyla versicolor.

Artificial cross combinations of tetraploid Hyla versicolor were analyzed electrophoretically using a polymorphic malate dehydrogenase locus (MDH-1) to determine the mechanism of chromosome segregation. Models for differentiating between disomic and tetrasomic inheritance are presented and tested. In some crosses progeny genotypes fit a disomic mode of segregation. In other crosses there is only evidence for a tetrasomic mode of segregation. Additional crosses produced genotypic ratios which conformed to either a disomic or tetrasomic mode of segregation. The same type of inheritance was demonstrated for any individual when used in multiple cross combinations. These results suggest that there exists in H. versicolor a polymorphism with respect to segregation of gametes, resulting from differences in chromosome pairings during meiosis I.

Animals↗

PubMedDate not supplied

Quantitative trait loci for spawning date and body weight in rainbow trout: testing for conserved effects across ancestrally duplicated chromosomes.

We incorporated 69 microsatellite loci into an existing data set of 132 markers to test for quantitative trait loci (QTLs) affecting spawning date and body weight in a backcross between two outbred strains of rainbow trout (Oncorhynchus mykiss). Twenty-six linkage groups were identified and synteny of duplicated microsatellite markers was used to confirm 13 homeologous chromosome pairs. Gene-centromere data were used to localize the centromeres for 13 linkage groups whose orientations were previously unknown. We applied a combination of interval mapping and single marker analysis to the segregating maternal and paternal alleles at 201 microsatellite loci. Four spawning date QTLs with suggestive evidence for an additional two QTLs were detected in female trout spawning at 3 and 4 years of age. Similarly we detected three QTLs for body weight in females at 2 years of age plus four suggestive QTLs for this trait. We found marginal evidence that three pairs of ancestral homeologues contained detectable QTLs for the same trait. In one of the three pairs of homeologues, the duplicated QTL regions mapped to the same relative chromosomal location, while the exact localization of the QTL position in one of the other pairs was difficult to infer since it was based on data from a male-derived map. The existing data were unable to refute a hypothesis that duplicated functional genes will be maintained within the telomeric regions of salmonids due to preferential male-mediated crossing over in this region. Two of the four spawning date QTLs were detected on linkage groups with unknown homeologous relationships. QTLs with possible pleiotropic effects on both spawning date and body size were localized to two linkage groups.

Animals↗

PubMedDate not supplied

Gene dosage effects on MDH isozyme expression in diploid, triploid, and tetraploid treefrogs of the genus Hyla.

Electrophoretic staining intensities at a polymorphic malate dehydrogenase locus (MDH-1) in the tetraploid treefrog Hyla versicolor and diploid Hyla chrysoscelis were compared using intraspecific and interspecific crosses. Gene dosage levels within the three ploidies were additive for the expression of isozymes encoded by this locus. Using densitometry, phenotypes from intraspecific tetraploid progeny conformed to a tetraploid gene dosage model, while phenotypes from interspecific hybrids conformed to a triploid gene dosage model. Intra- and interspecific progeny phenotypes and ratios agree with theoretical models predicting differences in such phenotypes and ratios, depending on the ploidy of the parents involved. Heterozygous phenotypes revealed that diploid crosses produced only symmetrically heterozygous progeny while tetraploid crosses produced two classes of asymmetrically heterozygous progeny in addition to symmetrically heterozygous progeny. Interspecific crosses produced only asymmetrically heterozygous progeny. Interspecific crosses involving a homozygous diploid genotype and symmetrically heterozygous tetraploid genotype produced three progeny phenotypes, while the reciprocal cross produced only two progeny phenotypes. the value of interspecific crosses between diploids and tetraploids in determining gene silencing at duplicated loci is considered.

Animals↗