Linkage disequilibrium ofMHC genes in the chicken

Two loci of the chicken MHC (theB complex) are expressed in erythrocytes,B-F andB-G. The former is homologous to the murineK andD loci and is also expressed in all white blood cells, while the latter is apparently restricted to RBC and is of unknown relationship toH-2 andHLA loci. A recombinant between two congenic, MHC-different strains, CB and CC, has permitted the production of antisera specific for theB-F andB-G alleles of these two strains, and these and other antisera have been used for typing of outbred populations of various chicken breeds.The cross-reactions found with haplotypes other than the donors' are extensive, sometimes even extreme, but it is possible to narrow the specificity of the typing sera by appropriate absorptions. With absorbed sera we have found a linkage disequilibrium which is almost certainly even stronger than that reported in studies of mammalianMHC loci. We have also made observations which suggest that the gametic association of a given set ofB-F andB-G alleles is probably not merely a matter of random crossing-over events.     

Genetic control of lymphocyte antigens in sheep: TheOLA complex and two minor loci

Lymphocytotoxic reagents allowed us to define 11 lymphocyte factors in sheep. After a genetic control of monospecificity had been made, a genetic study based on 400 crossings indicated that nine factors are transmitted in two haplotypes containing 0.1 or 2 factors. The linked factors of the bifactorial haplotypes are the products of two genes at two closely linked loci,OLA- A andOLA- B, having a recombination rate of about 0.6%. The nine factors are the products of fiveOLA- A and fourOLA- B alleles. Allelic frequencies at the two loci, ranging from 0.05 to 0.23 were obtained by two methods. A linkage disequilibrium between the loci is described. Among the possible causes of this, inbreeding is excluded, whereas selective pressure or more probably old fusions between sheep populations must be retained. A tenth factor (frequency 0.33 to 0.35) has a 26% recombination with OLA factors; its locus (OL-X) would be on the same chromosome but very far from theOLA complex. An 11th factor (frequency 0.30) is probably independent ofOLA; its locus (OL-Z) may be on another chromosome. The two linkedOLA loci give evidence of a major histocompatibility complex in sheep; the observed linkage disequilibrium allows one to foretell certain applications in phylogeny and perhaps in selection.     

Isolation and characterization of cadmium-resistant mutants ofAspergillus nidulans

Thirteen cadmium-resistant mutants ofAspergillus nidulans have been isolated which can grow on higher levels of cadmium than can wild-type strains. In each case, resistance results from a single gene mutation: these identify two new loci. Three mutants are located in thecadA gene on chromosome IV; the other ten have been mapped to thecadB locus, which is tightly linked to themethB gene on chromosome VI.     

Association of genetic polymorphisms with fertilization in the chicken

Summary Associations between fertilization rate and genotypes at four polymorphic loci were studied in three relatively non-inbred populations of Light Sussex chickens. In sires the genotypes tested were at theB blood-group locus only; in dams, at theB locus and three egg-white loci. Data were available for purebred matings of related substrains 6D and 6F and the ancestor strain 6 from which they were derived and for crossbred matings of 6D and 6F by two related Rhode Island Red/New Hampshire strains.In analyses of variance by dam genotypes within sires, no locus or combination of loci had a significant effect on fertilization rate. In analyses by sire and damB blood-group genotypes, no significant effects were found in 6F. SireB genotypes showed a very significant effect (P<0.001) on fertilization rate in 6D, and in 6. The latter effect was not fully acceptable since there was a significant (P<0.02) sirex damB genotypes interaction effect in 6. This interaction took the form of a lowered fertility in matings where sire and dam had the sameB genotype. The significant main effect in 6D was due to significant differences between the fertilization rates of the three most frequent sire genotypes. The same differences were not found in the other two strains. Similarly, significant sireB genotype differences in the Rhode Island Red/New Hampshire mates of 6F were not repeated in those of 6D.Combination of this result with those from our previous work with embryonic mortality in these strains is still insufficient fully to explain the continued segregation of four alleles at theB blood group locus.     

Homozygous cell typing for the rabbit RLA-D antigens in animals from commercial breeders

We have previously reported that several of theRLA haplotypes of our rabbits have anRLA-D allele in common, i. e., they fail to cross stimulate in the MLC test. To investigate the possibility that these haplotypes originated in unrelated animals, a panel of homozygous rabbits was selected to partially characterize noninbred rabbits from five commercial sources for their alleles at theRLA-D locus. In the 47 rabbits tested, 4 homozygous animals and 12 heterozygous animals were detected with the four alleles chosen for typing. At least two independent pairs of rabbits shared identicalRLA-D genotypes. Our results indicate that theRLA-D locus is not extremely polymorphic and that rabbits cannot be assumed to be completely mismatched for theRLA complex simply because they are from different breeds or from independent suppliers.     

Annual variation of enzyme polymorphism in four natural populations ofDrosophila melanogaster occupying different niches

Gene and gametic frequencies of theAdh, Aox, α-Gpdh andEst-6 loci (map position: II-50.I, III-56.6, II-20.5 and III-36.0 respectively) have been studied in two wine cellar populations at 40 km distance from each other, and two field populations, one near each of the wine cellars. Only one locus,Aox was polymorphic for more than two electromorphs. TheAdh locus seems to follow a different mode of change in genic frequencies in wine cellars, than in the field, while the other loci exhibit a similar pattern of polymorphism in the field and in the wine cellar. Linkage disequilibrium in the gameteAdh/α-Gpdh is affected by different phenomena in the field than in the wine cellar. A stronger linkage disequilibrium in theAdh/gametes observed in the field, may be a consequence of a mixture of subpopulations subjected to differential selection at theAdh locus. TheAdh locus is the only one in which selection is detected in one environment. It is neutral in other environments. Theα-Gpdh, Aox andEst-6 polymorphisms, however, behave as though they were neutral both in the wine cellar and in the field.     

Protein polymorphism and genetic divergence in slow loris (genusNycticebus)

In this study, protein electrophoresis was assayed to detect genetic variation in GenusNycticebus. A total of 29 samples (2N. coucang and 27N. pygmaeus) were analyzed for 42 genetic loci. In the 27 samples ofN. pygmaeus, 4 loci were observed to be polymerphic. Therefore, the estimatedP value (proportion of polymorphic loci) is 0.095, theA value (average number of alleles each locus) is 1.045, and theH value (mean individual heterozygosity) is 0.040. After comparing theH ofN. pygmaeus with those of other primates reported, we found that the protein variation inN. pygmaeus is slightly lower than the average level. Additionally, we also observed obivious allele difference betweenN. pygmaeus andN. coucang. There are no shared alleles between these two species in eight loci. TheNei's genetic distance between them was calculated as 0.2541, which falls in the spectrum of genetic difference between species in primates.     

Histocompatibility-2 system in wild mice

Ninety-six wild mice trapped at 13 localities in the state of Texas were tested in the dye-exclusion cytotoxic test with a battery of 49 oligospecific H-2 antisera. The antisera detected 36 class I (K and D) and 10 class II (Ia) antigens. The phenotypic frequencies of private class I antigens ranged from 1 to 20%, the majority of them being in the range between 1 and 5%. At least some of the higher frequencies resulted from the presence of more than one antibody in the typing reagents, and from other factors complicating the typing. We estimate that the frequencies of most of the class I alleles among Texas wild mice are 1% or less. This estimate leads to the prediction that at least 200 alleles exist in Texas mice at theH-2K locus, and another 200 alleles exist at theH-2D locus. Frequencies of most of the class I public antigens were in excess of 20%. In the sample of 96 mice, 46 different phenotypic combinations of private class I antigens were found, and the frequency of blanks (mice unreactive with any of the antibodies to private class I antigens) was 27%. The frequencies of private class II antigens ranged from 5 to 15%. Some of the public class II antigens, in particular those controlled by theE region, occurred with frequencies of 80% or higher. The class II antigens were found in 26 phenotypic combinations. No striking linkage disequilibrium was found either between K and D antigens, or between class I and class II antigens. The polymorphism of theK, A, andD region appears to be higher than that of the corresponding regions of the human or rat major histocompatibility complex. The polymorphism of theE region is significantly lower than that of theA, K, andD regions. The polymorphism of theA region is extensive.     

Erythrocyte antigens in Norwegian goats: serological and genetic studies.

Goat alloantisera and bovine blood typing reagents were used to characterize eight erythrocyte antigen specificities in Norwegian goats by cluster analysis, absorption and family studies. Most of the goat sera were produced by injecting dams once or twice with blood cells or blood from their own kids. The characterized specificities were designated N1-N8. The two specificities N5 and N8 were recognized both by goat alloantisera and by reagents against the bovine factors E'1 and E'2 (N5) and I (N8), which are allelic factors in the bovine B-system. In goat families, the two specificities also behaved as alleles. Consequently, the locus or gene system coding for these specificities was called the B-system of goats. The six other erythrocyte antigens were provisionally assigned to six separate loci. In addition, a bovine anti-sheep R factor reagent reacted with cells from 3.3% of the goats tested, whereas a monoclonal antibody against the Forssman antigen reacted with all the goats tested.     

Immunogenetic studies of rhesus monkeys

Five alloimmune blood typing reagents have been produced which define five new blood group systems in rhesus monkeys. Each of the five independent blood group loci is comprised of a detectable allele and a null allele. Using these new reagents and those previously described, we can potentially identify close to a million phenotypes in rhesus monkeys.     

Molecular genetic analysis of theripening-inhibitor andnon-ripening loci of tomato: A first step in genetic map-based cloning of fruit ripening genes

Ripening represents a complex developmental process unique to plants. We are using tomato fruit ripening mutants as tools to understand the regulatory components that control and coordinate the physiological and biochemical changes which collectively confer the ripe phenotype. We have genetically characterized two loci which result in significant inhibition of the ripening process in tomato,ripening-inhibitor (rin), andnon-ripening (nor), as a first step toward isolating genes likely to encode key regulators of this developmental process. A combination of pooled-sample mapping as well as classical restriction fragment length polymorphism (RFLP) analysis has permitted the construction of high-density genetic maps for the regions of chromosomes 5 and 10 spanning therin andnor loci, respectively. To assess the feasibility of initiating a chromosome walk, physical mapping of high molecular weight genomic DNA has been employed to estimate the relationship between physical distance (in kb) and genetic distance (in cM) around the targeted loci. Based on this analysis, the relationship in the region spanning therin locus is estimated to be 200–300 kb/cM, while thenor locus region ratio is approximately 200 kb/1 cM. Using RFLP markers tightly linked torin andnor, chromosome walks have been initiated to both loci in a yeast artificial chromosome (YAC) library of tomato genomic DNA. We have isolated and characterized several YAC clones linked to each of the targeted ripening loci and present genetic evidence that at least one YAC clone contains thenot locus.     

A polymorphism detected in a variable number of tandem repeats (VNTR) of the seminal vesicle secretion (SVS) IV gene in inbred rats

The second intron of the rat SVS IV gene contains a tandem repeat region of 20-bp sequences. This region was amplified using the polymerase chain reaction to detect variations. Three alleles, characterized by amplified fragments of 750, 490, and 390 bp, respectively, were found in 24 strains examined. This variation segregated in F₁ and backcross progeny in an autosomal codominant manner. We tentatively designated this locusSvs-4. Analysis of linkages between theSvs-4 locus and other loci revealed that it was closely linked to theSvp-1 (<2.9%) and the a (10.0±6.7%) loci, which belong to rat linkage group IV. TheSvp-1 andSvs-4 loci, however, were differently distributed among the inbred rat strains.This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan.     

The nematode-resistance gene,<Emphasis Type="Italic"> Mi-1</Emphasis>, is associated with an inverted chromosomal segment in susceptible compared to resistant tomato

The gene Mi-1 confers effective resistance in tomato (Lycopersicon esculentum) against root-knot nematodes and some isolates of potato aphid. This locus was introgressed from L. peruvianum into the corresponding region on chromosome 6 in tomato. In nematode-resistant tomato, Mi-1 and six homologs are grouped into two clusters separated by 300 kb. Analysis of BAC clones revealed that the Mi-1 locus from susceptible tomato carried the same number and distribution of Mi-1 homologs, as did the resistant locus. Molecular markers flanking the resistant and susceptible loci were in the same relative orientation, but markers between the two clusters were in an inverse orientation. The simplest explanation for these observations is that there is an inversion between the two clusters of homologs when comparing the Mi-1 loci from L. esculentum and L. peruvianum. Such an inversion may explain previous observations of severe recombination suppression in the region. Two Mi-1 homologs identified from the BAC library derived from susceptible tomato are not linked to the chromosome 6 locus, but map to chromosome 5 in regions known to contain resistance gene loci in other solanaceous species.Communicated by J.S. Heslop-Harrison     

Three new blood groups of rhesus monkeys

Three new blood group systems, called “T,” “U,” and “V,” have been identified in the rhesus monkey (Macaca mulatta). Each system consists of a single antigenic factor (blood group) detected by a monospecific alloimmune reagent that agglutinates erythrocytes. The antisera that detect these blood groups were obtained following a series of alloimmunizations and absorption fractionizations of the resulting antisera to produce operationally monospecific typing reagents. Analyses of family data indicated that each blood group was controlled by an autosomal dominant gene and that each system was independent of previously defined systems. With the addition of these new blood groups, we can identify 16 different blood group systems and well over one hundred million possible phenotypes in this species.     

Restimulation in secondary MLC by a non-D-locus determinant within the MHC

By testing a family in which one offspring had inherited a chromosome including a recombination between theHLA-B andD loci, we sought to obtain some insight into whether determinants other than those atHLA-D are capable of restimulating in a secondary MLC. Results obtained in the primary MLC indicated that the recombinant child did not express products of theHLA-D region normally associated with this haplotype. When sensitization in a primary MLC was to the entire haplotype, everyone who had the sensitizing haplotype restimulated strongly and specifically. In addition, however, weak to moderate stimulation was obtained when the cells of the recombinant child were used to restimulate. Presumably these cells possessed determinants coded for within theHLA-A toB chromosomal segments of the sensitizing haplotype, but not those coded for by theHLA-D locus. Our results indicate that a simple structure atHLA-D is not the sole factor in the secondary MLC. Either the products of loci outside theHLA-D locus can also restimulate or the recombination occurred within theD locus, suggesting that theD region contains more than one locus coding for restimulating determinants.     

Rapid typing of HLA-DQB1 DNA polymorphism using nonradioactive oligonucleotide probes and amplified DNA

The allelic sequence diversity at theHLA-DQBI locus has been analyzed by polymerase chain reaction (PCR) amplification and sequencing. Fifteen amino acid sequence-defined alleles (one previously unreported) and several silent nucleotide polymorphisms which subdivide these alleles have been identified. Here, we describe the specific amplification of theDQB1 second exon by several different PCR primer pairs and a simple and rapid typing procedure using a panel of 16 horseradish peroxidase (HRP)-labeled oligonucleotide probes capable of distinguishing theseDQBI alleles.     

Linkage in mice of genes controlling an immunoglobulin kappa-chain marker and the surface alloantigen Ly-3 on T lymphocytes

Evidence obtained using recombinant inbred and congenic mouse strains has shown that thePC8 locus responsible for determining a marker on a singlek chain in inbred mice is linked to theLy-2,3 locus on chromosome 6. The upper limit of the map distance between these loci is approximately three centimorgans. This finding is discussed in relation to other known light-chain variants that are associated with theLy-2,3 locus.Abbreviations used in this paper are as follows L light chains - PC phosphocholine - H8 HOPC 8 - IEF isoelectric focusing - KLH keyhole limpet hemocyanin - RI recombinant inbred     

Nitrate reductases inEscherichia coli

Escherichia coli expresses two different membrane-bound respiratory nitrate reductases, nitrate reductase A (NRA) and nitrate reductase Z (NRZ). In this review, we compare the genetic control, biochemical properties and regulation of these two closely related enzyme systems. The two enzymes are encoded by distinct operons located within two different loci on theE. coli chromosome. ThenarGHJI operon, encoding nitrate reductaseA, is located in thechlC locus at 27 minutes, along with several functionally related genes:narK, encoding a nitrate/nitrite antiporter, and thenarXL operon, encoding a nitrate-activated, two component regulatory system. ThenarZYWV operon, encoding nitrate reductase Z, is located in thechlZ locus located at 32.5 minutes, a region which includes anarK homologue,narU, but no apparent homologue to thenarXL operon. The two membrane-bound enzymes have similar structures and biochemical properties and are capable of reducing nitrate using normal physiological substrates. The homology of the amino acid sequences of the peptides encoded by the two operons is extremely high but the intergenic regions share no related sequences. The expression of both thenarGHJI operon and thenarK gene are positively regulated by two transacting factors Fnr and NarL-Phosphate, activated respectively by anaerobiosis and nitrate, while thenarZYWV operon and thenarU gene are constitutively expressed. Nitrate reductase A, which accounts for 98% of the nitrate reductase activity when fully induced, is clearly the major respiratory nitrate reductase inE. coli while the physiological role of the constitutively expressed nitrate reductase Z remains to be defined.Abbreviations NR nitrate reductase On leave from Department of Biochemistry and Molecular Biology, The University of Texas Medical school at Houston, Houston, Texas, 77225, USA     

Inheritance and molecular mapping of two fertility-restoring loci for Honglian gametophytic cytoplasmic male sterility in rice (<Emphasis Type="Italic">Oryza sativa </Emphasis>L.)

The Honglian cytoplasmic male sterility (cms-HL) system, a novel type of gametophytic CMS in indica rice, is being used for the large-scale commercial production of hybrid rice in China. However, the genetic basis of fertility restoration (Rf) in cms-HL remains unknown. Previous studies have shown that fertility restoration is controlled by a single locus located on chromosome 10, close to the loci Rf1 and Rf4, which respond to cms-BT and cms-WA, respectively. To determine if the Rf locus for cms-HL is different from these Rf loci and to establish fine-scale genetic and physical maps for map-based cloning of the Rf gene, high-resolution mapping of the Rf gene was carried out using RAPD and microsatellite markers in three BCF₁ populations. The results of the genetic linkage analysis indicated that two Rf loci respond to cms-HL, and that these are located in different regions of chromosome 10. One of these loci, Rf5 , co-segregates with the SSR marker RM3150, and is flanked by RM1108 and RM5373, which are 0.9 cM and 1.3 cM away, respectively. Another Rf locus, designated as Rf6(t), co-segregates with RM5373, and is flanked by RM6737 and SBD07 at genetic distances of 0.4 cM. The results also demonstrated these loci are distinct from Rf1 and Rf4. A 105-kb BAC clone covering the Rf6(t) locus was obtained from a rice BAC library. The sequence of a 66-kb segment spanning the Rf6(t) locus was determined by a BLASTX search in the genomic sequence database established for the cultivar 93-11.Communicated by R. Hagemann     

A map of barley chromosome 2 using isozymic and morphological markers

The F₂ progeny of a cross between a chromosome 2 multiple marker stock and an adapted cultivar of barley were analyzed for four morphological markers and electrophoretic patterns of eight leaf isozymes. TheIdh-2 locus was linked to thePer-5 locus (27.96±5.07 cM) and to thee locus (10.26±3.13 cM). Also, thePer-5 ande loci were located on the short arm of chromosome 2. In additionIdh-2 was also located on barley chromosome 2 and was linked to thev locus (13.18±3.56 cM), which is located on the long arm of chromosome 2. Two other marker genes,li andwst,,B, were linked (26.50±5.24 cM) on chromosome 2 but segregate independently of the other loci evaluated. This project was supported by funds from the U.S.-Spain Joint Committee for Scientific and Technological Cooperation.