Preliminary evidence of segregation distortion in the SLA system

The segregation of 11 well-defined SLA haplotypes was investigated in 40 Land-race and 48 Large White Danish and Swiss litters. Among the 11 haplotypes, the segregation of one (SLA 20-8.2.11) deviated significantly from the expected 1:1 segregation ratio in back-cross families. Tests indicated that these families were homogeneous with respect to segregation distortion, although the distortion was more pronounced in litters sired by heterozygous Danish boars than by heterozygous Swiss boars and Danish and Swiss sows. The data presented do not allow any definite conclusion about the cause of the segregation distortion. The possibility of the distortion being caused either by a complex similar to the T/t-complex found in mouse and contemplated in man or directly by the SLA region is discussed.     

The swine histo compatibility system SLA: serological studies in the common Swiss and Danish swine breeds

Alloantisera were produced in common Swiss and Danish swine breeds by immunization with leucocytes or skin-grafts. Out of the 126 antisera, 66 were chosen for further study based on titrations employing lymphocytes from unrelated pigs typed with French SLA antisera (Vaiman, Chardon & Renard, 1979). The 66 selected antisera and the French reagents defining 26 SLA specificities were used to type lymphocytes from 595 unrelated pigs of the common Swiss and Danish breeds. The reaction-patterns of the French, Swiss and Danish antisera were adequately correlated for the French SLA specificities Nos FJ 2, 3, 6, 7, 8, 9, 11, 14, 19, 20 and 24 and for the haplotypes FJ 15.1.18 and FJ 5.4. In addition, a cluster of correlated Danish and Swiss antisera characterized a new specificity, provisionally designated CPH 31. This specificity was frequent in the Danish Landrace pigs.
Using the reagents identified in this report, the segregation of SLA markers was studied. Back-cross families demonstrated segregation of 15 distinct SLA haplotypes of which 14 are common in French Landrace or Large White. Differences were found in haplotype frequencies in both the Swiss and the Danish Landrace and Large White breeds.     

杂种偏分离的遗传和分子机理研究进展

杂种偏分离是指杂交后代群体在某个位点的基因型分离比偏离了预期的孟德尔分离比例的一种现象,是来自不同杂交亲本基因之间的不兼容性所致。功能缺失型和功能获得型的基因间互作都可以导致杂种偏分离,其中前者的机理比较简单,即缺陷型的基因组合导致原有功能丧失而造成细胞死亡。功能获得型杂种偏分离系统是由多基因控制的遗传系统,包含两个基本成分：杀手(killer)因子和护卫(protector)因子,此外还有增强子(enhancer)、抑制基因(repressor)等修饰因子。功能获得型杂种偏分离有通用的遗传模型：具有传递优势的单倍型含有高活性的killer+和protector+;传递劣势的单倍型含有低活性的killer-和protector-;中性的单倍型(广亲和型)则含有killer-和protector+。该系统通过killer和protector间的紧密连锁、修饰因子的积累等途径得以在自然选择中保存下来。尽管不同功能获得型杂种偏分离系统的遗传机理有较高的相似性,但分子机制则大相径庭。文章综述了杂种偏分离的遗传和分子机理以及其与杂种不育的关系,以期为后续杂种偏分离研究提供参考。     

A comparison of bovine lymphocyte antigens

In Canberra, 31 antigens have been described on the surface of bovine lymphocytes. Seven antigens are subgroups of other antigens. Eleven antigens are similar to the eleven antigens which have been described in Melbourne. Fourteen antigens are similar to twelve international-workshop antigens and two European-workshop antigens.     

Genetic variability at the pig SLA complex in U.S. breeds of pigs1

Lymphocytes from 90 mature pigs and 548 growing pigs from 6.5 litters were screened with cytotoxic antibodies against swine lymphocyte antigens. Pigs included in the survey were from the Chester White, Duroc, Hampshire, Landrace and Yorkshire breeds. Significant differences between breeds were found in the frequency of the three haplotypes tested. Such differences may provide the genetic variability needed to determine associations between disease susceptibility and the pig's major histocompatibility gene complex.     

Selection and segregation distortion in a sex-differentiated population

We extend the classical model for selection at an autosomal locus in a sex-differentiated population to include segregation distortion. The equations remain the same, but the fitness parameters are interpreted differently and refer to alleles instead of genotypes. We derive conditions for internal and external stability of the equilibria, i.e., stability with respect to perturbations of alleles that are already present at equilibrium and stability with respect to invasion attempts by newly arising alleles. We show that, in a sex-differentiated population, external stability of an equilibrium can be judged on the basis of Shaw--Mohler criteria. Throughout, we compare the situation in populations with and without sex differentiation. Interestingly, internal stability is more difficult to achieve in a population without sex differentiation than in a population in which selection and segregation distortion are restricted to one sex. In a companion paper we show how the general results of the present paper can lead to new insights into specific systems such as the t complex of the house mouse.     

Common features of segregation distortion in plants and animals

Segregation distortion is increasingly recognized as a potentially powerful evolutionary force. This runs counter to the perception that non-Mendelian genes are rare genetic curiosities, a view that seems to be supported by the near ubiquity of the Mendelian system of inheritance. There are several reasons why segregation distortion may be more important than is evidenced by known empirical examples. One possibility is that the types of segregation distorters we have found are only a subset of a broader range of non-Mendelian systems, many of which go undetected. In this paper, we review what is known about the sex-linked meiotic drive system in the plant, Silene latifolia, and present some data on the mechanism of segregation distortion. We outline the general features that segregation distorters in plants and animals have in common. In some cases, such as the paucity of systems that directly alter meiotic segregation, there are likely to be inherent constraints on the range of systems that can possibly occur. Other generalities, however, support the notion that many forms of meiotic drive are possible, and that the known examples of segregation distortion are likely to be only subset of those that can possibly occur. Non-Mendelian genes may therefore have greater evolutionary importance than their current abundance in nature would suggest.     

The pig histocompatibility system SLA: Serological study on a group of antigenic specificities

The report presents an analysis of a group of class I SLA reagents which were highly correlated within one cluster in a previous analysis. Further population and family studies, and selected purification of several of these reagents led to the identification of 4 distinct specificities, namely SLA A 15, B 18, C 1 and A 16. Three of them, SLA A 15, B 18 and C 1, are actually in strong linkage disequilibrium and represent the main SLA haplotype in the Large White breed. SLA A 16 is present essentially in the Landrace breeds. SLA A 16 displays a strong cross-reaction with SLA A 15 and there is another specificity in linkage disequilibrium with SLA A 16 which cross-reacts with SLA B 18. Altogether, the strong linkage disequilibrium and the high degree of cross-reactivity among the allelic products of the SLA complex explain the failure to detect the diversity of our reagents in previous studies.     

Analysis of segregation distortion and association of the bovine FGF2 with fertilization rate and early embryonic survival

Fibroblast growth factor 2 ( FGF2 ) plays an important role in fertility and early embryo development. The objectives of this study were to test the association of FGF2 polymorphisms with fertilization success in cattle using an in vitro fertilization experimental system and to investigate the mechanisms leading to the presence of rare alleles of FGF2 in the Holstein population. A total of 7502 fertilizations were performed and a total of 5049 embryos were produced to collect fertilization and embryo survival records. A total of 444 ovaries, from which oocytes were aspirated and fertilized, were genotyped for two single nucleotide polymorphisms (SNPs) previously identified in FGF2 (g.23G>T and g.11646A>G). Frequency of the TT genotype of the g.23G>T SNP was low in the ovary population (5.4%) and in a different Holstein cattle population (6.6%) examined in this study. Single SNP analysis showed that both SNPs were associated with early embryonic survival rate. Two-way interaction analysis revealed significant association of epistatic interaction between the SNPs with fertilization rate. To test whether or not low frequency of allele T for the g.23G>T SNP in the population is a result of a fertilization failure of T oocytes, semen from six GG bulls was used to fertilize a total of 458 oocytes obtained from 19 GT ovaries. A significant segregation distortion was observed for 169 embryos genotyped for the g.23G>T SNP. We conclude that oocytes carrying the T allele show a reduced fertilization rate and that segregation distortion leads to rarity of the TT genotype in the population.     

Genetic and other effects on antibody and cell mediated immune response in swine leucocyte antigen (SLA)-defined miniature pigs

Summary. Miniature pigs of eight swine leucocyte antigens (SLA) haplotypes were immunized with sheep erythrocytes (SRBC), hen egg white lysozyme (HEWL) and the synthetic peptide (T, G)-A–L to induce antibody. Bacillus Calmette Geurin (BCG) and dinitrochlorobenzene (DNCB) were used to induce cell mediated immune response (CMI). Analysis of variance by least squares was used to assess the effects of SLA haplotype, sire, dam, litter and sex of pig on the magnitude of the primary and secondary antibody response and on dermal delayed type hypersensitivity induced by purified protein derivative of tuberculin (PPD) and DNCB-induced contact hypersensitivity.
The statistical model accounted for 43.50–77.30% of the observed variability in antibody and CMI at various times after immunization or challenge. While SLA had a significant effect on both antibody and CMI to some antigens at some, but not all times, sire, dam and litter were more frequently significant and to a greater degree.
Haplotypes dd, dg and gg produced more antibody to SRBC and (T, G)-A–L while dg and gg had higher primary, but not secondary antibody response to HEWL. Delayed hypersensitivity to PPD was most marked in pigs of dd, dg and gg haplotypes while contact hypersensitivity to DNCB was expressed least in the dg and gg haplotype pigs.
Heritability estimates were high for response to (T, G)-A–L and HEWL indicating feasibility of selective breeding for these traits.     

Transmission of male recombination,segregation distortion and sex-ratio imbalance inDrosophila melanogaster

From the first test cross progenies of control (no larval transfers; no ethyl methanesulphonate), physical stress (two larval transfers; no ethyl methanesulphonate) and 0.75% ethyl methanesulphonate (two larval transfers; 0.75% ethyl methanesulphonate)-treated F₁ (Oregon K +/dumpy black cinnabar, dp b cn) males ofDrosophila melanogaster, respectively, 6,10 and 52 wild-looking first test cross males were again test crossed to obtain second generation. The overall percentages of male recombination detected in the second test cross progenies, in the three sets of experiments, were statistically the same as those in the first test cross progenies. Thus the enhanced male recombination caused by physical stress (with or without ethyl methanesulphonate) was transmitted to next generation. Non-reciprocal male recombination was observed indp b but not inb cn region in both first and second test cross progenies. Three abnormalities, (i) production of wild-type flies in majority overdp b cn type, (ii) Non-Mendelian segregation atdp b andcn loci and (iii) sex-ratio differences fordp bcn and +b cn types observed in test cross progenies of F₁ males ofDrosophila melanogaster were transmitted to next generation when induced with 0.75 % ethyl methanesulphonate but not when these abnormalities were induced with physical stress. The data suggest possible association of non-reciprocal male recombination, segregation distortion and sex-ratio imbalance inDrosophila melanogaster. In fact these may be representing different aspects of the same phenomenon     

An informative linkage map of soybean reveals QTLs for flowering time, leaflet morphology and regions of segregation distortion.

A genetic linkage map covering a large region of the genome with informative markers is essential for plant genome analysis, including identification of quantitative trait loci (QTLs), map-based cloning, and construction of a physical map. We constructed a soybean genetic linkage map using 190 F2 plants derived from a single cross between the soybean varieties Misuzudaizu and Moshidou Gong 503, based on restriction-fragment-length polymorphisms (RFLPs) and simple-sequence-repeat polymorphisms (SSRPs). This linkage map has 503 markers, including 189 RFLP markers derived from expressed sequence tag (EST) clones, and consists of 20 major linkage groups that may correspond to the 20 pairs of soybean chromosomes, covering 2908.7 cM of the soybean genome in the Kosambi function. Using this linkage map, we identified 4 QTLs--FT1, FT2, FT3, and FT4--for flowering time, the QTLs for the 5 largest principal components determining leaflet shape, 6 QTLs for single leaflet area, and 18 regions of segregation distortion. All 503 analyzed markers identified were located on the map, and almost all phenotypic variations in flowering time were explained by the detected QTLs. These results indicate that this map covers a large region of the soybean genome.     

The Cell Biology of Antigen Processing

Abstract

T lymphocytes recognize antigen only after a series of intracellular events known as antigen processing. The result of antigen processing is the production of short segments of the primary peptide sequence bound to a polypeptide-binding groove on major histo compatibility complex (MHC) molecules. Antigen originates from one of two sites: intracellular or extra cellular. There are two corresponding pathways for antigen processing and two corresponding classes of MHC molecule. Analysis of each pathway has demonstrated that their separation is not purely anatomical, but is maintained by molecular interactions with other molecules. Antigen processing has been shown to regulate the overall immune response, but the mechanisms involved remain obscure.     

Sequence-based evidence for major histocompatibility complex-disassortative mating in a colonial seabird

The major histocompatibility complex (MHC) is a polymorphic gene family associated with immune defence, and it can play a role in mate choice. Under the genetic compatibility hypothesis, females choose mates that differ genetically from their own MHC genotypes, avoiding inbreeding and/or enhancing the immunocompetence of their offspring. We tested this hypothesis of disassortative mating based on MHC genotypes in a population of great frigatebirds (Fregata minor) by sequencing the second exon of MHC class II B. Extensive haploid cloning yielded two to four alleles per individual, suggesting the amplification of two genes. MHC similarity between mates was not significantly different between pairs that did (n = 4) or did not (n = 42) exhibit extra-pair paternity. Comparing all 46 mated pairs to a distribution based on randomized re-pairings, we observed the following (i): no evidence for mate choice based on maximal or intermediate levels of MHC allele sharing (ii), significantly disassortative mating based on similarity of MHC amino acid sequences, and (iii) no evidence for mate choice based on microsatellite alleles, as measured by either allele sharing or similarity in allele size. This suggests that females choose mates that differ genetically from themselves at MHC loci, but not as an inbreeding-avoidance mechanism.     

Uneven segregation of sporophytic self-incompatibility alleles in Arabidopsis lyrata

Self-incompatibility in Arabidopsis lyrata is sporophytically controlled by the multi-allelic S-locus. Self-incompatibility alleles (S-alleles) are under strong negative frequency dependent selection because pollen carrying common S-alleles have fewer mating opportunities. Population genetics theory predicts that deleterious alleles can accumulate if linked to the S-locus. This was tested by studying segregation of S-alleles in 11 large full sib families in A. lyrata. Significant segregation distortion leading to an up to fourfold difference in transmission rates was found in six families. Differences in transmission rates were not significantly different in reciprocal crosses and the distortions observed were compatible with selection acting at the gametic stage alone. The S-allele with the largest segregation advantage is also the most recessive, and is very common in natural populations concordant with its apparent segregation advantage. These results imply that frequencies of S-alleles in populations of A. lyrata cannot be predicted based on simple models of frequency-dependent selection alone.     

cDNA cloning and genetic polymorphism of the swine major histocompatibility complex (SLA) class II DMA gene

cDNA clones corresponding to the swine histocompatibility complex (SLA: swine leucocyte antigen)-DM alpha chain were isolated using the polymerase chain reaction (PCR) products from the third exon in the human HLA-DMA gene as a probe. Amino acid comparative analysis revealed that these clones were more closely related to the bovine and human DMA genes than to the other swine class II genes alpha chain genes, DRA, DQA and DOA. These results suggest that the SLA-DMA gene is expressed and may function, like HLA-DM, as an important modulator in class II restricted antigen processing in swine. Furthermore, based on the sequences and PCR-restriction fragment length polymorphism (PCR-RFLP) patterns in the SLA-DMA gene, no allelic variation was recognized in the second exon, but five allelic variations were recognized in the third exon in five different breeds of swine. These DMA alleles were defined by variation at four nucleotide positions. Two of these alleles resulted in an amino acid substitution. These results suggest that SLA-DMA has little polymorphism as observed in HLA-DMA and mouse H2-Ma.     

Influence of epistatic segregation distortion loci on genetic marker linkages in Japanese flounder

For genetic linkage analysis of Japanese flounder, 160 doubled haploids (DH) were artificially produced using mitotic gynogenesis and were genotyped for 458 simple sequence repeat (SSR) markers, 101 of which show distortional segregation. The genetic linkage map was constructed by modifying recombination fractions between the distorted markers. Between the corrected and uncorrected genetic maps, there were considerable differences in genetic distance, but not in relative locations among markers. Using a liability model, a segregation distortion locus (SDL), with an additive genetic effect of 1.772, was mapped between markers BDHYP387 and Poli56TUF of chromosome 24 in the corrected genetic map. Additionally, six pairs of epistatic SDLs were identified on chromosomes 1, 5, 8, 9, 23, and 24. Changes in genetic distances between markers did not occur on chromosome regions with main effect SDLs. However, most chromosome regions where genetic distances changed covered the detected epistatic SDLs. This study concluded that epistatic SDLs decrease linkages between markers and lengthen genetic distances in Japanese flounder. This finding has been partially validated in other DH populations derived from three female Japanese flounders.     

Identification and characterization of segregation distortion loci along chromosome 5B in tetraploid wheat

Segregation distortion genes are widespread in plants and animals and function by their effect on competition among gametes for preferential fertilization. In this study, we evaluated the segregation distortion of molecular markers in multiple reciprocal backcross populations derived from unique cytogenetic stocks involving the durum cultivar Langdon (LDN) and wild emmer accessions that allowed us to study the effects of chromosome 5B in isolation. No segregation distortion of female gametes was observed, but three populations developed to analyze segregation of male gametes had genomic regions containing markers with skewed segregation ratios. One region of distortion was due to preferential transmission of LDN alleles over wild emmer alleles through male gametes. Another region required the presence of LDN 5B chromosomes in the female for preferential fertilization by male gametes harboring LDN alleles indicating that the corresponding genes in the female gametes can govern genes affecting segregation distortion of male gametes. A third region of distortion was the result of preferential transmission of wild emmer alleles over LDN alleles through male gametes. These results indicate the existence of different distorter/meiotic drive elements among different genotypes and show that distortion factors along wheat chromosome 5B differ in chromosomal location as well as underlying mechanisms.