斑茅割手密复合体(GXAS07-6-1)及其与甘蔗F_1的GISH分析

斑茅割手密复合体(GXAS07-6-1)是广西蔗茅属斑茅和广西甘蔗属割手密的属间杂种,聚集了双亲的优点。本研究利用基于Alu-like的PCR鉴定方法对GXAS07-6-1及甘蔗与GXAS07-6-1的3份F_1材料进行真实性鉴定,基于基因组原位杂交技术(GISH)对父本GXAS07-6-1及其3份F_1染色体组成及核型进行分析。研究结果表明:3份F_1材料为GXAS07-6-1的真杂种;父本GXAS07-6-1的染色体众数为62条,其中30条来自蔗茅属斑茅,32条来自甘蔗属割手密,核型分类属于1B,其染色体按"n+n"方式传递;GXASF_108-2-17、GXASF_108-2-22、GXASF_108-2-32的染色体数目为78~80条,其中69~71条来自甘蔗属,9~11条来自蔗茅属斑茅,3份F_1的核型分类分别属于2B、1B、1B,染色体传递方式均为"n+n"。父本GXAS07-6-1及3份F_1材料中均未发现有染色体的交换或易位现象。甘蔗与斑割复合体杂交,蔗茅属斑茅染色体在亲子间传递过程存在丢失现象。     

Generation of Y-chromosome insertions into left arm of chromosome 2 of Drosophila melanogaster

An experimental procedure describing production of insertions of Y-chromosome material into autosomes of Drosophila is presented. Irradiated Y;2 translocations served as source material. The insertion selection scheme was based on the emergence of additional progeny classes in the case of independent segregation of the detached fragments of the Y chromosome and autosome. A total of seven insertions of Y-chromosome material into the left arm of chromosome 2, specifically in regions 29F, 34A, and 36B, were obtained. All insertions were lethal in the homozygous state and caused crossing-over suppression in the left arm of chromosome 2. In addition, these mutations induced the formation of loops between the chromocenter and the region of insertion, as well as breaks in one or both homologs, which are frequently observed in preparations of polytene chromosomes. The selection scheme suggested can be used to produce insertions in any region of Drosophila melanogaster chromosomes 2 and 3, for which the Y;2 translocations exist.     

Varied expression of a Y-linked P[w+] insert due to imprinting in Drosophila melanogaster.

During gametogenesis, a gene can become imprinted affecting its expression in progeny. We have used the expression of a Y-linked P[w+]YAL transposable DNA element as a reporter system to investigate the effect of parental origination on the expression of the w+ insert. Expression of w+ was greater in male progeny when the Y chromosome, harboring the insert, was inherited from the parental male rather than from the parental female. Imprinting was not due to a genetic background influence in the males, since the only difference among the males was the parental origin of the Y chromosome. It was also observed that the genetic background can affect imprinting, since w+ expression was also higher in males when the Y was derived from C(1)DX attached-X parental females rather than from C(1)RM attached-X parental females. Though the heterochromatic imprinting mechanism is unknown, a mutated Heterochromatin Protein 1 (HP1) gene, which is associated with suppression of position-effect variegation, increases expression of the w+ locus in the P[w+]YAL insert, indicating that HP1 may play a role in Y chromosome packaging.     

A role for histone H4K16 hypoacetylation in Saccharomyces cerevisiae kinetochore function

Hypoacetylated H4 is present at regional centromeres; however, its role in kinetochore function is poorly understood. We characterized H4 acetylation at point centromeres in Saccharomyces cerevisiae and determined the consequences of altered H4 acetylation on chromosome segregation. We observed low levels of tetra-acetylated and K16 acetylated histone H4 (H4K16Ac) at centromeres. Low levels of H4K16Ac were also observed at noncentromeric regions associated with Cse4p. Inhibition of histone deacetylases (HDAC) using nicotinamide (NAM) caused lethality in cse4 and hhf1-20 kinetochore mutants and increased centromeric H4K16Ac. Overexpression of Sas2-mediated H4K16 acetylation activity in wild-type cells led to increased rates of chromosome loss and synthetic dosage lethality in kinetochore mutants. Consistent with increased H4K16 acetylation as a cause of the phenotypes, deletion of the H4K16 deacetylase SIR2 or a sir2-H364Y catalytic mutant resulted in higher rates of chromosome loss compared to wild-type cells. Moreover, H4K16Q acetylmimic mutants displayed increased rates of chromosome loss compared to H4K16R nonacetylatable mutants and wild-type cells. Our work shows that hypoacetylated centromeric H4 is conserved across eukaryotic centromeres and hypoacetylation of H4K16 at centromeres plays an important role in accurate chromosome segregation.     

Cytogenetic analysis of variegation suppressors and a dominant temperature-sensitive lethal in region 23–26 of chromosome 2L in Drosophila melanogaster

Three suppressor loci for position-effect variegation, one dominant temperature-sensitive (DTS), three Minute genes, and two recessive visible mutants (ed, tkv) have been cytogenetically localized by using duplications and deficiencies in regions 23-25 of chromosome arm 2L of Drosophila melanogaster. Two of the suppressor loci studied proved to represent haplo-abnormal genes localized in regions 23A6-23F6 and 24E2-25A1, respectively. The third one is a strong triplo-abnormal suppressor mapping in 25F4-26B9 which affects white variegation in wm4h when present in three doses. The l(2)2DTS mutation, which belongs to a group of noncomplementing dominant temperature-sensitive mutations, is localized in the 25A4-B1 region. Furthermore, two Minute genes have been localized in region 24 that are included in Df(2L)M11 and can be separated employing translocation (Y;2)P8 (24E2-4): M(2)LS2 in 24D3-4-24E2-4, and M(2)z in 24E4-5-24F5-7. A third Minute gene (M(2)S1) is localized in 25C3-8-25C9-D1. The usefulness of the isolated chromosomal rearrangements for further genetic studies of region 23-26 is discussed.     

Sex, strain, and species differences affect recombination across an evolutionarily conserved segment of mouse chromosome 16

A region of substantial genetic homology exists between human chromosome 21 (HSA21) and mouse chromosome 16 (MMU16). Analysis of 520 backcross animals has been used to establish gene order in the homologous segment. D21S16h and Mx are shown to represent the known proximal and distal limits of homology between the chromosomes, while Gap43, whose human homolog is on HSA3, is the next proximal marker on MMU16 that has been mapped in the human genome. Recombination frequencies (RFs) in four intervals defined by five loci in the HSA21-homologous region of MMU16 were analyzed in up to 895 progeny of eight different backcrosses. Two of the eight crosses were made with F1 males and six with F1 females. The average RF of 0.249 in 265 backcross progeny of F1 males was significantly higher than the 0.106 average recombination in 320 progeny of F1 females in the interval from D21S16h to Ets-2. This is in contrast to HSA21, which shows higher RFs in female meiosis in the corresponding region. Considerable variation in RF was observed between crosses involving different strains, both in absolute and in relative sizes of the intervals measured. The highest RFs occurred in a cross between the laboratory strain C57BL/6 and MOLD/Rk, an inbred strain derived from Mus musculus molossinus. RFs on this cross were nearly fivefold higher than those reported previously for an interspecific cross between C57BL/6 and Mus spretus.     

Detection of structural abnormalities in spermatozoa of a translocation carrier t(3;11)(q27.3;q24.3) by triple FISH

Structural chromosome abnormalities in spermatozoa represent an important category of paternally transmittable genetic damage. A couple was referred to our centre because of repetitive abortions and the man was found to be a carrier of a reciprocal translocation t(3;11)(q27.3;q24.3). A tailored fluorescence in situ hybridisation (FISH) approach was developed to study the meiotic segregation patterns in spermatozoa from this translocation carrier. A combination of three DNA probes was used, a centromeric probe for chromosome 11, a cosmid probe for chromosome 11q and a YAC probe for chromosome 3q. The frequency of spermatozoa carrying an abnormal chromosome constitution was compared with baseline frequencies in control semen specimens and it was found that a significantly higher percentage of spermatozoa carried an abnormal constitution for the chromosomes involved in the translocation. A normal or balanced chromosome constitution was found in 44.3% of the analysed spermatozoa, while the remainder exhibited an abnormal chromosome constitution reflecting different modes of segregation (15.9% adjacent I segregation, 6.5% adjacent II segregation, 28.9% 3 : 1 segregation, 0.8% 4 : 0 segregation, 3.6% aberrant segregation). The frequency of aneuploidy for chromosomes X, Y, 13 and 21 was assessed using specific probes but there was no evidence of interchromosomal effects or variations in the sex ratio in spermatozoa from the translocation carrier. In conclusion, structural aberrations can be reliably assessed in interphase spermatozoa using unique DNA probe cocktails, and this method provides insight into the genetic constitution of germ cells and enables evaluation of potential risks for the offspring. Received: 19 September 1997 / Accepted: 27 October 1997     

Genetic assessment of the effects of self-fertilization in a Lilium L. hybrids using molecular cytogenetic methods (FISH and ISSR)

Self-fertilization (also termed selfing) is a mode of reproduction that occurs in hermaphrodites and has evolved several times in various plant and animal species. A transition from outbreeding to selfing in hermaphroditic flowers is typically associated with changes in flower morphology and functionality. This study aimed to identify genetic effects of selfing in the F2 progeny of F1 hybrid developed by crossing Lilium lancifolium with the Asiatic Lilium hybrid ‘Dreamland.’ Fluorescence in situ hybridization (FISH) and inter-simple sequence repeats (ISSR) techniques were used to detect genetic variations in plants produced by selfing. The FISH results showed that F1 hybrid were similar to the female parent (L. lancifolium) regarding the 45S loci, but F2 individuals showed variation in the number and location of the respective loci. In F2 progeny, F2-2, F2-3, F2-4, F2-5, and F2-8 hybrids expressed two strong and one weak 5S signal on chromosome 3, whereas F2-7 and F2-9 individuals expressed one strong and two weak signals. Only two strong 5S signals were detected in an F2-1 plant. The ISSR results showed a maximum similarity value of 0.6269 between the female parent and the F2-2 hybrid. Regarding similarity to the male parent, a maximum value of 0.6119 was found in the F2-1 and F2-2 hybrids. The highest genetic distance from L. lancifolium and the Asiatic Lilium hybrid ‘Dreamland’ was observed in the F2-4 progeny (0.6352 and 0.7547, respectively). Phylogenetic relationships showed that the F2 progeny were closer to the male parent than to the female parent. Self-fertilization showed effects on variation among the F2 progeny, and effects on the genome were confirmed using FISH and ISSR analyses.     

Allelic composition and genetic background effects on transgene expression and inheritance in white clover

Allelic composition and genetic background effects on GUS expression and inheritance using a chimeric (cauliflower mosaic virus 35Sp:uidA) transgene were investigated in white clover as a prelude to transgenic cultivar development. Stable expression and Mendelian inheritance of the uidA transgene was observed over two generations when the uidA transgene was maintained in a heterozygous state. Transgenic backcross progeny (BC1) were intercrossed to produce segregating F2 populations. GUS-positive F2 plants were test-crossed with a non-transgenic control plant to determine whether individuals were heterozygous or homozygous for the transgene. Both expected and distorted segregation ratios were observed. Distortion of the segregation ratio was not caused by transgene inactivation or rearrangement, but was influenced by genetic background. BC1, BC2 and F2 populations were found to have similar levels of uidA gene expression. Quantification of GUS expression from progeny of high and low GUS expressing plants indicate that it is possible to alter transgene expression through selection. No difference was found between the level of expression for F2 plants homozygous or heterozygous for the transgene. These results indicate that F2 plants, homozygous for a transgene, might be used to develop a transgenic cultivar. However, progeny testing to determine the influence of genetic background is a prerequisite to such a development.     

Linkage relationships of seven enzyme and two pigmentation loci in the snail Biomphalaria glabrata

Crossing experiments with inbred stocks of the snail (Biomphalaria glabrata) demonstrated that variants at two loci determining pigmentation and seven enzyme-determining loci exhibited normal Mendelian segregation ratios in F2 progeny. Among 39 pairwise comparisons for joint segregation, there was evidence of genetic linkage between a locus controlling mantle pigmentation (S) and 6-phosphogluconate dehydrogenase (Pgd) and confirmation of a previously described linkage between esterase-2 (Est-2) and catalase (Cat). Recombination fractions were estimated to be 17 +/- 4 for S-Pgd and 33 +/- 5 for Est-2-Cat. The remaining five loci--Acon-1, Pgm-1, Lap-1, Lap-2, and Pgd--assorted independently. This brings to 17 the number of loci examined for segregation and assortment in this medically important species. As Biomphalaria has a chromosome number n = 18, markers should soon be available for most or all of the linkage groups.     

Inheritance of apospory in bahiagrass,Paspalum notatum

Previous studies on the inheritance of aposporous apomixis in bahiagrass showed a wide range of segregation ratios in crosses involving sexual and aposporous apomictic plants. The F1 progenies were classified through a visual progeny test carried out on few F2 plants. The number of sexual F1s highly exceeded the apomictics leading to the conclusion that apomixis was controlled by a few recessive genes. The present study examines the inheritance of apospory in bahiagrass. A sexual plant was self-pollinated and crossed with an aposporous apomictic plant as pollen donor. Backcross and F2 progenies were obtained in several combinations. All self-pollinated sexual plants or sexual x sexual crosses produced progenies free of apospory. All crosses involving a sexual and an apomictic plant produced approximately three times more apospory-free plants than plants with apospory. Bahiagrass is of autotetraploid origin and hence is expected to display tetrasomic inheritance. The most widely accepted genetic model for inheritance of apospory in tropical grasses is a single dominant gene with tetrasomic inheritance. In the present experiments none of the apospory-free F1s segregated for the apospory trait indicating that it is most likely a dominant character. However, the observed results fit better a modified model: tetrasomic inheritance of a single dominant gene with pleiotropic effect and incomplete penetrance. The excess of apospory-free plants in the F1 progeny could be ascribed to some distortion in the segregation pattern due to a pleiotropic lethal effect of the dominant A allele with incomplete penetrance. Alternatively, partial lethality of factors linked to aposporous gene may account for segregation distortion against apospory.     

Etoposide exposure during male mouse pachytene has complex effects on crossing-over and causes nondisjunction

In experiments involving different germ-cell stages, we had previously found meiotic prophase of the male mouse to be vulnerable to the induction of several types of genetic damage by the topoisomerase-II inhibitor etoposide. The present study of etoposide effects involved two end points of meiotic events known to occur in primary spermatocytes--chromosomal crossing-over and segregation. By following assortment of 13 microsatellite markers in two chromosomes (Ch 7 and Ch 15) it was shown that etoposide significantly affected crossing-over, but did not do so in a uniform fashion. Treatment generally changed the pattern for each chromosome, leading to local decreases in recombination, a distal shift in locations of crossing-over, and an overall decrease in double crossovers; at least some of these results might be interpreted as evidence for increased interference. Two methods were used to explore etoposide effects on chromosome segregation: a genetic experiment capable of detecting sex-chromosome nondisjunction in living progeny; and the use of FISH (fluorescence in situ hybridization) technology to score numbers of Chromosomes X, Y, and 8 in spermatozoa. Taken together these two approaches indicated that etoposide exposure of pachytene spermatocytes induces malsegregation, and that the findings of the genetic experiment probably yielded a marked underestimate of nondisjunction. As indicated by certain segregants, at least part of the etoposide effect could be due to disrupted pairing of achiasmatic homologs, followed by precocious sister-centromere separation. It has been shown for several organisms that absent or reduced levels of recombination, as well as suboptimally positioned recombination events, may be associated with abnormal segregation. Etoposide is the only chemical tested to date for which living progeny indicates an effect on both male meiotic crossing-over and chromosome segregation. Whether, however, etoposide-induced changes in recombination patterns are direct causes of the observed malsegregation requires additional investigation.     

Cytogenetic Analysis of Segregation Distortion in Drosophila Melanogaster: The Cytological Organization of the Responder (Rsp) Locus

The segregation distortion phenomenon occurs in Drosophila melanogaster males carrying an SD second chromosome and an SD+ homolog. In such males the SD chromosome is transmitted to the progeny more frequently than the expected 50% because of an abnormal differentiation of the SD+-bearing sperms. Three major loci are involved in this phenomenon: SD and Rsp, associated with the SD and SD+ chromosome, respectively, and E(SD). In the present work we performed a cytogenetic analysis of the Rsp locus which was known to map to the centromeric heterochromatin of the second chromosome. Hoechst- and N-banding techniques were used to characterize chromosomes carrying Responder insensitive (Rspi), Responder sensitive (Rsps) and Responder supersensitive (Rspss) alleles. Our results locate the Rsp locus to the h39 region of 2R heterochromatin. This region is a Hoechst-bright, N-banding negative heterochromatic block adjacent to the centromere. Quantitative variations of the h39 region were observed. The degree of sensitivity to Sd was found to be directly correlated with the physical size of that region, demonstrating that the Rsp locus is composed of repeated DNA.     

Instability at the k2 Mdh1-n y20 chromosomal region in soybean

Ten mutants have been reported at the k2 (tan saddle seed coat) Mdh1-n (mitochondrial malate dehydrogenase 1 null) y20 (yellow foliage) chromosomal region in soybean [Glycine max (L.) Merr.]. The precise genetic mechanism(s) responsible for generating these mutants is (are) not known. The objective of this study was to determine whether chromosomal instability exists at this region. We introduced the w4-m and Y18-m mutable systems into the three independent sources of tan saddle seed coat mutants, T239 (k2), T261 (k2 Mdh1-n), and L67-3483 (k2). A total of 12 bright yellow mutants were isolated with tan saddle seed coat, malate dehydrogenase 1 null phenotypes. Of these, 11 were found in 11 F2 mutant families out of a total of 977 derived by crossing T239 (k2), T261 (k2 Mdh1-n), and L67-3483 (k2) with six lines suspected to contain active transposable elements. One was found in the F3 generation derived from the cross A1937?×?T239 (k2). Of the 11 F2 mutant families, 10 (out of a total of 381 F2 families) were associated with the T239 (k2) genetic background, and one out of 323 was associated with the T261 (k2 Mdh1-n) genetic background. But no mutation events were found among the 273 families with the L67-3483 (k2) genetic background. Allelism and inheritance studies indicated that these 12 bright yellow mutants were new mutants in the k2 Mdh1-n y20 chromosomal region. Thus, on introducing the w4-m and Y18-m mutable systems into T239 (k2) and T261 (k2 Mdh1-n) genetic backgrounds, chromosomal instability was induced in this region. In addition, 21 greenish yellow mutants were identified in the total of 977 F2 families. All 21 greenish yellow mutants were associated with the T239 (k2) genetic background. The mutations for greenish yellow foliage affected foliage color only at the seedling stage. Cosegregation of the tan saddle seed coat character with greenish yellow foliage were observed for these 21 greenish yellow mutants, suggesting that the greenish yellow phenotype may be due to a pleiotropic effect of the k2 allele in T239 or to chromosomal rearrangements at or near the k2 allele in T239. Finally, we believe that the genetic mechanism responsible for this high frequency of instability at the k2 Mdh1-n y20 chromosomal region involves receptor element activities present at this chromosomal region, which may contain complex chromosomal rearrangements in T239 and T261.     

Molecular mapping of segregation distortion loci in Aegilops tauschii.

Distorted segregation ratios of genetic markers are often observed in progeny of inter- and intraspecific hybrids and may result from competition among gametes or from abortion of the gamete or zygote. In this study, 194 markers mapped in an Aegilops tauschii F2 population were surveyed for distorted segregation ratios. Region(s) with skewed segregation ratios were detected on chromosomes 1D, 3D, 4D, and 7D. These distorter loci are designated as QSd.ksu-1D, QSd. ksu-3D, QSd.ksu-4D, and QSd.ksu-7D. Three regions of segregation distortion identified on chromosome 5D were analyzed in two sets of reciprocal backcross populations to analyze the effect of sex and cytoplasm on segregation distortion. Extreme distortion of marker segregation ratios was observed in populations in which the F1 was used as the male parent, and ratios were skewed in favor of TA1691 alleles. There was some evidence of differential transmission caused by nucleo-cytoplasmic interactions. Our results agree with other studies stating that loci affecting gametophyte competition in male gametes are located on 5DL. The distorter loci on 5DL are designated as QSd.ksu-5D.1, QSd.ksu-5D.2, and QSd.ksu-5D.3.     

送春与多花兰种间杂交后代的ISSR分析

该文使用简单重复序列间( ISSR)分子标记,对送春与多花兰种间杂交后代进行了研究。结果表明：从80个ISSR引物中筛选出14个扩增效果稳定的ISSR引物,对两亲本和59个F1代个体进行了ISSR扩增,得到107个扩增位点,扩增的片段大小位于90~2100 bp之间,平均每个引物扩增7.64条条带,得到11种类型的带。 ISSR标记在送春×多花兰的F1代中表现出一定的多态性,分离频率为44.86％,分离位点有83.33％符合孟德尔1︰1或3︰1的分离规律,产生偏孟德尔分离的位点占12.50％,余下的4.17％属于特殊分离带型。可能导致后代变异的位点为偏孟德尔分离的6条带、缺失的8条带或新生成的2条带。聚类图中父本和母本与F1代个体间的遗传距离较远,59个杂交后代先聚集成一组,再同母本相聚为一组,最后才同父本聚在一起,59个杂种均偏母本型。送春与多花兰的杂交后代在植株形态、染色体、遗传物质方面都具备双亲特点,61个个体间的ISSR分子量标记结果和植株形态学特征都说明,59个F1代杂种包含送春和多花兰的遗传特性是真杂种;F1代杂种既有双亲的互补特征带,又有双亲的重组片断即产生新的特异带,这说明送春与多花兰的杂交后代具有遗传变异的特点。该研究结果可以有效地对杂交后代进行定向选择,为兰花的杂交育种提供了分子依据。     

Genetic analysis and molecular mapping of the avirulence gene PRE1, a gene for host-species specificity in the blast fungus Magnaporthe grisea.

We analyzed host-species specificity of Magnaporthe grisea on rice using 110 F1 progeny derived from a cross between the Oryza isolate CH87 (pathogenic to rice) and the Digitaria isolate 6023 (pathogenic to crabgrass). To elucidate the genetic mechanisms controlling species specificity in M. grisea, we performed a genetic analysis of species-specific avirulence on this rice population. Avirulent and virulent progeny segregated in a 1:1 ratio on the 2 rice cultivars 'Lijiangxintuanheigu' (LTH) and 'Shin2', suggesting that a single locus, designated PRE1, was involved in the specificity. In a combination between 'Kusabue' and 'Tsuyuake', the segregation of the 4 possible phenotypes of F1 progeny was significantly different from the expected 3:1:3:1 and instead fit a ratio of 2:0:1:1. This indicated that 2 loci, PRE1 and AVR2, were involved in specific parasitism on rice. These results suggest that the species specificity of M. grisea on rice is governed by species-dependent genetic mechanisms that are similar to the gene-for-gene interactions controlling cultivar specificity. Pathogenicity tests with various plant species revealed that the Digitaria isolate 6023 was exclusively parasitic on crabgrass. Genetic linkage analysis showed that PRE1 was mapped on chromosome 3 with respect to RAPD and SSR markers. RAPD marker S361 was linked to the avirulence gene at a distance of ~6.4 cM. Two SSR markers, m677-678 and m77-78, were linked to the PRE1 gene on M. grisea chromosome 3 at distances of 5.9 and 7.1 cM, respectively. Our results will facilitate positional cloning and functional studies of this gene.     

Mutations of the protocadherin gene PCDH15 cause Usher syndrome type 1F

Human chromosome 10q21-22 harbors USH1F in a region of conserved synteny to mouse chromosome 10. This region of mouse chromosome 10 contains Pcdh15, encoding a protocadherin gene that is mutated in ames waltzer and causes deafness and vestibular dysfunction. Here we report two mutations of protocadherin 15 (PCDH15) found in two families segregating Usher syndrome type 1F. A Northern blot probed with the PCDH15 cytoplasmic domain showed expression in the retina, consistent with its pathogenetic role in the retinitis pigmentosa associated with USH1F.     

Genetic characterization of apospory in tetraploid Paspalum notatum based on the identification of linked molecular markers

Tetraploid Paspalum notatum (bahiagrass) is a valuable forage grass with aposporous apomictic reproduction. In a previous study, we showed that apospory in bahiagrass is under the control of a single dominant gene with a distorted segregation ratio. The objective of this work was to identify molecular markers linked to apospory in tetraploid P. notatum and establish a preliminary syntenic relationship with the genomic region associated with apospory in P. simplex. A F₁ population of 290 individuals, segregating for apospory, was generated after crossing a completely sexual plant (Q4188) with a natural aposporous apomictic plant (Q4117). The whole progeny was classified as sexual or aposporous by embryo sacs analysis. A bulked segregant analysis was carried out to identify molecular markers co-segregating with apospory. Four hundred RAPD primers, 30 AFLP primers combinations and 85 RFLP clones were screened using DNA from both parental genotypes and aposporous and sexual bulks. Linkage analysis was performed with cytological and genetic information from the complete progeny. Cytoembryological analysis showed 219 sexual and 71 aposporous F₁ individuals. Seven different molecular markers (2 RAPD, 4 AFLP and 1 RFLP) were found to be completely linked to apospory. The RFLP probe C1069, mapping to the telomeric region of the long arm of rice chromosome 12, was one of the molecular markers completely linked to apospory in P. notatum. This marker had been previously associated with apospory in P. simplex. A preliminary map of the chromosome region carrying the apospory locus was constructed.     

Fine-scale genetic mapping of two Pierce’s disease resistance loci and a major segregation distortion region on chromosome 14 of grape

A refined genetic map of chromosome 14, which contains the Pierce's disease (PD) resistance locus, was created from three grape mapping populations. The source of PD resistance in these populations was b43-17, a male form of Vitis arizonica Engelm. that is homozygous resistant. The resistance locus segregated as a single dominant gene and mapped as PdR1a in the F1 selection F8909-17 (9621 population) and as PdR1b in a sibling F1 selection F8909-08 (04190 population). These two full sibs inherited either allele of the Pierce's disease resistance locus from the b43-17 parent, which is homozygous at that locus. The 9621 population consisted of 425 progeny and PdR1a mapped between markers VvCh14-56/VvCh14-02 and UDV095 within a 0.6 cM genetic distance. The 04190 population consisted of 361 progeny and PdR1b mapped between markers VvCh14-02 and UDV095/VvCh14-10 within a 0.4 cM distance. Many of the markers present on chromosome 14 were distorted with an excess of female alleles in the 04190 and 04373 population (developed from a cross of V. vinifera L. F2-35 x b43-17) indicating that potential gametophytic factors are present in this region. Common markers from this region within the 9621 population were not distorted except Scu15. When these markers were compared to V. vinifera-based maps of chromosome 14 they were also distorted suggesting the involvement of gametophytic factors, and prompting the identification of this region as Vitis-segregation distortion region 1 (V-SDR1). The refined genetic maps developed from this study can be used to identify and clone genes that confer resistance to Pierce's disease.