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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Many diverse systems for sex determination have evolved in plants and animals. One involves physically distinct (heteromorphic) sex chromosomes (X and Y, or Z and W) that are homozygous in one sex (usually female) and heterozygous in the other (usually male). Sex chromosome evolution is thought ...
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Conservation of gene order in vertebrates is evident after hundreds of millions of years of divergence, but comparisons of the Arabidopsis thaliana sequence to partial gene orders of other angiosperms (flowering plants) sharing common ancestry ∼170–235 million years ago yield ...
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  • 3
    ISSN: 1432-1432
    Keywords: 5S rDNA ; Concerted evolution ; Gossypium ; Polyploidy ; Molecular evolution ; Genome evolution ; Repetitive DNA ; Molecular phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 5S RNA genes and their nontranscribed spacers are tandemly repeated in plant genomes at one or more chromosomal loci. To facilitate an understanding of the forces that govern 5S rDNA evolution, copy-number estimation and DNA sequencing were conducted for a phylogenetically well-characterized set of 16 diploid species of cotton (Gossypium) and 4 species representing allopolyploid derivatives of the diploids. Copy number varies over twentyfold in the genus, from approximately 1,000 to 20,000 copies/2C genome. When superimposed on the organismal phylogeny, these data reveal examples of both array expansion and contraction. Across species, a mean of 12% of nucleotide positions are polymorphicwithin individual arrays, for both gene and spacer sequences. This shows, in conjunction with phylogenetic evidence for ancestral polymorphisms that survive speciation events, that intralocus concerted evolutionary forces are relatively weak and that the rate of interrepeat homogenization is approximately equal to the rate of speciation. Evidence presented also shows that duplicated 5S rDNA arrays in allopolyploids have retained their subgenomic identity since polyploid formation, thereby indicating that interlocus concerted evolution has not been an important factor in the evolution of these arrays. A descriptive model, one which incorporates the opposing forces of mutation and homogenization within a selective framework, is outlined to account for the empirical data presented. Weak homogenizing forces allow equivalent levels of sequence polymorphism to accumulate in the 5S gene and spacer sequences, but fixation of mutations is nearly prohibited in the 5S gene. As a consequence, fixed interspecific differences are statistically underrepresented for 5S genes. This result explains the apparent paradox that despite similar levels of gene and spacer diversity, phylogenetic analysis of spacer sequences yields highly resolved trees, whereas analyses based on 5S gene sequences do not.
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  • 4
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Sir — Closely related (confamilial) genera often retain large chromosomal tracts in which gene order is co linear, punctuated by structural mutations such as inversions and translocations1. To explore the possibility that conservation of gene order might extrapolate to more distantly related ...
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The parents for the back-cross were the domestic tomato Lycopersicon esculentum cv. UC82B (denoted E) and a wild South American green-fruited tomato L. chmielewskii11 accession LA1028 (denoted CL). These strains have very different fruit masses (E - 65 g; CL - 5 g) and concentrations of soluble ...
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  • 6
    ISSN: 1572-9788
    Keywords: BAC ; positional cloning ; Sorghum propinquum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A large insert Sorghum propinquum BAC library has been constructed to analyze the physical organization of the sorghum genome and to facilitate positional cloning of sorghum genes and QTLs associated with the early stages of grain crop domestication. This library was established from 12 different ligations using high-molecular-weight DNA generated from either one cycle or two cycles of size selection. This library consists of 38 016 BAC clones with an estimated average insert size of 126 kb and coverage of 6.6 genome equivalents. The 6.6 genome-equivalent BAC library of S. propinquum provides a 99.7% probability of finding one or more BACs that contain genes of interest. Twenty mapped DNA probes, ten homologous and ten heterologous, were used to screen the library, and 121 positive clones were identified, 6.05 per locus or 6.37 per probe.
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  • 7
    ISSN: 1572-9788
    Keywords: plant breeding ; morphology ; QTL ; epistasis ; productivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The genetic basis underlying the relationship between the source leaves (the top two leaves) and the sink capacity in rice was investigated in a replicated trial of 2418 F2 derived F4 progeny from an inter-subspecific cross between cv. Lemont (japonica) and cv. Teqing (indica) and a complete linkage map with 115 well distributed RFLP markers. Path analysis indicated that 50% of the phenotypic variation in the primary sink capacity-grain weight per panicle was attributable to variation of the flag leaf area. Thirteen QTL and 30 pairs of epistatic loci were identified, which influence the length, width and area of the source leaves and the size of the primary sink (panicles) panicle length, floret density and floret number per panicle. Two QTL (QLl3b and QLw4) and 7 pairs of epistatic loci are largely responsible for the observed relationship between the source leaves and the sink capacity. The others appear to primarily influence the shape of the source leaves or panicle length/branching, and contribute little to the observed source-sink relationship and partially explain the yield component compensation. Our results suggest that important QTL affecting the source leaves can be manipulated through marker-assisted selection to increase sink capacity, which might result in improved yield potential in rice.
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  • 8
    ISSN: 1617-4623
    Keywords: Genetic mapping ; Vegetative growth ; Reproductive growth ; Pleiotropy ; Restriction fragment length polymorphism (RFLP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A segregating F2 population of Arabidopsis thaliana derived from a cross between the late-flowering ecotype Hannover/Münden (HM) and the early-flowering ecotype Wassilewskija (WS) was analyzed for flowering time and other morphological traits. Two unlinked quantitative trait loci (QTLs) affecting days to first flower (DFF-a and DFF-b) mapped to chromosome 5. QTLs which affect node number (NN), leaf length at flowering (LLF), and leaf length at 35 days (LL35) also mapped to chromosome 5; LLF-a, LL35-a, NN-a map to the same region of chromosome 5 as DFF-a; LLF-b and LL35-bmap to the same region of chromosome 5 as DFF-b. Another QTL affecting leaf length at flowering (LLF-c) maps to chromosome 3. The proximity of DFF-a, LLF-a, LL35-a and NN-a, as well as the similarity in gene action among these QTLs (additivity), suggest that they may be pleiotropic consequences of a single gene at this locus. Similarly, LL35-b and LLF-b map near each other and both display recessive gene action, again suggesting the possibility of pleiotropy. DFF-b, which also maps near LL35-b and LLF-b, displays largely additive gene action (although recessive gene action could not be ruled out). This suggests that DFF-b may represent a different gene from LL35-b and/or LLF-b. DFF-a maps near two previously identified mutants: co (which also affects flowering time and displays gene action consistent with additivity) and flc. Similar map locations and gene actions of QTLs affecting the correlated traits DFF, LLF, LL35 and NN suggest that these genomic regions harbor naturally occurring allelic variants involved in the general transition of the plant from vegetative to reproductive growth.
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  • 9
    ISSN: 1573-5028
    Keywords: evolution ; fluorescence in situ hybridization (FISH) ; genome ; repetitive DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Isolation and characterization of the most prominent repetitive element families in the genome of tetraploid cotton (Gossypium barbadense L; [39]) revealed a small subset of families that showed very different properties in tetraploids than in their diploid progenitors, separated by 1-2 million years. One element, B77, was characterized in detail, and compared to the well-conserved 5S and 45S rRNA genes. The 572 bp B77 repeat was found to be concentrated in several discontinuous tandem arrays confined to a single 550 kb SalI fragment in tetraploid cotton. Genetic mapping based on the absence of the pentameric ‘rung’ in the G. barbadense ‘ladder’ showed that B77 maps to a D-subgenome chromosome. In situ hybridization supports the contention that the array is confined largely to a single chromosomal site in the D-subgenome. The B77 repeat has undergone a substantial increase in copy number since formation of tetraploid cotton from its diploid relatives. RFLPs observed among tetraploid cotton species suggest that amplification and/or rearrangement of the repeat may have continued after divergence of the five tetraploid cotton species. B77 contains many short direct repeats and shares significant DNA sequence homology with a Nicotiana alata retrotransposon Tna1-2 integrase motif. The recent amplification of B77 on linkage group D04 suggests that the D-subgenome of tetraploid cotton may be subject to different evolutionary constraints than the D-genome diploid chromosomes, which exhibit few genome-specific elements. Further, the abundance of B77 in G. gossypioides supports independent evidence that it may be the closest extant relative of the D-genome ancestor of cotton.
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  • 10
    ISSN: 1573-5060
    Keywords: ideotype ; pleiotropy ; QTLs ; yield potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Plant type is an important composite trait associated with the yield potential in rice and other cereal crops. Several characters associated with the plant type of modern rice cultivars including tiller angle, leaf and flag leaf angle, were investigated using a complete linkage map with 115 well distributed RFLP markers and progeny testing of 2418 F2 derived F4 lines from a cross between O. sativa ssp. japonica cv. ‘Lemont’ and spp. indica cv. ‘Teqing’. One major gene (Ta) and 11 QTLs were largely responsible for the tremendous variation of the three plant type characters in the Lemont/Teqing F2 population. The major gene, Ta, located between RZ228 and RG667 on chromosome 9, accounted for 47.5% of the phenotypic variation in tiller angle and had large pleiotropic effects on both leaf and flag leaf angles. This gene plus four QTLs accounted for 69.1% of the genotypic variation in tiller angle. Eight additional QTLs for leaf and flag leaf angles were also identified, which collectively explained 52.0 and 66.4% of the genotypic variation of these traits. Ta and three QTLs ( QFla2, QFla5 and QFla7) apparently affected the related plant type characters differently, suggesting their possible differential expression in different developmental stages of rice plants or possibly clustering of different genes affecting these traits. Plant type, and consequently grain yield of rice, may be improved by deliberately manipulating these QTLs in a marker-assisted selection program.
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