External links Habitat This scallop is natural to certain bays in the Southern west coast of south America, from Peru to Chile. In most growth areas, the harvesting of natural grown scallops has been replaced by aquaculture operations. The aquaculture operations consist in re-stocking the natural areas, taking care of the scallops along the grow out period and harvesting at the end of the cycle. Thanks to this practices, the natural banks have recovered and are able to maintain a sustainable production level.
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The 16 n chromosomes originating from A. The green chromosomes are from A. One chromosome from A. In these experiments, the hybrid larvae were found to be viable, whereas viable adult hybrids were not found. Yang et al. In contrast, A. The evidence based on GISH analysis provided convincing support at the cytogenetic level for the conclusion that the hybrid offspring of A.
Moreover, the amplification with ITS primers using hybrids DNA produced both parental bands, revealing that both parents had contributed to the genome composition of the hybrids. However, it should be noted that the lengths of the sequenced PP and BB ITS regions were inconsistent with the electrophoresis results, which might be attributed to different molecular configurations of the amplified ITS fragments from PP and BB during polyacrylamide gel electrophoresis.
Regardless, there is no doubt that the ITS region can play an important role in hybrid identification. The identity of adult hybrids was also demonstrated by Wang et al. In addition, cytoplasmic inheritance has been investigated using 16S rDNA, and the mode of mtDNA transmission has been shown to be matrilineal in scallops. Differing from scallops, mussels display two types of mtDNA genomes that are transmitted by males and females separately in a mode of transmission termed doubly uniparental inheritance  , .
Taken together, the F1 hybrids from A. GISH also indicated that most A. In studies of the interspecific hybridization of M. Moreover, P. Although the analysis of the genomic constitution of their hybrid larvae at early developmental stage indicated that these embryos received one haploid genome from each parent  ,  , the combination of two divergent genomes could result in genomic instability  , and the interaction of heterologous chromatin might be an important factor that leads to karyotype polymorphism in hybrid offspring .
In our study, some aneuploids and allopolyploids were observed in F1 hybrids, and the frequency of them was lower than that of the abnormal chromosomes detected in the hybrids of M. Chromosomal aneuploidy was found to be one of the most significant factors that might have a large effect on the embryo survival rate  — .
All these findings provide possible explanations for why the hybrid adults of M. Compared to these species, A. In general, distant hybridization could result in genomic changes that include alterations in gene expression, chromosomal structure and genome size  — . Sequence analysis of the ITS region in the A. These recombinant variants were most likely intermediates of the paternal ITS region undergoing gene conversion, thus indicating that some alterations occurred in the hybrid genome.
In fact, recombination intermediates have been reported for the ITS sequences of C. Although gene conversion could be bidirectional, as reported in Gossypium allopolyploid and Nicotiana allopolyploid  ,  , it was found maternally biased in the hybrids of C.
However, biased gene conversion was not found in our study because the maternal and paternal alleles were both present in the hybrid genomes and were nearly equal.
Eickbush and Eickbush  reviewed that unequal crossover has been regarded as the major mechanism for the evolution of rRNA genes.
Wang et al. In the initial formation of the hybrid, the maternal enzymatic system may treat the chromosomes of A. Specific sites in paternal recombinant regions are thus recognized by maternal endonucleases to produce double-strand breaks.
Biased gene conversion can subsequently occur when the directionality of double-strand break repair is in favor of the maternal DNA sequences. In the hybrids of A. In addition, as opposed to the biased gene conversion in the hybrid of C. Moreover, the appearance of recombinant variants in the hybrids might provide an explanation for the origin of hybrid zone novel alleles.
The AFLP analysis of the hybrid genome in our other study also revealed the occurrence of alterations, mainly involved the loss of parental AFLP loci and the gain of novel loci unpublished. These genetic variations might provide a possible basis for the heterosis observed in the A. In the GISH analysis, it was found that the fluorescence signals were not uniform among the chromosomes, with stronger signals showing banding patterns on different chromosomes Fig. GISH banding patterns were first reported by Kuipers et al.
Considering that GISH is a method primarily based on differences in repetitive sequences, stronger fluorescence signals might be initiated by uneven repetitive sequences clustering along the chromosome arms or on different chromosomes in the same cell. These regions were not effectively blocked by blocking DNA, reflecting a more rapid rate of evolution and divergence in these heterochromatin regions  and species-specific or genome-specific repetitive sequences rapidly accumulating in closely related species  , .
Huang et al. Based on the above data, we speculate that the strong GISH signals indicated heterochromatin regions across the chromosomes of A. In conclusion, our study demonstrated that the hybrids between A. The hybrid larvae possessed the expected chromosome constituents, and the hybrid adults inherited nuclear genetic material from both parents.
Cytoplasmic inheritance in scallops was found to be maternal based on the analysis of mitochondrial 16S rDNA in the hybrids. Moreover, ITS sequence analysis indicated that some variations occurred in the hybrid genomes.
This study represents the first step in analyzing the genetic basis of heterosis in these scallop hybrids. All these data could provide the theoretical foundation for further work, such as analyzing the genomic composition and genetic variation in the hybrids using the new generation of high-throughput sequencing technology, identifying the possible markers associated with heterosis and studying the coordination mechanism of hybrid genome during the combination of the two divergent genomes.
After the collection of gametes, the eggs from one species were fertilized by adding sperm from the other species to produce hybrids A. The resulting larvae were reared following routine culture procedures, as described by Zhang et al. A portion of the embryos was collected at the trochophore stage for chromosomal preparations, and adult hybrid scallops were obtained after 6 months.
The adductor muscles were removed from the living individuals and stored in liquid nitrogen until use. The ITS primers were those of Wang et al. Sequence alignments were performed using the program ClustalX 1. For the 16S rDNA analysis, all tested individuals were cloned and sequenced. The molecular diversity indices, such as polymorphic sites, transitions, transversions and indels, and the genetic distance Kimura 2-parameter among these four groups were analyzed using MEGA 3 .
The phylogenetic tree was constructed using MrBayes version 3. Briefly, the larvae were treated with colchicine 0. The total genomic DNA of A. Unlabeled blocking DNA was generated by sonicating DNA into approximately — bp fragments, which were added to the probe solution.
The hybridization signals were observed using a Nikon E epi-fluorescence microscope equipped with the appropriate filters. More than 50 spreads were examined for each sample. Supporting Information Figure S1. Electrophoreses of amplified ITS products from A. References 1. Reviews in Fish Biology and Fisheries —
Search Menu Abstract Although some external coloration and pigmentation patterns in molluscan shells may be attributable to environmental factors, most variation in these phenotypic characters depends on uncomplicated genetic mechanisms. Genetic research on inheritance of color variations in the north-Chilean scallop Argopecten purpuratus has now been expanded to analyze color segregation in juvenile scallops produced under controlled conditions employing self- and cross-fertilization. Calculations from the results were used for comparison with different numerical models based on Mendelian inheritance, and results were also obtained on the inheritance of a dorsoventral white line often observed on the left upper valve in this species. The results confirmed the hereditary basis for color variation in the shell of this scallop, suggesting a simple, dominant model of epistasis to explain the distribution of the different color variants observed purple, brown, orange, yellow, and white. The presence of the white line may be controlled by a recessive allele with simple Mendelian traits on a locus distinct from those that control color variation.
Draft genome of the Peruvian scallop Argopecten purpuratus.
Gene annotation Annotation of protein coding genes The annotation strategy for protein-coding genes integrated de novo prediction with homology and transcriptome data-based evidence. Homology sequences from African malaria mosquito Anopheles gambiae , ascidian Ciona intestinalis , Florida lancelet Branchiostoma floridae , fruit fly Drosophila melanogaster , human Homo sapiens , leech Helobdella robusta , nematode Caenorhabditis elegans , octopus Octopus bimaculoides , owl limpet Lottia gigantea , Pacific oyster Crassostrea gigas , and sea urchin Strongylocentrotus purpuratus were downloaded from Ensemble [ 21 ]. The transcriptome data were generated from adductor muscle, hepatopancreas, and mantle on Illumina HiSeq platform. Finally, we identified 26, protein-coding genes in the Peruvian scallop genome. In detail, 26, genes were predicted through the de novo method, 19, genes were annotated by RNA transcripts or raw RNA reads, and 15, genes were supported by homolog evidences. The average transcript length, CDS length, and intron length were 10, bp, 1, bp, and 1, bp, respectively Table 1.