Construction of a high-density linkage map and detection of sex-specific markers in Penaeus japonicus

Penaeus japonicus is one of the most important farmed shrimp species in many countries. Sexual dimorphism is observed in P. japonicus, in which females grow faster and larger than males; therefore, a unisexual female culture of P. japonicus could improve the efficiency of productivity. However, the genetic mechanisms underlying sex determination in P. japonicus are unclear. In this study, we constructed a high-density genetic linkage map of P. japonicus using genotyping-by-sequencing (GBS) technology in a full-sib family. The final map was 3,481.98 cM in length and contained 29,757 single nucleotide polymorphisms (SNPs). These SNPs were distributed on 41 sex-averaged linkage groups, with an average inter-marker distance of 0.123 cM. One haplotype, harboring five sex-specific SNPs, was detected in linkage group 1 (LG1), and its corresponding confidence interval ranged from 211.840 to 212.592 cM. Therefore, this high-density genetic linkage map will be informative for genome assembly and marker-assisted breeding, and the sex-linked SNPs will be helpful for further studies on molecular mechanisms of sex determination and unisexual culture of P. japonicus in the future.

Identification of Y chromosome markers in the eastern three-lined skink (Bassiana duperreyi) using in silico whole genome subtraction

Background

Homologous sex chromosomes can differentiate over time because recombination is suppressed in the region of the sex determining locus, leading to the accumulation of repeats, progressive loss of genes that lack differential influence on the sexes and sequence divergence on the hemizygous homolog. Divergence in the non-recombining regions leads to the accumulation of Y or W specific sequence useful for developing sex-linked markers. Here we use in silico whole-genome subtraction to identify putative sex-linked sequences in the scincid lizard Bassiana duperreyi which has heteromorphic XY sex chromosomes.

Results

We generated 96.7 × 10⁹ 150 bp paired-end genomic sequence reads from a XY male and 81.4 × 10⁹ paired-end reads from an XX female for in silico whole genome subtraction to yield Y enriched contigs. We identified 7 reliable markers which were validated as Y chromosome specific by polymerase chain reaction (PCR) against a panel of 20 males and 20 females.

Conclusions

The sex of B. duperreyi can be reversed by low temperatures (XX genotype reversed to a male phenotype). We have developed sex-specific markers to identify the underlying genotypic sex and its concordance or discordance with phenotypic sex in wild populations of B. duperreyi. Our pipeline can be applied to isolate Y or W chromosome-specific sequences of any organism and is not restricted to sequence residing within single-copy genes. This study greatly improves our knowledge of the Y chromosome in B. duperreyi and will enhance future studies of reptile sex determination and sex chromosome evolution.