I'm not sure I understand your follow-up question. N2 is the C. elegans reference strain so, of course, what's released by Wormbase is the N2 sequence. I think you have to understand that published reference genomes are not a static thing, but undergoing curation and corrections, meaning there exact nucleotide sequence can change. When that happens UCSC assigns a new ce version number. Wormbase on the other hand is a database that includes way more than just the reference genome sequence (protein sequences, genome annotations, etc.) and these other things typically change much faster than the reference sequence. That's why Wormbase releases (with new WS version numbers) are quite frequent, but not every one of them brings an actual change to the reference genome sequence (e.g., WS190 was ce6, but between WS190 and WS199 the reference sequence didn't change). Anyway, all these versions are N2 sequences (just at different levels of accuracy or correctness, if you will).
Thanks for your sincere help . It means a lot to me.And there are still some questions remain to me. Firstly,I thought WS220/ce10 refers to the genome of CB4856,but i am not sure . And i need the genome of N2 to be the reference genome in my analysis .So i wonder if the latest version of N2 genome is the best choice for me. Thirdly,what is function of the HA_SNPS_Unfiltered_112061Variants_WS220.64_chr.vcf file in the analysis of WGS? I will appreciate it if you can give me some suggestion .