Introduction

Genes can be duplicated through a variety of mechanisms, including whole-genome duplication (WGD), tandem duplication (TD), proximal duplication (PD), dispersed duplication (DSD), and transposed duplication (TRD). Exploring the different duplication mechanisms of gene families helps us understand the origin and evolution of the genes and provides unique insights. By identifying the types of duplication origins of cold resistance genes in plants, Song et al. found that cold resistance genes can originate from singletons, DSD, PD, TD, and/or WGD and that WGD and DSD were the major contributors to gene duplication, thus proposing the hypothesis that cold resistance genes were preferentially retained after polyploidization events [1]. Liu et al. found that both WGD and TD played an important role in the expansion of intronless genes in intron-poor subfamilies by identifying the type of origin of duplication of intron-poor and intronless family genes in plants [2]. Nezamivand‑Chegin et al. proposed that WGD or DSD types were the most frequent contributors to SPX expansion by identifying the duplication types of SPX family genes in plants [3]. Therefore, it is useful to perform an analysis of the type of duplication origin of genes in evolutionary studies of gene families.

These duplication types are recognized by the duplicate_gene_classifier program in the MCScanX package and are divided into five types: singleton, WGD, TD, PD, and DSD [4, 5]. MCScanX enforces the determination that the origin of duplication of a gene can belong to only one of the five duplication types and does not allow a gene to originate through different duplication mechanisms. However, the true meaning of a singleton, as mentioned above, is that it does not undergo duplication; i.e., it should not be called a type of duplication. There are five types of gene duplication mechanisms: WGD, TD, PD, DSD, and TRD [5, 6]. Therefore, an important duplication mode (TRD) was missing in the above studies. TRD often leads to the formation of pseudogenes, while other types of duplication lead to rapid expansion of the plant genome [1, and the numbers 1–5 are cluster IDs, which are consistent with A, B