In-Paralog

Diagram depicting evolutionary relationship between orthologs, in-paralogs and out-paralogs

In-paralogous genes are essentially paralogous genes. The nomenclature helps in distinguishing different classes of genes derived from the divergence of lineages (aka events leading to speciation) and the duplication within a lineage when multiple taxa are compared. Specifically, in helps identify cases where two lineages share a gene duplication, but each lineage loses the reciprocal paralog. These genes may be mistakenly be called orthologs when they are out-paralogs.