Some new terms for duplicated genes

If we are to investigate the relationships between genes, which can involve complex combinations of duplication, deletion and speciation, we need precise terminology. The terms 'paralogy' and 'orthology' have proved very useful in distinguishing two different relationships between homologous genes. Some relationships, however, are not included in either of these terms. I propose three new terms, for use in situations in which one or both lineages that lead to two present-day genes involve gene duplications.