HSA 1/2/8/20 paralogon Co-duplicated groups
It was proposed that elucidation of intra-genomic syntenic regions through map self-comparison approach does not provide compelling support for the proposed mechanism of origin of paralogons (Abbasi, 2008). To present a plausible explanation of the evolutionary events that shaped the syntenic relationships seen on present day human 1/2/8/20 paralogon bearing chromosomes, topology comparison approach was employed for triplicated/quadruplicated gene families residing on this paralogon (Abbasi, 2010b; Abbasi and Grzeschik, 2007; Zhang and Nei, 1996). Gene families belonging to a particular co-duplicated group suggest that they share similar evolutionary history and might have originated through gene cluster duplication event, whereas genes belonging to different co-duplicated groups may not share their evolutionary history and might not have duplicated simultaneously. Duplication history summary of families residing on HSA:1/2/8/20 paralogon with respect to speciation events and identified co-duplication events are given in the following table.
| Chromosomes/Paralogon | |||||||
| Name of Co-duplicated group | Co-duplicated Group A | Co-duplicated Group B | Co-duplicated Group C | Co-duplicated Group D | Remaining Families | Largely duplicated in invertebrates (prior to vertebrate invertebrate split) | Total |
| No. of gene families | 2 | 3 | 6 | 6 | 9 | 10 | 36 |
For 36 multigene families residing on 1/2/8/20 bearing paralogon (HSA 1/2/8/20), 4 distinct co-duplicated groups were identified with gene families diversified within the time window of vertebrate-invertebrate and tetrapod-bony fish split. First co-duplicated group presented a topology of type ((Hsa20/Hsa2 Hsa1/Hsa13)(Hsa8/ChrX)) and suggests the simultaneous duplication of 2 gene families (Figure 1-A). Second co-duplicated group comprised members from 3 gene families and shows a topology of type (((Hsa1/Hsa6 Hsa8/Hsa6)Hsa20)Hsa1)(Figure 1-B). Third co-duplicated group included 6 gene families and shows a topology of type ((Hsa20 Hsa8/Hsa18)(Hsa1 Hsa8/Hsa6/Hsa2))(Figure 1-C). Fourth co-duplicated group also included 6 gene families and follows a topology of type ((Hsa20 Hsa8/Hsa2) Hsa2/Hsa1/Hsa8)(Figure 1-D).(Pervaiz et al, 2019; Hanif et al, 2012).
Figure 1: Schematic representation of paralogous genes residing in the proposed fourfold paralogy regions on Hsa 1/2/8/20. In each case the percentage bootstrap support is given in parentheses and only values ≥50% are presented here. The connecting bars on the left depict the close physical linkage. * Represents situation where a gene family member is not residing on 1/2/8/20 paralogon.
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