Dawson Deborah A, Akesson Mikael, Burke Terry, Pemberton Josephine M, Slate Jon, Hansson Bengt
Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, United Kingdom.
Mol Biol Evol. 2007 Jul;24(7):1537-52. doi: 10.1093/molbev/msm071. Epub 2007 Apr 13.
Genome structure has been found to be highly conserved between distantly related birds and recent data for a limited part of the genome suggest that this is true also for the gene order (synteny) within chromosomes. Here, we confirm that synteny is maintained for large chromosomal regions in chicken and a passerine bird, the great reed warbler Acrocephalus arundinaceus, with few rearrangements, but in contrast show that the recombination-based linkage map distances differ substantially between these species. We assigned a chromosomal location based on sequence similarity to the chicken genome sequence to a set of microsatellite loci mapped in a pedigree of great reed warblers. We detected homologous loci on 14 different chromosomes corresponding to chicken chromosomes Gga1-5, 7-9, 13, 19, 20, 24, 25, and Z. It is known that 2 passerine macrochromosomes correspond to the chicken chromosome Gga1. Homology of 2 different great reed warbler linkage groups (LG13 and LG5) to Gga1 allowed us to locate the split to a position between 20.8 and 84.8 Mb on Gga1. Data from the 5 chromosomal regions (on Gga1, 2, 3, 5, and Z) with 3 or more homologous loci showed that synteny was conserved with the exception of 2 large previously unreported inversions on Gga1/LG5 and Gga2/LG3, respectively. Recombination data from the 9 chromosomal regions in which we identified 2 or more homologous loci (accounting for the inversions) showed that the linkage map distances in great reed warblers were only 6.3% and 13.3% of those in chickens for males and females, respectively. This is likely to reflect the true interspecific difference in recombination rate because our markers were not located in potentially low-recombining regions: several linkage groups covered a substantial part of their corresponding chicken chromosomes and were not restricted to centromeres. We conclude that recombination rates may differ strongly between bird species with highly conserved genome structure and synteny and that the chicken linkage map may not be suitable, in terms of genetic distances, as a model for all bird species.
已发现基因组结构在亲缘关系较远的鸟类之间高度保守，并且基因组有限部分的最新数据表明，染色体内部的基因顺序（同线性）也是如此。在此，我们证实鸡和一种雀形目鸟类大苇莺（Acrocephalus arundinaceus）的大染色体区域保持同线性，重排很少，但相比之下，这些物种基于重组的连锁图谱距离存在显著差异。我们根据与鸡基因组序列的序列相似性，将一组在大苇莺家系中定位的微卫星位点定位于染色体位置。我们在与鸡染色体Gga1 - 5、7 - 9、13、19、20、24、25和Z相对应的14条不同染色体上检测到同源位点。已知2条雀形目大染色体对应于鸡染色体Gga1。2个不同的大苇莺连锁群（LG13和LG5）与Gga1的同源性使我们能够将分裂定位到Gga1上20.8至84.8 Mb之间的位置。来自5个具有3个或更多同源位点的染色体区域（在Gga1、2、3、5和Z上）的数据表明，除了分别在Gga1/LG5和Gga2/LG3上有2个以前未报道的大倒位外，同线性得以保留。我们在其中鉴定出2个或更多同源位点（考虑到倒位）的9个染色体区域的重组数据表明，大苇莺中雄性和雌性的连锁图谱距离分别仅为鸡的6.3%和13.3%。这可能反映了重组率的真实种间差异，因为我们的标记并不位于潜在的低重组区域：几个连锁群覆盖了其相应鸡染色体的很大一部分，并且不限于着丝粒。我们得出结论，在基因组结构和同线性高度保守的鸟类物种之间，重组率可能存在很大差异，并且就遗传距离而言，鸡的连锁图谱可能不适用于作为所有鸟类物种的模型。
