Study of the Molecular Basis of Tame and Aggressive Behavior in the Silver Fox Model
International Collaborative Study between
The James A. Baker Institute for Animal Health, Cornell University, USA,
The Institute of Cytology and Genetics, Russian Academy of Sciences, Russia, and
Department of Biology, University of Utah, USA
Fox Genome
Construction of Meiotic Linkage Map of The Fox Genome
To undertake genetic mapping of behavioral quantitative trait loci (QTLs) in foxes, it is first essential to develop a meiotic-linkage map of the fox genome. Dogs and foxes are markedly different in chromosome number and structure. Although the dog has 78 (mostly acrocentric) chromosomes, the red fox has 34 metacentric chromosomes and from 0 to 8 small B chromosomes. Concordance of the dog and fox karyotypes, as defined by reciprocal chromosomal painting, suggests that the fox karyotype evolved from a more-ancient dog-like karyotype by 26 fusion and 4 fission events (Yang et al., 1999, 2000; Graphodatsky et al., 2000, 2001, 2002). This understanding of the homology among chromosomal segments of the two species lets us predict, to a first approximation, how dog linkage groups should be arranged in the fox genome.
Initially, 700 of the most informative dog microsatellites (Breen et al., 2004) were tested to identify those that robustly amplify fox DNA, and a primary set of 400 microsatellite markers to map the fox genome was developed (Table 2) (Kukekova et al., 2004). Further, 200 polymorphic markers were adapted from canine MSS2 microsatellite set (Clark et al.) and from the 7.6X sequence of canine genome to generate a set of markers which cover the anticipated fox linkage groups completely and uniformly as predicted by comparison of the integrated canine genome map. Complete list of markers will be available upon publication.
Thirty five three-generation fox pedigrees comprising 265 individuals were selected for construction of a meiotic-linkage map of the fox genome. Blood samples were collected at the fox farm in Novosibirsk, Russia, and DNA was extracted for each fox. These pedigrees were genotyped at the Mammalian Genotyping Service of Marshfield Laboratories (Madison, WI) and at Cornell University (280 highly informative markers in total) to construct the meiotic linkage map of the fox genome.
Map construction: Genotyping data was checked for errors using a prepared option of MultiMap (Matise et al., 1994) and used to construct fox linkage groups with a linkage threshold of LOD = 5.0. Chromosomes were individually mapped at LOD = 3.0. Assignment of newly constructed fox linkage groups to chromosomes was based on the established correspondence between dog and fox chromosomes as revealed by cytogenetic studies (Yang et al., 1999; Sargan et al., 2000; Graphodatsky et al., 2002). A meiotic linkage map of VVU1 can be viewed here. A complete map of the fox genome will be available upon publication.
Figure legend. Framework markers (those ordered at LOD score >3.0) have tick marks on chromosome bars. Co-segregating markers with absolute linkage are in the same row or shown as clusters connected to corresponding framework markers. Vertical lines delimit probable intervals for markers mapped with low LOD score. RH map 5000 cR of corresponding dog chromosomes with colored boxes depicting conserved syntenic segments between dog and human are located in the middle part of the figure (adopted from Guyon et al., 2003) Markers commonly mapped onto the fox genetic and the dog RH maps are connected by lines. Idiograms showing the correspondence between each fox chromosome and its dog homologue(s) identified by chromosome painting (adopted from Graphodatsky et al., 2002) are on the right side of each picture. Red stars indicate dog chromosomes for which marker order on the fox meiotic map suggested alternative (flipped) orientation.
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