A linkage map of the ovine X chromosome.

Abstract

A genetic linkage map of the ovine X chromosome containing type I and type II markers has been constructed. The map contains 7 known gene markers and 14 microsatellite markers with a recombination length of 141.9 cM. Segregation of polymorphic markers was observed in a three-generation pedigree containing 480 animals. The maximum number of informative meioses was 912. Additional information was obtained for some markers by following segregation in the AgResearch International Mapping Flock, consisting of nine three-generation full-sib pedigrees. A pseudoautosomal region containing two markers has been identified at one end of the linkage map. Comparisons with mouse and human X chromosomes confirms the observation of Ohno (1973} that the gene content of the mammalian X chromosome is retained. In particular, the conserved grouping of the genes PHKA1, ATP7A, and XIST observed in both the human and the mouse X chromosome appears to be conserved in the sheep X chromosome, and XIST has been mapped to near the center of the chromosome. This study provides the first reported genetic linkage map combining both type I and type 11 markers for any ruminant X chromosome.Until very recently, the X chromosomes of placental mammals were considered to be constrained by Ohno's rule (Ohno 1973), which postulated that genes on the X chromosome of one mammal would be on the X chromosomes of all other mammals. This rule was refined with the discovery that several genes on the short arm of the human X chromosome (Xp) are autosomal in marsupials and monotremes (McKay et al. 1992;Fitzgerald et al. 1993;Graves and Foster 1994). The apparent conservation of gene content of the X chromosomes was thought to be related to the requirement of X-inactivation in females for dosage compensation. The only known exception to this conservation in placental mammals has been a chloride channel gene (CLCN4), which has been shown recently to map to the X chromosome in humans and Mus spretus mice, but to chromosome 7 in C57BL/6 mice (Palmer et al. 1995;Rugarli et al. 1995). The X chromosomes of humans and mice are the most well-characterized and many known X-linked genes and other unique DNA sequences have been mapped in these species (Herman et al. 1994;Willard et al. 1994). Based on mapped gene orders, evolutionary relationships between mice and human X 3Corresponding author. E-MAIL galloways@agresearch.cri.nz; FAX 64-3-477-5413. chromosomes have been explained by five breakpoints and rearrangement of the resulting six blocks of genes (Amar et al. 1988). This concept has been refined recently to accommodate eight conserved segments with seven breakpoints (Blair et al. 1994(Blair et al. , 1995. It is of interest to determine whether the conserved blocks of genes identified in humans and mice remain conserved in other mammalian species, and whether the conservation of these groups has been maintained throughout evolution.The X chromosomes of mammalian species other than human and mouse are less wellcharacterized. In cattle, the genes DMD (Duchenne muscul...

Extensive linkage disequilibrium in a wild bird population

“…As expected, there is considerable difference in male and female recombination rates for the pseudoautosomal region of the Z-chromosome, with the male distance between SJ108 and SJ069 being 41.7 cM as compared to the female distance of 5.1 cM. This increased sexspecific recombination rate between the three pseudoautosomal loci was similar to the observations in the pseudoautosomal regions of the mammalian sex chromosomes, for example in humans [50], ovines [51] and bovines [52]. In the sex-average map, the map density was 4.0 cM/marker among all Z-linked markers and 3.3 cM/marker among the five framework loci.…”

Application of PCR-RFLP technique to determine Booroola gene polymorphism in the Sangsari sheep breed of Iran

“…The fact is that no association was found between those breeds, suggesting that other major gene(s) effects, other than the FecB gene, may be responsible for the high prolificacy of those groups of sheep breeds (1,3,9,25,28,29).…”

An Enhanced Linkage Map of the Sheep Genome Comprising More Than 1000 Loci

“…An additional 17 anonymous loci (\BM1520, \BM6404, \BM7165, \BM7213, \BM8217, \BMC6004, \BMS109, \BMS1120, \BMS1232, \BMS1318, \BMS1932, \BMS345, \BMS66, \BP7, \CSSM041, \INRA049, and \INRA194) have been mapped on the MARC sheep flock (de Gortari et al 1998) but not on the IMF, and an additional 6 markers (ATP7A, DMD, PDHA1, PHKA1, TGLA72 and TGLA89) have been mapped on the sheep X Mapping Flock (XMF; Galloway et al 1996) but not on the IMF. The chromosomal assignments of these markers are also indicated in Figure 1.…”

“…construction of low-density autosomal and X chromosome linkage maps (Crawford et al 1995;Broom et al 1996;Galloway et al 1996;Lord et al 1996;McLaren et al 1997;de Gortari et al 1998). For livestock species, such as sheep and cattle, where the costs of rearing and trait evaluation are high relative to the costs of typing a marker (100-1000 : 1), it has been estimated for quantitative trait loci (QTL) studies and genome scans that the optimum spacing between markers lies between 10 and 30 cM (Darvasi and Soller 1994).…”