An EST-Enriched Comparative Map of \u3cem\u3eBrassica oleracea\u3c/em\u3e and \u3cem\u3eArabidopsis thaliana\u3c/em\u3e

A detailed comparative map of Brassica oleracea and Arabidopsis thaliana has been established based largely on mapping of Arabidopsis ESTs in two Arabidopsis and four Brassica populations. Based on conservative criteria for inferring synteny, “one to one correspondence” between Brassica and Arabidopsis chromosomes accounted for 57% of comparative loci. Based on 186 corresponding loci detected in B. oleracea and A. thaliana, at least 19 chromosome structural rearrangements differentiate B. oleracea and A. thaliana orthologs. Chromosomal duplication in the B. oleracea genome was strongly suggested by parallel arrangements of duplicated loci on different chromosomes, which accounted for 41% of loci mapped in Brassica. Based on 367 loci mapped, at least 22 chromosomal rearrangements differentiate B. oleracea homologs from one another. Triplication of some Brassica chromatin and duplication of some Arabidopsis chromatin were suggested by data that could not be accounted for by the one-to-one and duplication models, respectively. Twenty-seven probes detected three or more loci in Brassica, which represent 25.3% of the 367 loci mapped in Brassica. Thirty-one probes detected two or more loci in Arabidopsis, which represent 23.7% of the 262 loci mapped in Arabidopsis. Application of an EST-based, cross-species genomic framework to isolation of alleles conferring phenotypes unique to Brassica, as well as the challenges and opportunities in extrapolating genetic information from Arabidopsis to Brassica and to more distantly related crops, are discussed

Molecular dissection of interspecific variation between Gossypium hirsutum and G. barbadense (cotton) by a backcross-self approach : II. Fiber fineness

A backcross-self population from a cross between Gossypium hirsutum and G. barbadense was used to dissect the molecular basis of genetic variation governing two parameters reflecting lint fiber fineness and to compare the precision of these two measurements. By applying a detailed restriction fragment length polymorphism (RFLP) map to 3,662 BC3F2 plants from 24 independently derived BC3 families, we were able to detect 32 and nine quantitative trait loci (QTLs) for fiber fineness and micronaire (MIC), respectively. The discovery of larger numbers of QTLs in this study than previously found in other studies based on F2 populations grown in favorable environments reflects the ability of the backcross-self design to resolve smaller QTL effects. Although the two measurements differed dramatically in the number of QTLs detected, seven of the nine MIC QTLs were also associated with fiber fineness. This supports other data in suggesting that fiber fineness more accurately reflects the underlying physical properties of cotton fibers and, consequently, is a preferable trait for selection. “Negative transgression,” with the majority of BC3F2 families showing average phenotypes that were poorer than that of the inferior parent, suggests that many of the new gene combinations formed by interspecific hybridization are maladaptive and may contribute to the lack of progress in utilizing G. barbadense in conventional breeding programs to improve upland cotton

An EST-enriched Comparative Map of Brassica oleracea and Arabidopsis thaliana

A detailed comparative map of Brassica oleracea and Arabidopsis thaliana has been established based largely on mapping of Arabidopsis ESTs in two Arabidopsis and four Brassica populations. Based on conservative criteria for inferring synteny, “one to one correspondence” between Brassica and Arabidopsis chromosomes accounted for 57% of comparative loci. Based on 186 corresponding loci detected in B. oleracea and A. thaliana, at least 19 chromosome structural rearrangements differentiate B. oleracea and A. thaliana orthologs. Chromosomal duplication in the B. oleracea genome was strongly suggested by parallel arrangements of duplicated loci on different chromosomes, which accounted for 41% of loci mapped in Brassica. Based on 367 loci mapped, at least 22 chromosomal rearrangements differentiate B. oleracea homologs from one another. Triplication of some Brassica chromatin and duplication of some Arabidopsis chromatin were suggested by data that could not be accounted for by the one-to-one and duplication models, respectively. Twenty-seven probes detected three or more loci in Brassica, which represent 25.3% of the 367 loci mapped in Brassica. Thirty-one probes detected two or more loci in Arabidopsis, which represent 23.7% of the 262 loci mapped in Arabidopsis. Application of an EST-based, cross-species genomic framework to isolation of alleles conferring phenotypes unique to Brassica, as well as the challenges and opportunities in extrapolating genetic information from Arabidopsis to Brassica and to more distantly related crops, are discussed

A Genomewide Linkage-Disequilibrium Scan Localizes the Saguenay–Lac-Saint-Jean Cytochrome Oxidase Deficiency to 2p16

Leigh syndrome (LS) affects 1/40,000 newborn infants in the worldwide population and is characterized by the presence of developmental delay and lactic acidosis and by a mean life expectancy variously estimated at 3–5 years. Saguenay–Lac-Saint-Jean (SLSJ) cytochrome oxidase (COX) deficiency (LS French-Canadian type [LSFC] [MIM 220111]), an autosomal recessive form of congenital lactic acidosis, presents with developmental delay and hypotonia. It is an LS variant that is found in a geographically isolated region of Quebec and that occurs in 1/2,178 live births. Patients with LSFC show a phenotype similar to that of patients with LS, but the two groups differ in clinical presentation. We studied DNA samples from 14 patients with LSFC and from their parents, representing a total of 13 families. Because of founder effects in the SLSJ region, considerable linkage disequilibrium (LD) was expected to surround the LSFC mutation. We therefore performed a genomewide screen for LD, using 290 autosomal microsatellite markers. A single marker, D2S1356, located on 2p16, showed significant (P < 10(−5)) genomewide LD. Using high-resolution genetic mapping with additional markers and four additional families with LSFC, we were able to identify a common ancestral haplotype and to limit the critical region to ∼2 cM between D2S119 and D2S2174. COX7AR, a gene encoding a COX7a-related protein, had previously been mapped to this region. We determined the genomic structure and resequenced this gene in patients with LSFC and in controls but found no functional mutations. Although the LSFC gene remains to be elucidated, the present study demonstrates the feasibility of using a genomewide LD strategy to localize the critical region for a rare genetic disease in a founder population

Toward a Unified Genetic Map of Higher Plants, Transcending the Monocot-Dicot Divergence

Closely related (confamilial) genera often retain large chromosomal tracts in which gene order is colinear, punctuated by structural mutations such as inversions and translocations 1. To explore the possibility that conservation of gene order might extrapolate to more distantly related taxa, we first estimated an average structural mutation rate. Nine pairs of taxa, for which there exist both comparative genetic maps and plausible estimates of divergence time, showed an average of0.14 (±0.06) structural mutations per chromosome per million years of divergence (Myr; Table 1). This value is offered as a first approximation, acknowledging that refined comparative data and/or divergence estimates may impel revision.This letter is from Nature Genetics 14 (1996): 380, doi:10.1038/ng1296-380.</p