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In the Brassicaceae plant family, which includes the Arabidopsis and Brassica genera, self-incompatibility (SI) is controlled by genes at the S locus. Using experimental crosses, we studied the pattern of inheritance of S-locus alleles in the wild species Brassica cretica. Four full-sib families were established and unequal segregation of alleles at the SRK SI gene was found in one family. The segregation distortion acted in favour of a recessive (class II) allele and was best explained by some form of gametic-level selection. Our findings are discussed in the light of theoretical predictions of differential accumulation of deleterious mutations among S-locus alleles.
Previously we performed a 1012-generation mutation accumulation (MA) study in yeast and found that a surprisingly large proportion of fitness-altering mutations were beneficial. To verify this result and assess the impact of sampling error in our previous study, we have continued the MA experiment for an additional 1050 cell generations and re-estimated mutation parameters. After correcting for biases due to selection, we estimate that 13% of the mutations accumulated during this study are beneficial. We conclude that the high proportions of beneficial mutations observed in this and our previous study cannot be explained by sampling error. We also estimate the genome-wide mutation rate to be 13·7×10−5 mutations per haploid genome per cell generation and the absolute value of the average heterozygous effect of a mutation to be 7·3%.
The hobo-related sequences (hRSs) were considered as degenerate and inactive elements until recently, when one mobilizable copy was described. Using this sequence as the initial seed to search for homologous sequences in 12 available Drosophila genomes, in addition to searching for these sequences by PCR and Southern blot in nine other species, we found homologous sequences in every species of the Drosophila melanogaster species subgroup. Some evidence suggests that these non-autonomous sequences were kept mobilizable for at least 0·4 million years. Also, some very short sequences with miniature inverted-repeat transposable element (MITE) characteristics were found among these hRSs. These hRSs and their ‘MITE-like’ counterparts could provide a good example of the steps proposed in models that describe the MITEs origin.
Mutations in the RNA interference (RNAi) genes aubergine (aub), homeless and piwi were tested for effects on the frequency, distribution and coincidence of meiotic crossovers in the long arm of the X chromosome. Some increases in crossover frequency were seen in these tests, but they may have been due to a maternal effect of the balancer chromosomes that were used to maintain the RNAi mutations in stocks rather than to the RNAi mutations themselves. These same balancers produced strong zygotic interchromosomal effects when tested separately. Mutations in aub and piwi did not affect the frequency of crossing over in the centric heterochromatin of chromosome II; nor did a balancer chromosome III.
Total body fat mass (TBFM) and total body lean mass (TBLM) are the major components of the human body. Although these highly correlated phenotypic traits are frequently used to characterize obesity, the specific shared genetic factors that influence both traits remain largely unknown. Our study was aimed at identifying common quantitative trait loci (QTLs) contributing to both TBFM and TBLM. We performed a whole genome-linkage scan study in a large sample of 3255 subjects from 420 Caucasian pedigrees. Bivariate linkage analysis was carried out in both the entire sample and gender-specific subsamples. Several potentially important genomic regions that may harbour QTLs important for TBFM and TBLM were identified. For example, 20p12-11 achieved a LOD score of 2·04 in the entire sample and, in the male subsample, two genomic regions, 20p12 (LOD=2·08) and 3p26-25 (LOD=1·92), showed suggestive linkage. In addition, two-point linkage analyses for chromosome X showed suggestive linkages on Xp22 in the entire sample (LOD=2·14) and significant linkage on Xp22 in the female subsample (LOD=3·05). Complete pleiotropy was suggested for 20p12 and 3p26-25 in males. Our results suggest that QTLs on chromosomes 20p12, 3p26-25 and Xp22 may jointly influence TBFM and TBLM. Further fine mapping and gene identification studies for these pleiotropic effects are needed.
Twin studies have been used to understand the sources of genetic and environmental variation in body height, body weight and other common human quantitative traits. However, it is rather unclear whether these two sources of variation could be really separated in practice. Here, we consider a special study design where phenotype data from married couples and their siblings have been collected. The marital status gives information about the shared environment, while siblings give information about both genetic and environmental variation. To dissect sources of variation and to allow some deviations and pedigree errors in the data, we model such data using a robust polygenic model with finite genome length assumption. As a summary, we provide the estimates for age-dependent proportions of total variation which are due to polygenic and environmental effects. Here, these estimates are provided for body height, weight, systolic blood pressure and total serum cholesterol measured from subjects of the Indian Migration Study.