Population genetic studies of retinitis pigmentosa.

A questionnaire survey characterized a sample of 670 probands with retinitis pigmentosa (RP) and allied disorders. Segregation analysis provided some evidence for a small proportion of sporadic cases and for decreased segregation ratios of the dominant and recessive genotypes, which could be attributed to delayed age of onset in some cases. The overall incidence of RP was indirectly calculated to be approximately 1 in 3,700, while the incidence of autosomal recessive RP, including at least two genocopies, was estimated to be about 1 in 4,450. Family data analysis included the calculation of the likelihood that each family represented autosomal recessive, autosomal dominant, and X-linked inheritance patterns. These likelihoods were then converted to relative probabilities and summed over the sample population to yield estimates of the proportions of the three Mendelian types. This large, heterogeneous sample indicated that approximately 84% of the cases in the United States may be autosomal recessive, while about 10% are dominant and 6% X-linked recessive.     

Etiologic heterogeneity in the familial aggregation of congenital cardiovascular malformations.

Recent data indicate that there is increased risk of congenital cardiovascular malformations (CCVM) within families of probands diagnosed with congenital cardiovascular malformations that are due to altered embryonic blood flow (flow lesions). In the present study, regressive models recently developed by Bonney were used to compare specific models of inheritance and to test for etiologic heterogeneity among three subgroups of 375 flow-lesion families identified by the Baltimore-Washington Infant Study. When all families were analyzed as a single group, the best-fitting model was a simple recessive model with Mendelian transmission; race did not have a significant effect on estimated risk. Separate analyses of families of probands with left heart defects, right heart defects, and ventricular septal defects (VSD) confirmed this simple Mendelian recessive model as the model of choice. However, when race was included as a covariate in these genetic models, there was evidence for significant heterogeneity among the three subgroups. There was an increased risk to relatives of white probands with right heart defects and to relatives of black probands with VSD, while there was no effect of race among relatives of probands with left heart defects. These results strongly suggest that there is etiologic heterogeneity in the control of CCVM among flow-lesion families and that the patterns of familial aggregation differ among the races.     

Restriction-map variation with the yellow-achaete-scute region in five populations of Drosophila melanogaster

It has been proposed that the degree of recombination for a genomic region will affect the level of both nucleotide heterozygosity and the density of transposable elements. Both features of genomic diversity have been examined in a number of recent reports for regions undergoing relatively normal levels of recombination in Drosophila melanogaster. In this study the genomic variation associated with yellow-achaete- scute loci located at the tip of the X chromosome is examined by six- cutter restriction mapping. In this region, as usual for regions adjacent to telomeres, crossing-over is dramatically reduced, and published studies of visible mutants indicate extremely little restriction-map variation. Eight six-cutter restriction endonucleases were used to locate sequence variation in 14- and 16.5-kb regions in 109 lines sampled from North America, Africa, and Europe. The overall level of heterozygosity is estimated as 0.29%. Nine large insertions, all presumed to be transposable elements, were observed. Base-pair heterozygosity appears to be reduced compared with regions having normal levels of recombination. The estimated heterozygosity is much higher than reported in earlier studies of restriction-map variation among visible mutations in the complex. The incidence of large insertions is not elevated compared with that in other regions of the genome. This suggests that asymmetric synapsis and exchange is not an important mechanism for the elimination of transposable elements.      

Essay contest reveals misconceptions of high school students in genetics content

National educational organizations have called upon scientists to become involved in K-12 education reform. From sporadic interaction with students to more sustained partnerships with teachers, the engagement of scientists takes many forms. In this case, scientists from the American Society of Human Genetics (ASHG), the Genetics Society of America (GSA), and the National Society of Genetic Counselors (NSGC) have partnered to organize an essay contest for high school students as part of the activities surrounding National DNA Day. We describe a systematic analysis of 500 of 2443 total essays submitted in response to this contest over 2 years. Our analysis reveals the nature of student misconceptions in genetics, the possible sources of these misconceptions, and potential ways to galvanize genetics education.     

How sensory drive can promote speciation

Some of the most spectacular and diverse traits in animals are the signals used to attract mates. Closely related species often differ dramatically in signaling traits, in spite of similarity in other morphological traits. The idea that reproductive isolation arises when male mating signals and female preferences differ among populations is an old one. However, until recently, there was almost no information on what generates diversity in mating signals and preferences. This is beginning to change, with emerging results that highlight the importance of habitat differences in generating this diversity. Such differences in ecology are at the root of one hypothesis for divergence in sexual signaling – sensory drive. The sensory drive hypothesis focuses on how communication systems adapt to local environments and predicts that divergence in communication systems will occur when environments differ. Reproductive isolation can arise as a byproduct of this adaptive divergence in behavior.     

Synergistic selection between ecological niche and mate preference primes diversification

The ecological niche and mate preferences have independently been shown to be important for the process of speciation. Here, we articulate a novel mechanism by which ecological niche use and mate preference can be linked to promote speciation. The degree to which individual niches are narrow and clustered affects the strength of divergent natural selection and population splitting. Similarly, the degree to which individual mate preferences are narrow and clustered affects the strength of divergent sexual selection and assortative mating between diverging forms. This novel perspective is inspired by the literature on ecological niches; it also explores mate preferences and how they may contribute to speciation. Unlike much comparative work, we do not search for evolutionary patterns using proxies for adaptation and sexual selection, but rather we elucidate how ideas from niche theory relate to mate preference, and how this relationship can foster speciation. Recognizing that individual and population niches are conceptually and ecologically linked to individual and population mate preference functions will significantly increase our understanding of rapid evolutionary diversification in nature. It has potential to help solve the difficult challenge of testing the role of sexual selection in the speciation process. We also identify ecological factors that are likely to affect individual niche and individual mate preference in synergistic ways and as a consequence to promote speciation. The ecological niche an individual occupies can directly affect its mate preference. Clusters of individuals with narrow, differentiated niches are likely to have narrow, differentiated mate preference functions. Our approach integrates ecological and sexual selection research to further our understanding of diversification processes. Such integration may be necessary for progress because these processes seem inextricably linked in the natural world.     

A population-based study of coarctation of the aorta: comparisons of infants with and without associated ventricular septal defect.

BACKGROUND: Coarctation of the aorta (CoA) is a congenital cardiovascular malformation (CCVM) sometimes associated with ventricular septal defect (VSD). Although the phenotypic association is well documented, little research exists on the epidemiological features distinguishing CoA with and without VSD. METHODS: The Baltimore-Washington Infant Study (1981-1989), a population-based study of CCVM, evaluated 126 infants with "pure" CoA (free of associated cardiac defects) and 67 infants with CoA and VSD (COA/VSD) in comparison to 3,572 controls. RESULTS: The proportion of infants with associated extracardiac anomalies was greater among CoA/VSD than among pure CoA (31% versus 11%). Infants with CoA/VSD were twice as likely as those with pure CoA to be born small for gestational age (23% versus 12%, respectively, compared with 6% of controls). All-cause mortality during the first year of life was higher in CoA/VSD than in pure CoA (21% vs. 7%). Multiple logistic regression models revealed that family history of CCVM was associated with pure CoA (adjusted case-control odds ratio [OR] = 4.6; 99% confidence interval [CI] = 1.5-13.9) and with CoA/VSD (OR = 5.9, CI = 1.2-23.5); maternal history of organic solvent exposures early in pregnancy was also associated with pure CoA (OR = 3.2, CI = 1.0-10.2) and with CoA/VSD (OR = 3.7, CI 0.9-14.9). Additional risk factors, including maternal epilepsy (OR = 5.3, CI = 0.9-30.6), and use of macrodantin (OR = 6.7, CI = 1.4-31.8) were associated only with pure CoA. CONCLUSIONS: These findings highlight possible genetic and environmental differences between pure CoA and CoA/VSD and may stimulate further investigations of the etiology of CoA.     

Characterisation of<Emphasis Type="Italic">fusarium graminearum</Emphasis> and<Emphasis Type="Italic">F. culmorum</Emphasis> isolates by mycotoxin production and aggressiveness to wheat

A total of 27Fusarium culmorum isolates from Germany and 41F. graminearum isolates from Kenya were investigated for aggressiveness and mycotoxin production on wheat ears. In addition, ergosterol content of the kernels from ears inoculated withF. graminearum was determined and theF. culmorum isolates were tested for mycotoxin productionin vitro. For both pathogens, isolates markedly differed in aggressiveness. 59% and 37% of theF. culmorum isolates produced NIV and DON, respectively,in vivo andin vitro. The DON-producing isolates also produced 3-acDONin vitro. The more aggressive isolates produced mainly DON while the less aggressive isolates produced mainly NIV. 12% and 85% of theF. graminearum isolates produced NIV and DON, respectively. The highly aggressive isolates produced higher amounts of DON, aggressiveness being highly correlated to DON content in the kernels. NIV-producing isolates were less aggressive. Ergosterol content of kernels was moderately correlated to aggressiveness but highly correlated to DON content. Disease severity was associated with kernel weight reduction.