Genetics, Vol. 174, November 2006, Copyright © 2006

Issue Highlights

The Drosophila fragile X protein, dFMR1, is required during early embryogenesis for pole cell formation and the rapid nuclear division cycles, pp. 1287–1298

Girish Deshpande, Gretchen Calhoun and Paul Schedl

Inactivation of the X-linked FMR gene, one of three related genes encoding KH domain RNA-binding proteins, is the most common cause of mental retardation in humans. The observed phenotypes of FMR mutations point to both a role of this protein in RNA interference (RNAi) and direct involvement in cytoskeletal complexes. This article explores the functions of the single homolog (FMR1) during Drosophila embryogenesis. The parallels with Argonaute-2 (Ago-2) phenotypes provide further support for a regulatory role of FMR1 in the RNAi pathway and also indicate that it is required, like Ago2, to maintain a silenced heterochromatin state.

A deletion at the mouse Xist gene exposes trans-effects that alter the heterochromatin of the inactive X chromosome and the replication time and DNA stability of both X chromosomes, pp. 1115–1133

Silvia V. Diaz-Perez, David O. Ferguson, Chen Wang, Gyorgyi Csankovszki, Chengming Wang, Shih-Chang Tsai, Devkanya Dutta, Vanessa Perez, SunMin Kim, C. Daniel Eller, Jennifer Salstrom, Yan Ouyang, Michael A. Teitell, Bernhard Kaltenboeck, Andrew Chess, Sui Huang and York Marahrens

A deletion of 21 kb from both Xist alleles in female mouse fibroblasts causes the appearance of two histone modifications throughout the inactive X chromosome, both of which are usually associated with euchromatin. Despite these euchromatic properties, the inactive X chromosome replicates even later in S phase than in wild-type female cells. These Xist mutations also destabilized both X chromosomes, leading to deletions and translocations. The deletions also induced the accumulation of {gamma}-H2AX, a histone involved in DNA repair, on the X chromosomes. Thus the Xist locus plays a critical role in maintaining X chromosome stability.

Pronounced differences of recombination activity at the sex determination locus of the honeybee, a locus under strong balancing selection, pp. 1469–1480

Martin Hasselmann and Martin Beye

The sex determination locus (SDL) of the honeybee Apis mellifera is under a well-known mode of strong balancing selection, where homozygous individuals at SDL are eliminated. Nucleotide diversity is inflated sevenfold within the sex determination gene complementary sex determiner (csd) and rapidly declines within 45 kb to genomewide average levels. Although no recombination was observed within SDL, which contains csd, analyses of heterogeneity, shared polymorphic sites, and linkage disequilibrium show that recombination has contributed to the evolution of csd. The local control of recombination appears to be related to SDL's function and mode of selection.

Can random mutation mimic design?: A guided inquiry laboratory for undergraduate students, pp. 1073–1079

Steven T. Kalinowski, Mark L. Taper and Anneke M. Metz

Complex biological structures, such as the human eye, have been interpreted by various members of the lay community as evidence for some form of intelligent design. The authors present an inquiry-based laboratory that explains just how evolution can create such complex structures by using paper airplanes as a model organism. The main task for students in this investigation is to figure out how to simulate paper airplane evolution (including reproduction, inheritance, mutation, and selection). The result is a clever and novel method using paper airplanes to teach students to develop evolutionary models and appreciate the relevance of their models to the origin of complex adaptations.

Estimating recombination rates from single- nucleotide polymorphisms using summary statistics, pp. 1517–1528

Badri Padhukasahasram, Jeffrey D. Wall, Paul Marjoram and Magnus Nordborg

Knowledge of how recombination rates vary across the human genome is of critical importance in disease association mapping and evolutionary inference studies, and is also of interest from the point of view of basic molecular biology. This article describes a novel method for estimating the population recombination parameters from single-nucleotide polymorphisms (SNPs). In this method, the SNP data set is described by multiple summary statistics and then recombination rates are estimated by performing maximum-likelihood inference on the reduced data. The method is first demonstrated on simulated data sets and then used to analyze a large human genotype data set sequenced by Perlegen Sciences.

Dynamic genetic interactions determine odor-guided behavior in Drosophila melanogaster, pp. 1349–1363

Deepa Sambandan, Akihiko Yamamoto, Juan-José Fanara, Trudy F. C. Mackay and Robert R. H. Anholt

Understanding the genetic architecture of complex traits requires identification of the underlying genes and characterization of gene-by-gene and genotype-by-environment interactions. This article describes the results of a large screen for mutations affecting behavior in response to a particular odor in Drosophila melanogaster. Behaviors that mediate interactions between organisms and their environment are complex traits expected to be especially sensitive to environmental conditions. Tests of epistasis among 10 of the mutant strains reveal a remarkable level of environmental context dependence.

Association mapping of complex trait loci with context-dependent effects and unknown context variable, pp. 1597–1611

Mikko J. Sillanpää and Madhuchhanda Bhattacharjee

A novel method for Bayesian analysis of genetic heterogeneity and multilocus association in random population samples is presented. In the method, individuals are stochastically assigned into two etiological groups, each of which can have their own, and possibly different, subsets of trait-associated (disease-predisposing) loci or alleles. The method is favorable in the presence of genetic heterogeneity in the trait or in the presence of unknown genes–environment or genes–gene interactions. Unlike other approaches of handling heterogeneity, which stratify on factors that are known prior to the analysis, the method presented here can cope with heterogeneity due to unobserved covariates, such as unobserved subpopulations.

dSno facilitates Baboon signaling in the Drosophila brain by switching the affinity of Medea away from Mad and toward dSmad2, pp. 1299–1313

Norma T. Takaesu, Cathy Hyman-Walsh, Ying Ye, Robert G. Wisotzkey, Michael J. Stinchfield, Michael B. O'Connor, David Wotton and Stuart J. Newfeld

The authors present genetic and biochemical evidence that a homolog of the Sno oncogene (dSno) mediates signaling via Baboon (activin type I receptor) in Drosophila, possibly by shifting Medea from the Dpp pathway to the activin pathway. This "switch" may help control the balance of proliferation and differentiation in response to TGFβ signaling.


Related articles in Genetics:

Can Random Mutation Mimic Design?: A Guided Inquiry Laboratory for Undergraduate Students
Steven T. Kalinowski, Mark L. Taper, and Anneke M. Metz
Genetics 2006 174: 1073-1079. [Abstract] [Full Text]  

A Deletion at the Mouse Xist Gene Exposes Trans-effects That Alter the Heterochromatin of the Inactive X Chromosome and the Replication Time and DNA Stability of Both X Chromosomes
Silvia V. Diaz-Perez, David O. Ferguson, Chen Wang, Gyorgyi Csankovszki, Chengming Wang, Shih-Chang Tsai, Devkanya Dutta, Vanessa Perez, SunMin Kim, C. Daniel Eller, Jennifer Salstrom, Yan Ouyang, Michael A. Teitell, Bernhard Kaltenboeck, Andrew Chess, Sui Huang, and York Marahrens
Genetics 2006 174: 1115-1133. [Abstract] [Full Text]  

The Drosophila Fragile X Protein dFMR1 Is Required During Early Embryogenesis for Pole Cell Formation and Rapid Nuclear Division Cycles
Girish Deshpande, Gretchen Calhoun, and Paul Schedl
Genetics 2006 174: 1287-1298. [Abstract] [Full Text]  

dSno Facilitates Baboon Signaling in the Drosophila Brain by Switching the Affinity of Medea Away From Mad and Toward dSmad2
Norma T. Takaesu, Cathy Hyman-Walsh, Ying Ye, Robert G. Wisotzkey, Michael J. Stinchfield, Michael B. O'Connor, David Wotton, and Stuart J. Newfeld
Genetics 2006 174: 1299-1313. [Abstract] [Full Text]  

Dynamic Genetic Interactions Determine Odor-Guided Behavior in Drosophila melanogaster
Deepa Sambandan, Akihiko Yamamoto, Juan-José Fanara, Trudy F. C. Mackay, and Robert R. H. Anholt
Genetics 2006 174: 1349-1363. [Abstract] [Full Text]  

Pronounced Differences of Recombination Activity at the Sex Determination Locus of the Honeybee, a Locus Under Strong Balancing Selection
Martin Hasselmann and Martin Beye
Genetics 2006 174: 1469-1480. [Abstract] [Full Text]  

Estimating Recombination Rates From Single-Nucleotide Polymorphisms Using Summary Statistics
Badri Padhukasahasram, Jeffrey D. Wall, Paul Marjoram, and Magnus Nordborg
Genetics 2006 174: 1517-1528. [Abstract] [Full Text]  

Association Mapping of Complex Trait Loci With Context-Dependent Effects and Unknown Context Variable
Mikko J. Sillanpää and Madhuchhanda Bhattacharjee
Genetics 2006 174: 1597-1611. [Abstract] [Full Text]