ISSUE HIGHLIGHTS

Maximum likelihood estimation of linkage disequilibrium in half-sib families, pp. 195–213

L. Gomez-Raya

The pattern of linkage disequilibrium—the association between alleles at different loci—is central to understanding the evolution of animal and plant genomes and for finding genes affecting production and disease traits. This author proposes novel statistical methods for estimation of linkage disequilibrium in populations with a half-sib structure, such as cattle, sheep, and several species of trees. The methods are tested via Monte Carlo computer simulation and with genotype data from a cattle family.

Temperature-sensitive and circadian oscillators of Neurospora crassa share components, pp. 119–131

Suzanne Hunt, Mark Elvin, and Christian Heintzen

Circadian clocks are molecular timers that organize daily events in cells. There is evidence that cells have many other cellular oscillators, but their components are largely unknown. This article describes a protein complex that is both part of a temperature-induced oscillator called TI-FLO and a component of the circadian clock. This suggests that several cellular oscillators may be linked via common components.

Evaluating the evidence for transmission distortion in human pedigrees, pp. 215–232

Wynn K. Meyer, Barbara Arbeithuber, Carole Ober, Thomas Ebner, Irene Tiemann-Boege, Richard R. Hudson, and Molly Przeworski

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Genome scans for transmission ratio distortion regions in mice, pp. 247–259

Joaquim Casellas, Rodrigo J. Gularte, Charles R. Farber, Luis Varona, Margarete Mehrabian, Eric E. Schadt, Aldon J. Lusis, Alan D. Attie, Brian S. Yandell, and Juan F. Medrano

One way to identify targets of ongoing selection is to look at how often heterozygous parents transmit each of their two different alleles at a locus. These two articles describe genome-wide scans of mice and humans for loci that exhibit transmission ratio distortion (TRD). Candidate loci were identified in both species, but both articles illuminate the statistical challenges in identifying such loci.

Tracing the emergence of a novel sex-determining gene in medaka, Oryzias luzonensis, pp. 163–170

Taijun Myosho, Hiroyuki Otake, Haruo Masuyama, Masaru Matsuda, Yoko Kuroki, Asao Fujiyama, Kiyoshi Naruse, Satoshi Hamaguchi, and Mitsuru Sakaizumi

This article describes a new type of sex-determining gene—Gsdf ^y (gonadal soma derived growth factor on the Y chromosome)—that encodes a growth factor in Oryzias luzonensis, a close relative of medaka fish. It has replaced medaka's sex-determining gene—Dmy—as the master sex-determining gene in this fish. Gsdf is downstream of Dmy in the sex-determining cascade, suggesting that the emergence of a Dmy-independent Gsdf allele led to the appearance of this novel sex-determining gene in O. luzonensis.

Using the Genetics Concept Assessment to document persistent conceptual difficulties in undergraduate genetics courses, pp. 21–32

Michelle K. Smith and Jennifer K. Knight

Why is genetics difficult for undergraduates to learn? What genetics concepts do students typically struggle with? Using student answers to the Genetics Concept Assessment, Smith and Knight identify common student conceptual difficulties and demonstrate that these incorrect ideas frequently persist despite instruction. They describe the likely reasons for such difficulties and identify techniques to help students learn genetics. Educators can use the information in this article to investigate whether their students share the same persistent incorrect ideas.

Haploidization in Saccharomyces cerevisiae induced by a deficiency in homologous recombination, pp. 279–284

Wei Song and Thomas D. Petes

This article describes how diploid cells can give rise to haploid cells without passing through meiosis. The authors show that diploid yeasts that lack Rad52, which is required for efficient homologous recombination, often undergo progressive chromosome loss, eventually becoming haploids. This progressive chromosome loss is likely due to the greatly reduced ability of rad52 strains to repair double-stranded DNA breaks.

Detecting maternal-effect loci by statistical cross-fostering, pp. 261–277

Jason Wolf and James M. Cheverud

Maternal genetic effects are a major component of genetic architecture, but their genetic basis is murky. Studying maternal genetic effects is challenging because mothers and their offspring share half their genes, and consequently their investigation typically requires manipulations (such as cross-fostering) to separate the influences of the maternal and offspring genomes. These investigators develop a framework they call “statistical cross-fostering” to study maternal genetic effects in populations, without using experimental manipulation on those populations. Their approach therefore overcomes one of the major obstacles to studying maternal genetic effects and should pave the way for future investigation of their importance in genetic architecture. Using this framework, the authors identify six maternal-effect loci in mice that would otherwise be missed had traditional analysis of genetic architecture been used.

This Month's Perspectives

James F. Crow: Storied teacher, leader, and colleague at the University of Wisconsin, pp. 1–5

Millard Susman and Rayla Greenberg Temin

In this month's Perspectives article, the authors reminisce about James F. Crow as a colleague at the University of Wisconsin-Madison. They discuss his emergence as a scholar and teacher, his growing friendships in the world of genetics luminaries, and his special approaches to learning, thinking, and sharing knowledge with colleagues and students. The narrative includes some choice stories that help to explain his remarkable influence on science and society.

This Month's Review

Regulation of histone gene expression in budding yeast, pp. 7–20

Peter R. Eriksson, Dwaipayan Ganguli, V. Nagarajavel, and David J. Clark

Histone proteins are abundant in cells, and their levels must be matched to their need. It is not surprising that regulation of histone gene expression is complex, being subject to both positive and negative controls. This review summarizes what is known about the regulation of histone levels and provides novel insight into links between chromatin remodeling proteins and feedback regulation of histone gene expression.

This Month in the American Journal of Human Genetics

Population demographic history can cause the appearance of recombination hotspots, Am. J. Hum. Genet. 90(5)

Henry R. Johnston and David J. Cutler

Recombination hotspots in the human genome could be more apparent than real, according to the authors of this article. Johnston and Cutler show that apparent recombination hotspots could be an artifact of variable effective size of the human population. Their models that assume constant recombination rate but changing effective population size yield LD and variation patterns that are qualitatively and quantitatively similar to those in the human population.