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Men shed more bacteria into their surroundings than women do, studies have shown. Now scientists have found that men and women have different effects on the variety of bacteria inside a home, too. The variation comes down to skin biology and "perhaps to body size and hygiene practices," note researchers who sequenced the genes in dust that had settled on the tops of doors in 1,200 homes across the U.S. Dogs apparently alter indoor bacteria more extensively than humans or cats. The bacterial signatures of each of these living beings are unique enough that by simply testing dust in a home, investigators can accurately predict if more women or men live there and if dogs or cats do as well.

Quintana-Murci and his colleagues also took advantage of a previously published map of areas of the human genome where Neanderthal genes are present, showing that innate immune genes are generally more likely to have been borrowed from Neanderthals than genes coding other types of proteins. Specifically, they noted that 126 innate immune genes in present-day Europeans, Asians, or both groups were among the top 5 percent of genes in the genome of each population most likely to have originated in Neanderthals. The cluster of toll-like receptor genes, encoding TLR 1, TLR 6, and TLR 10, both showed signs of having been borrowed from Neanderthals and having picked up adaptive mutations at various points in history. Meanwhile, a group led by Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, used both the same previously published Neanderthal introgression map that Quintana-Murci used and a second introgression map. The researchers searched for borrowed regions of the genome that were especially long and common in present-day humans, eventually zeroing in TLR6, TLR10, and TLR1. These receptors, which detect conserved microbial proteins such as flagellin, are all encoded along the same segment of DNA on chromosome four.

The PBL Clearinghouse contains problems from a wide variety of disciplines. As the problems and supporting materials are covered by the Creative Commons Attribution-NonCommercial 4.0 International License, you are welcome to borrow and adapt these problems for your classroom. Because these files are open sourced, your students may search and discover the teaching notes and solutions. We encourage you to make changes, adapt the problems to your specific goals and classroom contexts and thereby discourage your students from "borrowing" solutions or otherwise circumventing your instructional goals.

This flipped clicker case study explores the fascinating relationship between the Arizona Bark Scorpion (the most venomous scorpion in North America) and the Southern Grasshopper Mouse. Initially it would seem that the grasshopper mouse is no match for the scorpion's venom; however, the grasshopper mouse is easily able to eat the scorpion and is largely immune to the scorpion's sting. By working through this case study, students learn about neuron anatomy and physiology as they explore how the grasshopper mouse is able to survive the scorpion's venom. This case study was developed for an introductory biology course for majors, but it could also be used in an introductory biology course for non-majors or in an anatomy and physiology course. The case requires that students learn basic neuron anatomy and action potential physiology prior to class by reading their textbook or by watching videos on the subjects. An optional set of guided questions tailored to Campbell Biology (10th ed.) is included in the teaching notes.

This case study follows two beginning undergraduate researchers on a quest for a summer research project related to food web ecology. While writing their research proposal, the students receive feedback indicating that they have neglected an entire group of organisms from their food web-parasites, which leads them to a scientific research paper discussing how these organisms have been overlooked by scientists studying food webs, the challenges involved with including parasites in food webs, and the contributions parasites ultimately make to food webs. An integrated activity in which students visualize the food web using images of organisms and answer questions about species interactions provides opportunities to examine key concepts such as omnivory, ontogenetic diet changes, trophic levels, complex life cycles, and taxonomic aggregation. This case study was originally written for an undergraduate general ecology course, but could easily be adapted to undergraduate general biology courses covering community ecology or specific courses in invertebrate zoology, parasitology, or disease ecology. The teaching notes also discuss how the included code for R statistical computing software can be used to extend the case study in a more quantitative direction if desired.

"Reading and understanding scientific literature can be a daunting task for students in introductory science courses. This decision/dilemma case study helps ease them into the process by using a short scientific article with a simple experimental design that compares two types of ACL (anterior cruciate ligament) surgery, autograft and allograft. The case tells the story of Todd, a martial artist who recently tore his ACL in competition. With the help of the article, Todd discusses the potential surgical options provided by his doctor with his friend, Sam, a medical student. The case has the added value of demonstrating how one can use scientific literature to make informed healthcare decisions based on clinical evidence. Please note that the required article (Kane et al., Knee Surgery, Sports Traumatology, Arthroscopy 24(11): 3627-33) is not provided with this case; prior to assigning this material, instructors should confirm that students can access the article, since access may vary by institution."

This case study teaches students about allopatric speciation through an investigation of the benthic and limnetic sticklebacks of Paxton Lake, which are among the youngest species on Earth, diverging from each other after the Pleistocene glaciers melted and the Gulf Islands formed. Researchers at the University of British Columbia have carried out a variety of fascinating studies on these hardy little fish. Results from this research (formatted as data sheets included in the teaching notes) are provided to students who design experiments and then compare actual data to investigate why benthic and limnetic sticklebacks seldom interbreed in Paxton Lake. Developed for a first-year biology course for majors organized around the general theme of evolution and the history of life on Earth, this case study is an updated version of another case in the collection, "Something's Fishy in Paxton Lake" (Sharp, 2001). The current version is especially suited for a flipped classroom in which students prepare for class ahead of time with a reading assignment that also involves the viewing of a video by the case authors that introduces the mechanisms of allopatric speciation.

In this interrupted case study, students meet a pair of fictional newlyweds on their way to Australia for their honeymoon. Initially eager to enjoy the sun, sand, and sights, Tanya and Julien Brahim end up more intimately acquainted with the local wildlife than they had planned. Tanya is bitten by a venomous arachnid and Julien has a run-in with a dangerous cnidarian. This case study was created to help students solidify their knowledge about cardiac myocytes, particularly ion movements associated with action potential generation in autorhythmic and contractile cells. As students work through the case, they will complete fill-in-the-blank paragraphs describing the heart, diagram membrane potentials and ion movements, and compare and contrast action potentials from different cell types. Written for a course in human physiology, the case requires some prior knowledge of membrane potentials, equilibrium potentials, ion gradients, neuronal action potentials, and skeletal muscle action potentials. An optional pre-case assignment (included in the teaching notes) can be used to make sure that students are familiar with the necessary concepts.

This case study presents the mock trial of "Martin Miller." There is no question that Martin killed his girlfriend; he admitted to stabbing her in a violent rage. But what is the degree of his responsibility? By virtue of Martin having the MAOA-L gene variant, together with a history of childhood abuse, should his punishment be reduced? This hypothetical case, which requires students to think through the issues rather than simply look up a verdict, is based on actual events and violent behaviors that resulted in criminal charges claimed to be related to MAOA. The MAOA gene and its effect on behavior have been extensively studied, and research results have been introduced as evidence in court cases with differing results. The present case study allows students to explore how behavioral genetic information can be applied to a courtroom situation, and requires them to integrate information from biology, ethics, and the law. Note: Due to the unusual structure of the case, no answer key is available.

This directed case study was developed in order to present genomic data to students, allow them to interpret the impact of genetic variations on phenotype, and to explore precision medicine. Students are introduced to "Josie," a college sophomore who decides to have her genome sequenced after learning about genome-wide association studies (GWAS) in class. As students work  through the case, they learn about the different technologies that can be used in GWAS studies and interpret Josie's results for a subset of genetic markers that affect a range of traits from pharmacogenetics to disease risk alleles and non-pathogenic traits. Students are confronted with ethical issues such as duty to inform, actionable results, and variants of unknown significance (VUS). Students are also asked to reflect on their feelings about getting genomic testing for themselves. An optional activity for advanced students (included in the teaching notes) involves using the Gene database at NCBI to explore variants of the CYP2C9 gene. The case study is appropriate for use in undergraduate genetics or molecular biology classrooms.

In this activity, students learn why evolution is at the heart of a world health threat. They will investigate the increasing problem of antibiotic resistance in such menacing diseases as tuberculosis and influenza. Students take on the role of staff at a public health agency who are trying to communicate the widespread problem of evolving disease-causing agents to the public.