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3:49 video, Alzheimer's disease is the most common cause of dementia, affecting over 40 million people worldwide. And though it was discovered over a century ago, scientists are still grappling for a cure. Ivan Seah Yu Jun describes how Alzheimer's affects the brain, shedding light on the different stages of this complicated, destructive disease.

Vibrio harveyi is a marine bacteria that emits light only at high population density. The bacterial bioluminescence is controlled by a system called quorum sensing. In this system, signaling molecules are secreted, and when they bind to cell surface receptors, they turn on many genes, including those that produce bioluminescence.

The Hawaiian Bobtail squid has a remarkable symbiotic relationship with a species of marine bacteria that can produce light by a controlled chemical reaction. Also featured on the HHMI DVD, Exploring Biodiversity: The Search for New Medicines, available free from HHMI.

Questions about the nature of viruses remain quite vexing. Recent studies of the giant Mimivirus illustrate this point. Its large size and correspondingly large genome test our general ideas of viruses as small, simple entities. The existence of genes associated with translation, metabolism, DNA repair, and protein folding raises questions about the evolutionary history of viruses. Further studies of this virus, and the search for other giant viruses, may shed light on these issues.

To keep your kids from developing an allergy to peanuts, should you give them nuts at an early age or withhold them? For years the debate has generated more heat than light, but today a landmark study led by King's College London researchers offers some potent evidence that suggests giving peanuts to infants dramatically decreases the risk of developing an allergy to peanuts.

Comparing features of a 4.4-million-year-old fossil skeleton to those of human and chimpanzee skeletons sheds light on our evolutionary history.

15. That's all you need to know about the measles. OK, that's not true at all. There's no one weird trick that will give you a flat belly (besides lying face-down on something flat), and there's no one weird number that explains measles epidemiology. But the basic reproduction number, or R0, of a disease does shed some light on which diseases become epidemics and how we can keep them in check.

Life on Earth is intimately connected to the natural cycles of light and dark that make up a 24-hour day. For plants, animals, and even bacteria, these circadian rhythms control many biological functions. Humans can overrule their body clocks, but at a price: People whose circadian rhythms are regularly disrupted-by frequent jet lag or shift work, for example-are more vulnerable to diabetes, obesity, cardiovascular disease, and cancer. There are various theories to explain these associations, and researchers now have a new player to consider: the bacteria that live in the digestive tract. According to a study in mice and a small group of human volunteers, the internal clocks of these gut microbes sync up with the clocks of their hosts. When our circadian rhythms get out of whack, so do those of our bacteria.

These case studies heralded a new appreciation for the phenomenon of genetic chimerism-when an individual carries two or more genetically distinct cell lines in different parts of her body. Until the advent of techniques for blood typing and karyotyping cells, genetic chimeras where thought to be very rare. They only came to light when the phenotypes associated with the two distinct genomes were so discordant that the resulting individual was clearly exceptional, with patches of distinct skin coloration throughout the body, for example, or hermaphroditic genitals. In reality, genetic chimeras may be quite common, disguised in perfectly normal bodies harboring genetically distinct cell lineages.

Dr. Carolyn Henry, a veterinary oncologist at the University of Missouri veterinary school, says that, unlike lab mice, dogs get cancer naturally, just like humans. So their cancers are more likely to behave like human cancer when treated. "It's the same disease, it really doesn't matter what the species is," Henry says. "It's the same disease if it occurs naturally. And so, answers in one species should translate to answers in other species in many cases."

Links to teacher's guide for October articles Eating with your eyes: The Chemistry of Food Colorings Tooth Decay: A Delicate Balance Probiotics: Good bactria good health Dirt? Who needs it? How hydroponics is poised to change the world Light in the cellar of the sea

Now, scientists at the Salk Institute for Biological Studies in La Jolla, Calif., have pinpointed a gene linked to these disorders that seems to be crucial for normal brain structure in prenatal development. The findings, which appear in an open-access article in the Jan. 14 issue of Cell Reports, shed new light on the mechanistic workings of a gene called MDGA1, previously implicated in autism, schizophrenia and bipolar disorder.

A decade-old technique that allows researchers to control brain function in lab animals could partially restore sight to the blind. In a trial sponsored by RetroSense Therapeutics, a startup company in Ann Arbor, Michigan, doctors will inject a harmless virus loaded with DNA from photoreceptive algae into the eyes of 15 patients suffering from retinitis pigmentosa. The experimental procedure represents the first human test of optogenetics, which is a technique that genetically modifies neurons to make them responsive to light. Doctors from the Retina Foundation of the Southwest will perform the procedure, and attempt to transfer the job duties of photoreceptor cells to different cells in the eye to restore sight.

One concern repeatedly raised by critics who don't want the FDA to give the transgenic fish the green light: What would happen if these fish got out of the land-based facilities where they're grown and escaped into the wild? Would genetically modified salmon push out their wild counterparts or permanently alter habitat? In a review paper published this month in the journal BioScience, scientists tackle that very question. Robert H. Devlin, a scientist at Fisheries and Oceans Canada, led a team that reviewed more than 80 studies analyzing growth, behavior and other trait differences between genetically modified and unaltered fish. The scientists used this to predict what might happen if fish with modified traits were unleashed in nature.

Would you rather be bitten by a venomous rattlesnake or touch a poisonous dart frog? While both of these animals are capable of doing some serious damage to the human body, they deliver their dangerous toxins in different ways. Rose Eveleth sheds light on the distinction between poison and venom (and why you shouldn't treat either one like you've seen in the movies).

Was the "Brooklyn Butcher" of 1926 a cold-blooded killer or was something less sinister at play? This interrupted case study introduces students to hemoglobin binding and carbon monoxide poisoning by working through the details of a fictionalized account of a true-crime story. Topics covered include molecule conformational states, binding affinity, deoxyhemoglobin, oxyhemoglobin, carboxyhemoglobin, and oxygen transport. Students also design an experiment to determine the cause of death of the victim. Prior to beginning the activity students should have some knowledge of the respiratory and circulatory systems and be familiar with oxygen binding curves. Detailed understanding of hemoglobin conformational changes is not necessary since this information is covered in the case. Students will also learn briefly about the electromagnetic spectrum and visible light. Originally developed for a non-majors, pre-nursing anatomy and physiology course, the case is also appropriate for use in any of the following courses: introductory biochemistry, introductory biology, introductory chemistry, nursing, exercise physiology, or possibly even introductory physics.

In this interrupted case study developed for use in a flipped classroom, students read about a picnic that takes place in autumn during the peak of fall color and along the way learn about light absorption by photosynthetic pigments, why leaves turn color in the fall, atmospheric CO2 concentrations and their effect on photosynthesis, and the C3, C4, and CAM photosynthetic pathways. The case is designed to provide introductory biology students with a basic understanding of photosynthetic pathways and how environmental factors affect plants using these pathways. The activity could also be used in an advanced high school biology course covering photosynthesis. The case includes several short videos that students watch as homework before coming to class so that they are prepared to work together in class in small groups to answer the case questions.

Weaving Social Justice Into Science Instruction Shedding light on inequity in science fields bolsters students' critical thinking skills and sense of self-efficacy in science. A free curriculum helps teachers get started.

We know poisonous snakes are dangerous, but what exactly makes venom so powerful? Evolutionary biology tells us why venom is useful for snakes, but chemistry tells us how venom works. This week, Reactions sheds some light on the proteins in venom, as well as its potential medical uses

Great video footage

The laboratory-based animal study found a link between greater susceptibility to obesity and diabetes, and whether one's ancestors have been undernourished for several generations, and was published on Friday in the journal Cell Metabolism.