As a dog breeder, it is easier to select for a recessive trait, because when a dog has that trait, one can infer its genetic makeup. When a dog has a dominant trait, it could carry two dominant genes for the trait, or the dominant gene and a recessive gene. In the latter case, descendents may crop up that have inherited two copies of the recessive gene. Deducing which ancestors were carrying that recessive gene, and eliminating the gene from the gene pool, may take many generations of crosses.

In practice, genetics is even more complicated. Usually more than two possible genes for a trait exist. Also, the activity of genes can be modified by other genes. For example, multiple genes interact to specify the color and shade of a dog's coat.

It took more than a quarter century for Boston terriers, black Russian terriers, and golden retrievers, breeds developed since the 1850s (recent enough for a somewhat reliable historical account), to breed true.

The process can be speeded up by increasing inbreeding, because breeding related dogs decreases the amount of variation in the gene pool. However, too much inbreeding can introduce genetic defects, such as decreased immunity and increased risk of cancer.

The Labradoodle originated in Australia in the 1970s or 1980s (accounts differ) as an attempt to produce a low-allergy guide dog for the blind. Labradoodles are not recognized as a breed by the American Kennel Club or other well-respected registries. The Labradoodle breed standard is currently too broad. For example, three categories of coat textures are recognized, ranging from a relatively flat Labrador-like coat to a curly poodle-type coat.

Taking to the sky I read that the Wright brothers, who flew the first airplane, built their own engine, although at the time n.o.body knew how to build one and fire it up. There were no tools to make the hole for the piston, and so forth. Can you shed some light on this?

Charles Taylor, a talented machinist who worked in the Wright brothers' bicycle shop, built the engine for the 1903 Wright Flyer, generally considered the world's first powered airplane that actually flew. The engine was a 12-horsepower, four-cylinder internal-combustion model weighing 170 pounds.

Taylor purchased some of the parts he needed. The ignition switch came from the local hardware store. Parts that needed to be cast from molten metal were ordered from a foundry. Otherwise, Taylor used the tools in the Wrights' shop. For example, their lathe bored the holes for the pistons. The shop was set up for metalworking because when the Wrights were not refining their flying machines, they designed and built custom bicycles.

It took Taylor six weeks to make the engine. However, he did not invent the internal combustion engine. Such engines had been around for four decades and were being used in automobiles when the Wrights were building their Flyer. The Wrights wrote to a dozen automobile companies but could not find an engine that was sufficiently light and powerful.

The engine was very simple by today's standards. Gasoline was fed into the engine via gravity from a fuel tank attached to a wing. There was no carburetor and no spark plugs, and the engine tended to stall.

It is especially impressive that the Wright Flyer took to the sky while its main compet.i.tion, Samuel Langley's Aerodrome, which had a considerably more powerful engine, failed. The Wrights' advantage stemmed from the very scientific approach they took toward designing an airplane.

Unlike other aspiring aviators of the time, the Wrights realized that they would need to control the airplane's pitch (up-and-down movement), yaw (side-to-side movement), and roll (rotation around an axis running the length of the plane). They built and tested a series of gliders beginning in 1899 and carefully noted the effects of each change they made. They even created their own wind tunnel to test small-scale models of different types of wings.

It took many crashes and improvements of their successive gliders before they felt ready to add a motor. Then, Taylor's motor, despite its limitations, permitted the Wrights to make history.

Off-kilter When you hold up a carpenter's level, with the bubble in the middle, what is it level to? The Earth is round, so how can anything be level?

When the bubble is centered, the carpenter's level is parallel to a tangent to the Earth at that location. A tangent is a straight line that touches a sphere at just one point. It makes a 90-degree angle with the radius of the sphere at that point.

Since Earth is a b.u.mpy sphere, the tangent is not always parallel to the ground itself. On a hillside, the tug of gravity is still toward the center of the planet, so the level is aligned when it is perpendicular to a line to the Earth's center.

Architecture by numbers How were the ancient Romans able to engineer and build all their magnificent buildings using their unwieldy number system?

Roman architecture borrows both principles of design and methods of construction from the Greeks. However, it is the Romans' adoption of concrete as a standard technique of construction that revolutionized architecture. Concrete permits more imaginative design because it can be poured, and because it is strong enough to span vast distances.

Up until the last two centuries, structures were designed and built based on prior experience. A concept would be tried, and if it worked, variations of the concept might be employed for generations. Catastrophic failures were not uncommon, but architects and engineers learned from the failures and modified their designs accordingly.

The Romans used mathematics to design their buildings, particularly geometry and systems of proportions. However, only much more recently has mathematics been used to design buildings by taking into consideration the mechanical properties of the materials being used and the loads acting on a structure. These calculations require calculus, which was not developed until the 17th century.

Had the Romans needed more sophisticated mathematics to design their buildings, their number system might have been a constraint, but lifelong experience with Roman numerals would have made them seem a lot less c.u.mbersome to them than they do to us.

2. Chemical concoctions

Sticky situations

I heard on some science TV show that no one knows for sure what makes glue work. Is this true? What does make glue stick? Does it depend on the type of glue? What do glues have in common?

We take sticky notes, glue sticks, Super Glue, and tape so for granted that it may come as a surprise that developing new adhesives is a very active area of research. Understanding what makes stuff sticky is key to making stickier adhesives or adapting them to new purposes.

Although people use the words glue and adhesive interchangeably, glues, which are made from natural materials, have been around a lot longer than adhesives, which are made from synthetic materials. According to archaeologists, ancient civilizations used sticky materials like tree sap to repair broken pottery as far back as 4000 B.C. Beeswax and tar were long used to seal gaps between planks in ships, and for centuries other glues have been made from fish, animal hides, and hooves.

White glues (adhesives), such as Elmer's, work by evaporation. As the water in Elmer's evaporates, the polyvinyl acetate latex that has spread into the crevices of the material being glued forms a pliable bond.

Super Glue has as its main ingredient a chemical called cyanoacrylate. The presence of water causes cyanoacrylate molecules to start linking with each other until they form a strong plastic mesh. Super Glue is all-purpose because pretty much everything has trace amounts of water on its surface.

Sticky notes are easily removable and restickable because the adhesive on the back of the notes consists of a thin, b.u.mpy layer of microspheres. These little spheres stick to a surface, but the gaps between the spheres remain unstuck. In comparison to the pebbled appearance of the adhesive on the notes, the adhesive on tape looks flat and uniform under an electron microscope.

Even with synthetic sticky materials, scientists still have a thing or two to learn from Mother Nature. Geckos, with their amazing ability to run up walls, have been a recent source of inspiration. Geckos have about 500,000 microscopic hairs, called setae, on each foot. At the end of each seta are 1,000 branches tipped with pads called spatulae.

Unbalanced electrical charges around molecules in the spatulae and molecules in the surface to which the gecko is clinging interact, drawing the molecules together. These interactions, known as van der Waals forces, occur because electrons are mobile. At any instant, more electrons may be at one end of a molecule, giving that end a temporary negative charge, and the other end a temporary positive charge. This charge separation induces a movement of electrons in nearby molecules so that the charges fluctuate in synchrony, and the attraction is maintained over large numbers of molecules. Van der Waals forces, summed over the millions of spatulae in each foot, create a very strong bond.

Using this knowledge, researchers have developed a super-sticky material with "nan.o.b.u.mps" that resemble the spatulae on geckos' toes. If it could be ma.s.s-produced, this material could be made into reusable tape that even works underwater.

Strong bond Why is the adhesiveness of white glues, such as Elmer's, stronger than that of glue sticks?

The sticky molecules in Elmer's all-purpose glue are mixed with water, which allows the glue to penetrate into tiny gaps on an object's surface. When the water evaporates, the sticky molecules remain behind and form many anchor points all over the surface. On the other hand, a glue stick glides over the pores and applies glue only to the b.u.mps, resulting in fewer anchors.

The adhesive molecules in Elmer's and glue sticks are different, but they bond in similar ways (unlike Super Glue, which chemically reacts with water to form a highly interlinked mesh of molecules). However, the ingredients used to solidify a glue stick and help it glide over a surface reduce its adhesive strength.

Black gold How do you get gasoline, kerosene, and other products from crude oil? Also, how is it possible to make gasoline from corn?

Crude oil, when recovered from an oil well, consists of a complex mixture of hydrocarbons-molecules made from hydrogen and carbon atoms. To make products of value from this mixture, hydrocarbons of different sizes are separated via distillation.

This involves heating crude oil to over 1,000 degrees Fahrenheit (540 degrees C) at the base of a fractionating column-a tower 260 feet (80 meters) high with a series of collecting trays at different heights. The hydrocarbon vapor cools as it moves up the column and condenses on the trays. Larger hydrocarbons condense on the trays near the base of the column, and smaller hydrocarbons condense on the higher plates.

Methane, ethane, propane, and butane (which have one, two, three, and four carbons, respectively) are collected from the very top of the column. They can be bottled and sold. Since they are odorless, smelly sulfur compounds are added for safety reasons.

The fractions condensing on lower trays include gasoline, kerosene, gas oil (used for diesel fuel and heating oil), and lubricating oil. The very large hydrocarbons that do not boil off are redistilled at low pressure to separate waxes, tar, and so on.

Subsequent processing steps depend on consumer demand. For example, to increase the yield of gasoline from crude oil, small hydrocarbons can be linked to form longer ones, and large hydrocarbons can be "cracked" into smaller ones. Hydrocarbons are also the starting materials for plastics, herbicides and pesticides, detergents, textiles such as acrylic and polyester, dyes, and cosmetics.

Gasoline, by the time you pump it into your vehicle, is a complex mixture of 200 chemicals added to improve performance and help fuel burn more cleanly. For instance, hydrocarbons of different lengths and structures are added to boost the fuel's octane rating. This reduces "knocking," which occurs when gasoline ignites spontaneously by compression, instead of by the spark from the spark plug.

In the past, tetraethyl lead was also added to reduce knocking. It was banned because of health risks and largely was replaced by methyl tert-butyl ether (MTBE). Now ethanol is replacing MTBE because of health concerns over the latter.

Ethanol is the fuel that is produced from corn or other starches or sugars. It is made in the same way as moonshine, by crushing and fermenting the grain, followed by distillation. Most engines can run on a mixture of up to 10 percent ethanol in gasoline, and "flexible fuel vehicles" can accommodate blends of up to 85 percent ethanol.

What's in a name?

Does it matter what brand of fuel you use in your car, insofar as engine performance and gas mileage are concerned?

Gasoline suppliers share pipelines, and different distributors fill up their tanks at the same terminals. Therefore, the gasoline itself is the same. The only difference between brands is the additives blended with the gasoline when it is loaded into tankers destined for a retail station. Major brands advertise that they use more or better-quality additives to control corrosion and the formation of deposits in the engine and fuel supply system.

However, an American Petroleum Inst.i.tute representative was unaware of any independent testing that shows which brands are superior. In addition, since 1995, the U.S. Environmental Protection Agency has mandated the use of detergents in gasoline and has set performance standards to ensure that the detergents control engine deposits. Control of deposits enhances fuel economy and reduces pollutants in engine exhaust.

Under the Clean Air Act and its amendments, the composition of gasoline has undergone many changes. First was the phaseout of leaded gasoline. Average blood lead levels in the United States declined dramatically over the 15 years that the use of leaded gasoline dropped from its peak to near zero, reports the Centers for Disease Control and Prevention.

Later came the introduction, in the most polluted cities, of reformulated gasoline with more oxygen to increase fuel combustion. Oxygen content is increased through the use of oxygenates. Initially methyl tert-butyl ether (MTBE) was used, but due to health concerns it is being replaced by ethanol. Reformulated gasoline has lower levels of benzene, a known carcinogen, and other pollutants. Fuel reformulation is determined by federal and local mandates, rather than by brand.

Fuel reformulation is not the only factor responsible for reductions in pollutants. A decade-long study of tailpipe emissions, published in the journal Environmental Science and Technology Environmental Science and Technology, determined that reductions in three major pollutants-carbon monoxide, nitrogen oxides, and hydrocarbons-were mainly the result of improved onboard vehicle emission control systems. The researchers found similar emissions improvements in cities that mandated reformulated fuel and those that did not.

Since the composition of the different brands of fuel varies little, many companies have tried to attract consumers by advertising their green credentials. For the Sierra Club's environmental rankings of oil companies, see www.sierraclub.org/sierra/pickyourpoison.

Auto alternatives As the world supply of fossil fuels dwindles, what alternatives to gasoline for vehicles are being researched or developed?

These days, the buzzword is biofuels-fuels derived from organic matter. The two most common biofuels are bioethanol and biodiesel. Bioethanol is made from starchy or sugary crops in the same process that yields homemade liquor. Yeast ferments sugar into ethanol, which is distilled to remove water. Biodiesel is made from vegetable oils or animal fats.

The United States has been ramping up production of ethanol from corn, but this cannot replace imported petroleum. Global corn prices have already increased as grain is being diverted from food chain to fuel tank. Corn is a difficult crop to grow, requiring high inputs of fertilizer and pesticides. According to some pessimistic estimates, it requires nearly as much energy to cultivate corn and convert it to ethanol as is obtained from the ethanol in the end.

On the other hand, there is a great deal of excitement about technologies to make ethanol from cellulose. Cellulose, the main structural component of plants, consists of long chains of sugars. An efficient process to convert cellulose into its component sugars would make feasible the production of ethanol from straw, crop waste, wood chips, and maybe even sc.r.a.p cardboard and paper.

Hydrogen is another alternative source of energy for locomotion. Hydrogen can be burned or converted into electricity through fuel cells. Prototype hydrogen cars exist, but perversely, the hydrogen being used to power them is usually derived from natural gas. Hydrogen can be made by splitting water, but this requires a large input of energy. Storing and transporting hydrogen are also problems to be solved if hydrogen cars are ever to become practical.

Battery-powered electric vehicles are constantly improving. The major challenge in making them commercially viable is developing a battery that can power a vehicle for long distances, can be recharged repeatedly, and is not prohibitively expensive. The popular hybrid cars get around the limitations of batteries by combining gasoline power and electric power. Also, during braking, the electric motor in a hybrid car acts as a generator to recharge the batteries.

Hydrogen and batteries are essentially ways to store energy from other sources so that it can be used to move a vehicle. Other methods of energy storage are possible. For example, energy can be used to pump air into the pressurized tank of a compressed-air car. The expansion of air then moves the pistons in the engine. The car's emissions are clean, but, of course, the actual emissions depend on how the energy used to compress the air was produced. Prototype compressed-air cars exist, but research is ongoing to bring them from concept to market. The greatest challenge is creating a car that can achieve a useful driving range on a single tank of compressed air.

Sugar high I have heard that sugarcane is five to ten times more efficient than corn in the production of ethanol. Is this true? If so, why isn't it being promoted?

Producing ethanol from sugarcane in Brazil is roughly seven times more efficient (with respect to the ratio of energy output to fossil fuel input) than producing ethanol from corn in the United States. However, more than this one statistic is needed to compare these two technologies.

Brazil's sugarcane ethanol program began 30 years ago during the oil crisis. The government adopted mandatory regulations on the amount of ethanol to be mixed with gasoline, and it subsidized ethanol production, mainly through taxes on gasoline. Now Brazil is the world's largest exporter of ethanol, and Brazilian ethanol is compet.i.tive with gasoline in international markets.

Sugarcane prefers warm climates, and in the United States the largest sugarcane producers are Florida, Louisiana, Hawaii, and Texas. American farmers also grow sugar beets in states with temperate climates. Currently, none of this sugar gets fermented into ethanol.

We eat all the sugar we produce, and we import another 20 percent of the sugar we consume. On average, each year every American gobbles down more than 40 pounds of refined sugar, nearly 45 pounds of corn-derived sweeteners, and just over a pound of honey and syrup. Annual per-capita sweetener consumption is the equivalent of about seven gallons of ethanol.

Because of the high cost of sugar in the United States, the domestic production of ethanol from sugar is not economically compet.i.tive with the production of ethanol from corn, according to data from the U.S. Department of Agriculture.

Brazil has an ideal climate for growing sugarcane, as well as low sugar prices. Despite these advantages, Brazil had a 15-year "learning curve" before its ethanol became cost-compet.i.tive with gasoline.

One reason for the efficiency of Brazilian sugarcane ethanol is that baga.s.se-the residue from sugarcane processing-is burned to provide heat for the distillation and electricity to run the machinery. Corn stover-stalks and leaves-could be used for this purpose, but it is not usually harvested.

The efficiency of corn-based ethanol could also be improved with the development of corn varieties that have higher starch content, or better enzymes to process the starch into sugar. In the meantime, the United States is protecting its corn-based ethanol industry with an import duty of 54 cents per gallon levied on Brazilian ethanol.

Both technologies raise concerns about the clearing of wild land for agriculture and the use of food to fuel vehicles.

Water fire I received a video clip from a friend that deals with the use of water as an alternative to fossil fuels. Does this seem plausible to you? Neither of us can figure out why we haven't heard of this before. It seems too good to be true.

The water-as-fuel hype recurs periodically. For instance, an Indian chemist convinced his local government that he powered his scooter on fuel made by boiling herbs in water. Then there was Stanley Meyer's "water-powered car." An Ohio court ordered Meyer to repay investors after it found him guilty of "gross and egregious fraud."

One of the latest incarnations of water hype is a story on YouTube by a Cleveland-based television reporter about burning water. No, it is not the famous fire on Cleveland's once grimly polluted Cuyahoga River, which helped spur the environmental movement. The video shows clean salt.w.a.ter going up in flames.

The demonstration is not a hoax, but salt.w.a.ter won't reduce our dependence on other sources of energy. The adage "If it sounds too good to be true, it probably is" makes good sense. In order to burn, the water must be exposed to a strong, focused field of radio waves. When the field is turned on, the water burns. When it is switched off, the water stops burning.

In other words, unlike fossil fuels, water requires a constant input of energy to make it burn. No one has yet published an a.n.a.lysis that compares how much energy is recovered from burning the water versus how much is used to create the radio frequency field. However, it is impossible to extract net energy. It would violate the laws of thermodynamics and provide the basis for a perpetual-motion machine.

Water burns in the radio frequency field because it is being dissociated into hydrogen and oxygen, which are recombined by burning. The exact mechanism by which the field breaks bonds in water is under dispute, but the end result is similar to conventional electrolysis. Electrolysis uses an electric current to produce hydrogen and oxygen at separate electrodes, and more energy is used than is produced by burning the resultant hydrogen.

If using a radio frequency field to split water turns out to be more efficient than electrolysis, this new discovery could be of practical interest. Producing hydrogen from water is a way to store energy. If the sun is the source of energy to liberate hydrogen from water, the result is a clean-burning fuel produced by a renewable energy source.

Periodic-table personalities Why are nuclear bombs so powerful? I know it has something to do with the splitting of an atom, but why does that cause such catastrophic damage?

There are two main types of nuclear bombs. In a fission bomb, large, unstable atoms (uranium or plutonium) split into smaller, more stable atoms. In a fusion bomb, also called a thermonuclear or hydrogen bomb, the nuclei of very small atoms combine to form larger, more stable atoms.

The binding energies that hold together the protons (positively charged particles) and neutrons (neutral particles) in the nucleus of an atom are approximately a million times stronger than the binding energies that hold together atoms in a molecule. Therefore, nuclear bombs are much more powerful than conventional bombs, in which chemical reactions-rearrangements of atoms in molecules-cause the explosion.

It might seem counterintuitive that opposite processes (splitting apart an atomic nucleus and fusing two nuclei) can both release energy. Whether fission or fusion releases energy depends on the size of the nucleus.

As atomic nuclei become larger, they grow more stable because of the strong nuclear force between nuclear particles. Atoms near iron (the 26th element) in the periodic table have the most stable nuclei. However, as atomic nuclei increase in size compared to iron, they become less stable, because there are more positively charged protons, which repel each other.

The more stable nuclei created by the fission of atoms larger than iron, or through the fusion of small atoms, have less ma.s.s than the original nuclei. The missing ma.s.s is transformed into energy, a process expressed mathematically by Einstein's famous equation E=mc2.

Jolt-free beans How is coffee decaffeinated?

The three main decaffeination processes are solvent decaffeination, decaffeination with carbon dioxide, and Swiss Water decaffeination. All three processes involve soaking the beans in chemicals to extract the caffeine.

Caffeine was first discovered and isolated in the late 19th century, and the first process to decaffeinate coffee, solvent decaffeination, was developed in Germany in 1900. The solvent is the liquid in which the coffee beans are soaked to remove the caffeine.

An ideal solvent removes the caffeine without removing compounds that give coffee its flavor and aroma. Many different (not always healthful) chemicals have been used to decaffeinate coffee, including alcohol, acetone, benzene, and methylene chloride, which was the preferred solvent until it was implicated in the depletion of the ozone layer. Ethyl acetate, a chemical that occurs naturally in some fruit, is now the preferred solvent.

In solvent decaffeination, the unroasted beans are steamed to make the beans more porous and the caffeine easier to extract. The beans are exposed to the solvent to dissolve the caffeine, and then they are rinsed, dried, and roasted.

Carbon dioxide decaffeination was patented in the early 1970s. In this method, carbon dioxide gas is compressed into a liquid at 50 times atmospheric pressure and is used as the solvent to extract caffeine. This method is particularly good at removing caffeine without removing flavor compounds, but a drawback is that it is expensive to build and maintain a carbon dioxide decaffeination plant. So the method is feasible for only large coffee producers.

Swiss Water decaffeination was patented in 1938 but was not commercialized until the late 1970s. In this process, coffee beans are soaked in hot water, which extracts the caffeine but also many of the flavor compounds. The water is pa.s.sed through an activated carbon filter to remove the caffeine. Initially, the decaffeinated water was sprayed back on the beans after they had been partially dried to allow them to reabsorb the flavor compounds.

In the last 20 years, this procedure has been refined; now the caffeine-free water with the flavor compounds is used to remove caffeine from subsequent batches of beans. Since the water is already saturated with coffee flavor, the flavor compounds stay in the beans, but the caffeine is extracted.

Caffeine is one of many substances plants make to defend against insect attack. But the recent discovery of a caffeine-free variety of coffee related to commercially viable strains might ultimately permit plant breeding to render chemical decaffeination processes obsolete.

Decaf danger?

I was surprised to read about the chemicals once used in decaffeination, such as benzene, which I believe has been known (however, not really proven) to cause leukemia. Do I have the right chemical?

You are correct; benzene is a known carcinogen. Early efforts to decaffeinate coffee employed a number of other solvents now known or suspected to cause cancer, including chloroform, carbon tetrachloride, trichloroethylene, and methylene chloride.

In spite of this, even for those who were imbibing decaf before the newer methods of decaffeination started to emerge in the late 1970s, there is no evidence to suggest reason for alarm.

Only a very small amount of solvent (around one part per million) remains after the beans are rinsed and roasted. Methylene chloride, which was popular longer than the other solvents listed, appears to cause cancer in animals only when given in high doses (4,000 parts per million).