A Hurricane In Brazil?

Hurricanes are terrifying. They rip trees right out of the ground, hurl cars into the air, and flatten houses. Their winds can blow faster than 100 mph. Some hurricanes have been known to pull a wall of water from the ocean 20 feet high ... then fling it inland, inundating miles of coast. No other storms on Earth are so destructive. Or so ...

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What Is The Periodic Table?

The periodic table of the elements is a representation of all known elements in an orderly array. The periodic law presented by Dmitri Mendeleev in 1869 stated that if the (known) elements are ... Continue reading


Leaps and Bounds

Leap years are years with 366 days, instead of the usual 365. Leap years are necessary because the actual length of a year is 365.242 days, not 365 days, as commonly stated. Basically, leap years ... Continue reading


The First Starlight

Imagine being able to see our Universe 14 billion years ago when it was just a baby. If we had a time machine, we could go back and watch how its infant features emerged after the Big Bang. There are ... Continue reading


Man Made Clouds

There are many different types of clouds in the sky, but did you know that some of them are man-made? 'Contrails' are the long, thin clouds that are left by airplanes as they fly past. Contrails ... Continue reading


Genome Mapping: A Guide To The Genetic Highway We Call The Human Genome

GenomeMappingHumanGenomeImagine you're in a car driving down the highway to visit an old friend who has just moved to Los Angeles. Your favorite tunes are playing on the radio, and you haven't a care in the world. You stop to check your maps and realize that all you have are interstate highway maps--not a single street map of the area. How will you ever find your friend's house? It's going to be difficult, but eventually, you may stumble across the right house. This scenario is similar to the situation facing scientists searching for a specific gene somewhere within the vast human genome. They have available to them two broad categories of maps: genetic maps and physical maps. Both genetic and physical maps provide the likely order of items along a chromosome.

However, a genetic map, like an interstate highway map, provides an indirect estimate of the distance between two items and is limited to ordering certain items. One could say that genetic maps serve to guide a scientist toward a gene, just like an interstate map guides a driver from city to city. On the other hand, physical maps mark an estimate of the true distance, in measurements called base pairs, between items of interest. To continue our analogy, physical maps would then be similar to street maps, where the distance between two sites of interest may be defined more precisely in terms of city blocks or street addresses. Physical maps, therefore, allow a scientist to more easily home in on the location of a gene. An appreciation of how each of these maps is constructed may be helpful in understanding how scientists use these maps to traverse that genetic highway commonly referred to as the 'human genome'.

Just like interstate maps have cities and towns that serve as landmarks, genetic maps have landmarks known as genetic markers, or 'markers' for short. A marker may be used as one landmark on a map if, in most cases, that stretch of DNA is inherited from parent to child according to the standard rules of inheritance. Markers can be within genes that code for a noticeable physical characteristic such as eye color, or a not so noticeable trait such as a disease. DNA-based reagents can also serve as markers. These types of markers are found within the non-coding regions of genes and are used to detect unique regions on a chromosome. DNA markers are especially useful for generating genetic maps when there are occasional, predictable mutations that occur during meiosis--the formation of gametes such as egg and sperm--that, over many generations, lead to a high degree of variability in the DNA content of the marker from individual to individual.