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a variation, or form of a gene found at specific genetic locus. Genetic variation comes from the presence of different combinations of allele*s in different individuals. Organisms contain one allele for each of their sets of chromosomes. Diploid organisms, such as humans, have two sets of chromosomes and therefore, two alleles for each gene. An organism's genotype* is a description of the alleles present at specific genetic loci.
The maximum displacement of a wave* form measured relative to the resting position of the medium through which the wave is moving. The amplitude* of a wave is measured in the orientation of particle movement. In longitudinal waves the amplitude is measured in the same orientation as energy propagation. For transverse waves, it is measured perpendicular to energy propagation.
The amplitude of pendulum is the distance between the bob's resting position and its position at maximum displacement.
Physical waves are often described using wave height instead of amplitude. A wave's height is equal to 2 times its amplitude.
- Angle of reflection
The angle formed between a reflected light ray and a line normal* to the point where the light ray hit the surface it is reflecting off of.
- complete dominance
The amount of solute present in a volume* of water or other solvent. For chemicals, common units for concentration* are weight*/volume percent, weight percent and molarity. For biologically active compounds such as antibodies or enzymes, concentrations are often reported in activity units/ml. Concentration of bacterial and cell cultures are often reported in cells / ml or colony forming units (CFU) per ml.
- covalent bond
A chemical bond between two atoms in which the atoms completely share one or more pair of electrons.
- Critical Angle
in optics, the angle of incidence between a light ray and an interface above which the ray reflects completely instead of passing through the interface from one medium to the other. The complete reflecion of the light ray is referred to as total internal reflection.
The critical angle is a funcion of the index of refraction of the two media.
With the Snell's Law equation solved for the angle of incidence:
θi = arcsin[ sin( θr ) × nr ÷ ni ]
θr = the angle of refraction
θi = the angle of incidence
ni = the refraction idex of medium containing the incident ray
nr = the refraction idex of medium containing the transmitted ray
The critical angle is the value for θi at which θr equals 90 degrees (1.57 radians):
θi = arcsin[ sin( 90 ) × nr ÷ ni ]
Total internal reflection occurs when the θr exceeds 90 degrees (1.57 radians).
- diurnal tide
A tidal pattern characterized by a single tidal cycle of one high tide and one low tide every day.
The orbit of the Moon drives the tidal period*. The Moon goes around the Earth once every 24 hours and 50 minutes resulting in high and low tides occurring about an hour later each day.
Diurnal tide*s are one of the three commonly described tidal patterns. The other two common tidal patterns involve two tidal cycles per day.
an abbreviation for Deoxyribonucleic Acid, the material that carries the heritable information living organisms need to synthesis the many enzymes and proteins required for life.
- Electromagnetic Spectrum
A term used to describe the entire range of electromagnetic radiation from long wavelength*, low frequency*, low energy radio waves on one end to short wavelength, high frequency, high energy gamma rays at the other. Visible light* covers a small range in the middle of the spectrum.
Visual depictions of the electromagnetic spectrum* are usually shown on a log scale to allow the visualization to encompass the entire range of values which, cover many, many orders of magnitude. For example, electromagnetic energy wavelengths range from 10’s to 100’s of meters for radio waves, down to femtometers for gamma rays.
- Electromagnetic wave
The movement of electromagnetic energy. Electromagnetic energy arises from interactions between electric and magnetic fields. The fact that the energy is associated with this interaction and not with disturbances in a physical medium is why electromagnetic wave*s can travel through a vacuum.
In math, a number placed above and to the right of another number indicating the number of time that number should be multiplied by itself. For example the number three with an exponent* of two, indicates that three should be multiplied by itself two times.
32 = 3 × 3 = 9
The exponent is also called the power the number is raised to. Negative exponents indicate that a number should be multiplied by one over itself which is the same as dividing.
- Genetic Drift
Changes in allele* frequency* in a population due to chance events. Genetic drift* is caused by some individuals in a population producing more offspring than others. This causes allele frequencies to diverge from the frequencies expected assuming even representation from generation to generation.
Genetic drift is an evolutionary force because it causes changes in the genetic structure of populations over time. However, the changes are not adaptive in the way that changes due to natural selection* are.
The influence of genetic drift increases as population size decreases. In relatively large populations, small random changes in allele frequencies are negligible relative to the entire population. In small populations, changes driven by genetic drift can be significant. In the extreme case, it can result in the complete loss of specific alleles from a population.
The basic unit of heredity in living things. Many individual genes specify information about specific traits such as hair color in animals or leaf shape or color in plants.
A description of the allele*s present in an organism. The term is also used to describe the set of alleles at specific genetic loci. Alleles are often distinguished from each other by case sensitive abbreviations. Dominant allele abbreviations begin with capital letters and recessive allele abbreviations begin with lower case letters.
- Incomplete dominance
- Longitudinal wave
- Lunar tide
- The component of the tide caused by the gravitational attraction between the Moon and water on Earth. The Moon-Earth system rotates around its center of gravity once every 24 hours and 50 minutes. This rotational period* drives the daily tidal period on much of the planet.
The amount of matter in an object. On the earth, the weight* and mass* of an object are equivalent. However the distinction becomes important for very precise measurements or when discussing object not no the earth.
- Natural Selection
A non-random process by which some genotype*s contribute more offspring to the next generation than other genotypes. Uneven representation arises from differences in life history traits such as reproductive success or survival.
A line perpendicular to a surface is normal* to that surface. On a curved surface, the normal is a line perpendicular to a line tangent to the curve at a particular point.
Normals have many uses in mathematics and physics. In optics, for example, the normal line is used to calculate angels of reflection* and refraction* for light rays encountering surfaces and interfaces.
Nucleotides are synthesized from nucleoside*s by the addition of one or more phosphates to the number 5 carbon of the sugar.
In addition to their role in RNA and DNA, nucleotides participate in cellular metabolism and signaling.
The amount of time over which a wave* form repeats itself. Period* is reported in the units of seconds. The inverse of the period of a wave or other repeating cycle is its frequency* (frequency = cycles / second).
- Physical wave
- Purine Base
A nitrogenous base that has a double ring structure made up of a five-atom ring attached by one side to a six-atom ring. The two rings contain a total of five carbon and four nitrogen atoms. Biologically significant purines include the bases adenine and guanine.
When bound to a ribose or deoxyribose sugar and a phosphate molecule, these bases form two of the five nucleotide building blocks of DNA* and RNA
- Pyrimidine Base
A nitrogenous base that has a six membered ring. The ring contains four carbon and two nitrogen atoms. Biologically significant pyrimidines include the bases thymine, cytosine and uracil.
When bound to a ribose or deoxyribose sugar and a phosphate molecule, these bases form three of the five nucleotide building blocks of DNA* and RNA.
A change in direction of light or other energy wave*s when they encounter surfaces. For light rays reflecting off of a flat surface, the law of reflection* states that the angle of reflection* is equal to the angle of incidence.
Reflection is one of the three things that can occur when a light ray encounters an interface between two media. The other two things that can occur are that the energy can transmit into the new medium or be absorbed.
The amount a wave bends depends on the angle at which it encounters the interface. This relationship is described by Snell’s Law. The greater the angle of incidence, the larger the amount of refraction*. A wave that encounters a surface with an angle of incidence of zero does not refract.
- scientific notation
A convenient format for writing very small and very large numbers. The format contains a decimal fraction multiplied by ten raised to a power
- Solar tide
The component of the tide caused by the gravitational attraction between the Sun and water on Earth. There are two water bulges associated with this gravitational attraction. One in the direction of the sun and another on the opposite side of the Earth.
The period* of the solar tide*s is driven by the rotation of the Earth around its own axis which occurs once every 24 hours. The interaction between the solar and lunar tides cause the monthly spring/neap tidal cycle.
- Surface wave
A wave* that travels along the boundary between two media. Particles in the medium move in a circular path as the wave passes by. Motion is greatest at the boundary and diminishes with distance from the boundary.
- Transverse wave
A wave* in which the displacement of the particles (or medium) is perpendicular to the direction the wave is traveling. Unlike longitudinal wave*s, these waves require solid material. They do no move through liquids or gases.
- Visible light
The range of electromagnetic radiation visible to the human eye. It is a narrow portion of the electromagnetic spectrum* encompassing energy with wavelength*s from around 400 nm (blue light) to 700 nm (red light).
The visible range of the electromagnetic spectrum is flanked by shorter wavelength ultraviolet energy on one side and the longer wavelength near-infrared energy on the other. Visible light* includes energy in the range of the sun’s peak output which is roughly 480 nm (yellow light).
The amount of three dimensional space an object occupies.
A movement or oscillation that spreads from a defined point. There are two types, physical wave*s and electromagnetic wave*s. Physical waves require a medium through which to propagate. Electromagnetic waves do not. When a wave moves, energy is propagated, not the medium through which the wave travels.
The distance over-which a wave*’s shape repeats. For transverse wave*s, the wavelength* is often drawn as a line from wave crest to wave crest, but it does not need to be. The wavelength is is the horizontal distance between successive crests, troughs or any other equivalent point between neighboring waves.
The fact that wavelength can be measured as the distance between any corresponding points on adjacent waves important for longitudinal wave*s, which lack crests and troughs. For these waves, wavelength can be shown as the distance between neighboring regions of compression.
As a distance, wavelengths are usually reported in meters with or without a prefix (kilo, micro, nano, etc).
the force created when a mass* is acted on by an external force such as gravity