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In organisms that maintain a constant shape and have one dimension longer than the other, at least two directional terms can be used. The long or longitudinal axis is defined by points at the opposite ends of the organism. Similarly, a perpendicular transverse axis can be defined by points on opposite sides of the organism. There is typically ...
Examples: The thumb is on the radial side of the hand (the same as saying the lateral side); the ulnar side of the wrist is the side toward the little finger (medial side). Ventral and dorsal , which describe structures derived from the front (ventral) and back (dorsal) of the embryo , before limb rotation.
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms.It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology ...
For example, in a typical gene a start codon (5′-ATG-3′) is a DNA sequence within the sense strand. Transcription begins at an upstream site (relative to the sense strand), and as it proceeds through the region it copies the 3′-TAC-5′ from the template strand to produce 5′-AUG-3′ within a messenger RNA (mRNA).
A significant example of directional selection in populations is the fluctuations of light and dark phenotypes in peppered moths in the 1800s. [16] During the industrial revolution, environmental conditions were rapidly changing with the newfound emission of dark, black smoke from factories that would change the color of trees, rocks, and other ...
In molecular biology and genetics, upstream and downstream both refer to relative positions of genetic code in DNA or RNA.Each strand of DNA or RNA has a 5' end and a 3' end, so named for the carbon position on the deoxyribose (or ribose) ring.
This is largely because the results of disruptive selection are less stable than the results of directional selection (directional selection favors individuals at only one end of the spectrum). For example, let us take the mathematically straightforward yet biologically improbable case of the rabbits: Suppose directional selection were taking ...
Chemotaxis refers to the directional migration of cells in response to chemical gradients; several variations of chemical-induced migration exist as listed below. Chemokinesis refers to an increase in cellular motility in response to chemicals in the surrounding environment.