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  Home >> Genetics Dictionary >> Operon - Ozone layer

Operon
A set of genes transcribed under the control of an operator  gene.

2. A genetic unit in prokaryotes that consists of one or more structural genes (polypeptide-encoding) adjacent to an operator region that controls their transcription.

3. A unit consisting of one or more cistrons that function coordinately under the control of an operator gene.

Order
The taxonomic classification level between class and family. For example, within the class Mammalia, there are several orders, including the meat-eaters, who make up the order Carnivora; and the insect-eaters, grouped together in the order Insectivora. The orders in turn are divided into families; the order Carnivora includes the families Felidae (the cats), Canidae (the dogs), and Ursidae (the bears), among others. See also taxon.

Ordered spores
A linear sequence of four haploid meiotic spores (or pairs of spores produced by a post-meiotic division) within a fungi ascus; this arrangement allows identification of chromatids participating in crossover events.

Organelle

Any of a number of distinct small structures found in the cytoplasm (and therefore outside  the nucleus) of eukaryotic cells (e.g., mitochondrion and chloroplast).

Organisms
Living things.

Orthogenesis
The erroneous idea that species tend to evolve in a fixed direction because of some inherent force driving them to do so.

Outbreeding
The crossing of genetically unrelated plants or animals.

Owen, Richard
A 19th-century British comparative anatomist, who coined the word “dinosaur” to describe a breed of large, extinct reptiles. He was the first to propose that dinosaurs were a separate taxonomic group. Owen opposed Darwin’s theory of evolution, but ultimately his work helped support evolutionary arguments.

Ovulation
Th  release of an egg from the ovary into the fallopian tube to be fertilized by a sperm about mid-point in a woman’s 28 day menstrual cycle.

Ozone layer
The region of the atmosphere, generally 11-26 km (7-16 miles) above Earth, where ozone forms in high concentrations. The ozone layer absorbs ultraviolet radiation, shielding Earth from its damaging effects.

 

 

 

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