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Human penis. In human anatomy, the penis ( / ˈpiːnɪs /; pl.: penises or penes; from the Latin pēnis, initially "tail" [ 1]) is an external male sex organ ( intromittent organ) that serves as a passage for excretion of urine and ejaculation of semen. The main parts are the root, body, the epithelium of the penis including the shaft skin, and ...
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 ...
Erection. Three columns of erectile tissue make up most of the volume of the penis. An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors ...
Cladistics. Cladistics ( / kləˈdɪstɪks / klə-DISS-tiks; from Ancient Greek κλάδος (kládos) 'branch') [ 1] is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived ...
Karyotype. A karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. [ 1][ 2] Karyotyping is the process by which a karyotype is discerned by determining the chromosome complement of an individual, including the number of ...
Reversal – is a loss of derived trait present in ancestor and the reestablishment of a plesiomorphic trait. Convergence – independent evolution of a similar trait in two or more taxa. Apomorphy – a derived trait. Apomorphy shared by two or more taxa and inherited from a common ancestor is synapomorphy. Apomorphy unique to a given taxon is ...
Intermediate minor rankings are not shown. In biological taxonomy, a domain ( / dəˈmeɪn / or / doʊˈmeɪn /) ( Latin: regio [1] ), also dominion, [2] superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together. It was introduced in the three-domain system of taxonomy devised by Carl Woese, Otto Kandler and ...
Stabilizing selection (not to be confused with negative or purifying selection) is a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value. This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time.