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;; Home >>Botany Dictionary >> Pleiotropy - Population
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Pleiotropy - The production of more than one physiologically uncorrelated effect by one gene. It is attributed to one gene initiating two or more chains of reactions.
Pleiotropism - The condition when one factor is having an effect; simultaneously on more than one character in the offspring.
Pleistocene - Refers to a geological period which was lasting approximately from 1 million to 10,000 years ago. During it the four major Ice Ages occurred.
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Plerome - Refers to the central core of tissue in the growing point of a stem or root of vascular plants. It gives rise to the vascular cylinder and pith.
c - Describing a primitive character state, the origin of which could be traced back to a remote ancestor.
Pleurocarpous - Refers to mosses in which reproductive organs are produced laterally and main axis is generally creeping.
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Pleuropneumonia Like Organisms (PPLO) - Including members of order Mycoplasmatales. They are extremely small parasitic micro-organisms, some only 100 nm in diameter, gram negative, mostly non-motile and not having a rigid cell wall, mostly require sterols for growth and considered to be responsible for certain yellows diseases of plants, also in witches' broom of alfalfa and maize stunt. They are also responsible for the various animal diseases e.g., pleuropneumonia, bovine mastitis.
Plicate - Refers to any structure which is arranged in or having folds as the armed palisade of many gymnosperms and certain angiosperms.
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Pliocene - A geological period which is a subdivision of the Tertiary. It lasted approximately from 15 until 1 million years ago.
Plimorphic (pleomorphic, pleimorphic). Including organisms that are being formed in two or more different forms in their life cylc1e as many ascomycete fungi in two conidial states.
Plumule. Refers to the shoot portion of angiospermic embryos in seed and it is derived from epicotyl and is situated between co1yledons in dicotyledonous plants.
Plurilocular Sporangium - A sporangium having many locu1es e.g;., on sporophytic plants of brown alga. Ectocarpus. Compare tm-ilocu1ar sporangium
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Pneumathode - Refers to an outlet of the ventilating system of a plant, it usually has some loosely packed cells on the surface of the plant; through it exchange of gases is facilitated.
Pneumathophore - A specialized root growing vertically upwards into the air from roots embedded in the mud, and, being of loose construction makes gaseous exchange possible for the submerged roots.
Pneumotaxis - (1) Said of the response of reaction of an organism to the stimulus of carbon dioxide in solution.
(2) The response to the stimulus of gases in general.
Pod - A dry fruit which is produced from a single carpel. It is having a single loculus containing 1 (rarely) to many seeds, and usually opening at maturity by splitting along both ventral and dorsal sutures.
Podetium - Refers to an upright secondary thallus of lichens. It is stalk-like, cup-shaped, or much branched.
Podsol, Podzol - A type of soil profile which is developed under good drainage, relatively cool climate, and high rainfall.; These conditions lead to leaching so that this soil is typified by having a layer of humus on top, below which is a greyish, leached zone, below which is a darker layer where the leached salts get accumulated.
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Polarity - Refers to the condition resulting from the establishment of definite orientation during differentiation as in a cell, tissue or organ. It is important in early growth of plants as is revealed by separate development of root and shoot systems from initially formed bipolar embryo.
Polar Nuclei - Two nuclei in the embryo-sac which unite to give the polar fusion nucleus.
Pollarding - Refers to a form of severe pruning in which all the younger branches of a tree are cutr back virtually to the trunk.
Pollen - The micros pores of Gymnosperms and Angiosperms.
Pollen Chamber - The cavity which is formed in the apex of the nucellus of Gymnosperms, in which pollen grains lodge after pollination has occurred. The pollen grains slowly develop there and untimately bring about fertilization.
Pollen Mother Cell (PMC) - Describing a somatic cell in the pollen sac of gymnosperms or angiosperms which, after ; meiosis, produces a tetrad of pollens.
Pollen Sac - A cavity in an anther where the pollen is formed.
Pollen Tube - A tube which is formed on germination of a pollen grain that carries male gameted to the egg, and one to the central fusion nucleus with which it fuses to form the endosperm nucleus from which arises the endosperm.
Pollinarium - Refers to the aggregation of several pollen sacs which are transported as a single pollination unit.
Pollination - Refers to the transfer of pollens from male reproductive organ to female reproductive organ in flowering plants by involving some physical agency like wind, water or air or some biological agency like birds, insects, animals etc. If pollens of a plant reach the female organ of the same plant, it is called selfpollination and if pollens of one plant reach the female organ of some other plant of same species, it is called cross pollination
pollination Drop - Said of a drop of sugary fluid which is secreted through the micropyle is gymnosperms. It helps to traps pollens and then the pollen is drawn inside through micropyle to the ovule as the drop is reabsorbed.
pollinium - A mass of pollen grains which are held together by a sticky substance, arid transported as a whole during pollination.
Pollution Carpet - In stagnant and polluted water, a slimy layer is present on the bottom. It consists mainly of bacteria, detritus feeding protozoa, and fungi.
Polyadelphous - Used for an androecium when several of the ;;; stamens are joined by their filaments to form several bundles.
Polyandry - (1) Having a large and indefinite number of stamens.
(2) Of oospores formed when more than one functional antheridium is present.
Polyarch - Used for a stele which has many ;protoxylem stands.
Polyascus - Having many asci, especially when they are in one hymenium and not separated by sterile bands.
Polycarpellary - Consisting of many carpels.
Polycarpic - Able to fruit many times in succession.
Polycarpous - Having a gynoecium which is made up of several free carpels:
Polycentric - (1). Having many centres of growth and development, and more than One reproductive organ.;;;;;;; .
(2) Of a chromosome or chromatid which has several centromeres.
Polycephalous - Many headed.
Polychasium - A cymose inflorescence in which the branches and arising in groups ;of 3 or more at each node.
Polychlamydeous Chimaera - A periclinal chimaera in which the skin is more than two layers of cells thick.
Polycyclic Stele - Refers to the stele in which vascular bundles or meristeles are arranged in concentric rings as in some ferns.
Polymbryony - Refers to the condition of formation of more than one embryo in one ovule which may undergo development by division of one fertilized zygote (cleavage polyembryony) or may undergo development asexually from somatic tissue along with sexual embryo (adventive embryony).
Polygenes - Refer to many nonallelic genes all of which influence the same character with approximately additive effects. Such polygenic systems are also termed as polymeric systems.
Polymorplrism - (1) The occurrence in the same habitat of 2 or more distinct forms of a species in such proportions that the rarest cannot be supposed to be maintained by recurrent mutation from any other.
(2) Of a fungus having more than one spore-form.
Polynucleotide - A unit which is made up of several nucleotide units.
Polypeptide - Refers to a peptide chain which is made up of a large number of amino acid residues. Most of the polypeptides are having molecular weight of more than 5000. Protein molecule is compo; of one or more polypeptides.
Polypetalous - Refers to the condition of corolla in which individual units (petals) have been freely inserted on the receptacle.
Polyphyletic - Refer to taxa which have been originated from two or more separate ancestral lines.
Polyploidy - Refers to the condition of an individual which possesses more than two sets of genomes in its nuclei. Polyploidy may occur as a result of many situations and polyploids may be autopolyploids or allopolyploids.
Polyribosome (polysome). Refers to a chain of ribosomes attached together by a single molecule of mRNA. These chains are either folded or coiled into complex configurations, often spiral. Ribosomes move along mRNA.
Polysaccharide - A condensation product of monosaccharides. They are insoluble in water. The general formula is (CnH2n-2On-1) where n = 4-6 and x may be several thousands.
Polysepalous - Refers to the condition of calyx where its units (sepals) are freely inserted on the receptacle. Compare gamosepalous.
Polysomy - Said of the condition of cell or organism which is having several additional copies of some particular chromosome.
Polytene Chromosome - A chromosome having multistranded DNA which is produced due to repeated replication of DNA without subsequent separation. This gives rise to the giant chromosomes e.g., salivary gland chromosome of larvae of dipteran insects like Drosophia. Such chromosomes fine use in cytological and genetical research.
Pome - Refers to a false fruit that is developing from syncarpous, inferior ovary in which succulent edible part of greatly enlarged, unshaped receptacle which encloses the real fruit at its core. Such fruits are typical of Rosaceae.
Population - ;(1) A number of the same species living in a definite area.
(2) Genetically, a mating group, limited for special consideration, either by environment or breeding.
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