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ABC model of flower development guided by three groups of homeotic genes.. The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower.
The duplicated genes may attain new function, either by changes in expression pattern or changes in activity. Polyploidy and gene duplication are believed to be among the most powerful forces in evolution of plant form. It is not known though, why genome doubling is such a frequent process in plants.
Flowers emerged in plant evolution as an adaptation for the promotion of cross-fertilisation (outcrossing), a process that allows the masking of deleterious mutations in the genome of progeny. The genetic masking effect of cross-fertilisation sexual reproduction is known as genetic complementation . [ 23 ]
Empowerment is a key concept in the discourse on promoting civic engagement. Empowerment as a concept, which is characterized by a move away from a deficit-oriented towards a more strength-oriented perception, can increasingly be found in management concepts, as well as in the areas of continuing education and self-help. [citation needed]
While all organisms vary from individual to individual, plants exhibit an additional type of variation. Within a single individual, parts are repeated which may differ in form and structure from other similar parts. This variation is most easily seen in the leaves of a plant, though other organs such as stems and flowers may show similar variation.
Germination is the early growth of a plant from a seed. Meanwhile, dormancy precedes germination and serves to preserve a seed until conditions are receptive towards growth. The transition from dormancy to germination seems to depend on the removal of factors inhibiting growth. There are many models for germination which may differ between species.
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The process of androgenesis allows a mature plant embryo to form from a reduced, or immature, pollen grain. [20] Androgenesis usually occurs under stressful conditions. [20] Embryos that result from this mechanism can germinate into fully functional plants. As mentioned, the embryo results from a single pollen grain.