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In unitary populations, each individual is derived from zygote (the product of fertilization, of male and female gamete). They are mobile. The body of unitary organisms is a determinate, structure consisting usually of a strictly defined number of parts (such as legs or wings), established only during embryogenesis viz. all dogs have four legs, all squid have two eyes,, etc. Humans are perfect examples of unitary organisms. A life begins when a sperm fertilizes, an egg to form a zygote. This implant in the wall of the uterus and the complex processes, of embryonic development commence. By 6 weeks the fetus has a recognizable nose, eyes,, ears and limbs with digits and accidents apart, will remain in this form until it dies. The fetus, continues to grow until birth, and then the infant grows until perhaps the 18th year of life; but, the only changes in form (as opposed to size) are the relatively minor ones associated with, sexual maturity. The reproductive phase lasts for perhaps 30 years in females and rather longer, in males. This is followed by a phase of senescence. Death can intervene at any time, but for, surviving individuals the succession of phases is, like form, entirely predictable., , In modular populations, the zygote develops into a unit of construction (a module) that, then produces further, similar modules. Most plants are modular. A tree, shrub, or herbaceous, plant grown from a seed is an individual with its own genetic characteristics. Once established,, some species of trees, shrubs, and many perennial herbaceous plants grow root extensions to, send up new shoots or suckers that may remain attached to root extensions or break off to live, independently. These new modules (or clones) may cover a considerable area and appear to, be individuals. In modular organisms, neither timing nor form is predictable. Individuals are, composed of a highly variable number of such modules, and their program of development is, strongly dependent on their interaction with their environment. The product is almost always, branched, and except for a juvenile phase, effectively immobile. Some modular organisms such, as trees may grow vertically while others like grasses spread horizontally on the substratum., Modular organisms tend to be sessile or passively mobile and, as genetic individuals, have the, capacity for exponential increase in size. They do not necessarily undergo systemic senescence,, and do not segregate somatic from germ line cells., , Kays and Harper (1974) recognized the dichotomy in modular organisms and introduced, the terms genet and ramet to avoid confusion. Thus, individuals that are produced asexually, (e.g. ‘daughter’ plants of buttercups, bulbs, polyps of Obelia, corals) and have the potential for, growth independent of the parent are called ramets; and a population of ramets with the same, (‘maternal’) parentage constitutes a clone. A genet, on the other hand, is an organism, however, much ramified, which has arisen from a single zygote-all parts having the same genotype. The, ramets may remain physically linked to the parent genet or they may separate, functioning, independently. These modules can produce seeds and their own lateral extensions or ramets., Thus, by producing ramets, the genet can cover a relatively large area and considerably extend, its life. Some modules die, others live, and new ones appear., , Plants are the most obvious group of modular organisms. There are, however, many, important groups of modular animals also (including around 19 phyla of sponges, hydroids,, corals, bryozoans and colonial ascidians), and many modular protists and fungi. Technically, to, , Scanned with CamScanner

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coe cares, study populations of modular organisms, we must recognize two levels of population Structure:, , the module (ramet) and the individual (genet). For practical purposes, however, ramets ate, often counted as and function as individual members of the population., , Scanned with CamScanner