Cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. It is part of developmental biology. Different tissues have different kinds of organelles inside the cells.
Differentiation occurs many times during the development of a multicellular organism. The organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is also a common process in adults: adult stem cells divide to make fully-differentiated daughter cells during tissue repair and during normal cell turnover.
Differentiation dramatically changes a cell's size, shape, metabolic activity, and responsiveness to signals. These changes are largely due to changes in gene expression. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself. It does involve switching off many genes not needed in a particular tissue. Thus, cells in different tissues may have very different physical characteristics despite having the same genome.
"Cell potency" is a cell's ability to differentiate into other cell types. A cell that is able to differentiate into many cell types is known as "pluripotent". Such cells are called stem cells in animals and meristematic cells in higher plants. A cell that is able to differentiate into all cell types is known as "totipotent". In mammals, only the zygote and early embryonic cells are totipotent, while in plants many differentiated cells can become totipotent with simple laboratory techniques.
Morphogenesis
Morphogenesis (meaning the "beginning of shape"), is the biological process that causes an organism to develop its shape.
It is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation.
The process controls the organized spatial distribution of cells during the embryonic development of an organism. Morphogenetic responses may be induced in organisms by hormones, by substances produced by other organisms, or by mechanical stresses induced by spatial patterning of the cells. Morphogenesis can take place in an embyro, a mature organism, in cell culture or inside tumor cell masses.
Gastrulation
Gastrulation is a phase early in the development of most animal embryos. In it the embryo is dramatically restructured by cell migration.
Gastrulation varies in different phyla. It is followed by "organogenesis", when individual organs develop within the newly formed "germ layers".
The gastrula is the double-walled stage of the embryo. During gastrulation, some of the cells of the blastula migrate inwards to make an inner layer, the "endoderm". In some animals another cell layer forms, the "mesoderm", between the endoderm and the "ectoderm".
Among animals, sponges show the simplest organization, having a single germ layer. Cnidaria and ctenophores show an increase in complexity, having two germ layers, the "endoderm" and "ectoderm". All higher animals (from flatworms to humans) possess a "mesoderm" as well as ectoderm and endoderm.
The purpose of gastrulation is to position the 3 embryonic germ layers, the endoderm, ectoderm and mesoderm. These layers later develop into certain bodily systems.
Wat Phra-sri Rattana Mahathat
Wat Phra-sri Rattana Mahathat or Wat Yai is the most important monastery of Phitsanulok. It was built in the reign of Phra Maha Thamma Racha I in 1357 BCE. In the temple, there is a Buddha image called Phra Buddha Chinnaraj. The pearl inlaid wooden doors of the temple were built by King Borommakot in 1756 as tribute to Phra Buddha Chinnaraj. Behind the temple, there is a large pagoda high with a staircase leading up to the niche containing the Buddha relics. In front of the pagoda, there is Phra Attharos, a standing Buddha image.
Jikji
Jikji is the oldest extant movable metal type book in the world.
"Jikji" is the short title of a Korean book whose full title can be translated as "Anthology of the Great Priests' Zen Teachings". It is a Buddhist document, and was printed during Korea's Goryeo era in 1377.
"Jikji" is a book about Zen Buddhism published in Heungdeok temple. It was written by the Buddhist monk Baegun who died three years before this edition was printed. Baegun was the chief priest of the Anguk and Shingwang temples in Haeju.
"Jikji" was published 78 years before Johannes Gutenberg's "42-Line Bible". "Jikji" consists of two volumes. Only the second volume is extant. This volume is held in the National Library of France. UNESCO confirmed "Jikji" as the world's oldest metalloid type book in September 2001, and includes it in the "Memory of the World" program.
Bibliothèque nationale de France
The Bibliothèque nationale de France is the National Library of France in Paris.
The National Library of France was founded at the Louvre by Charles V in 1368. It grew under Louis XIV and opened to the public in 1692.
Following a series of regime changes in France, it became the Imperial National Library and in 1868 it moved to new buildings on the Rue de Richelieu. In 1896, the library was the largest collection of books in the world.
In 1988, President François Mitterrand agreed to build a new modern library. It now contains more than twenty million volumes.
The library has 5,000 Greek manuscripts and the Jikji (the oldest printed document with movable type).
Fitness
Fitness in biology is the relative ability of an organism to survive and pass on its genes to the next generation. It is a central idea in evolutionary theory. Fitness is usually equal to the proportion of the individual's genes in all the genes of the next generation.
Like all terms in evolutionary biology, fitness is defined in terms of an interbreeding population, which might or might not be a whole species. If differences in individual genotypes affect fitness, then the frequencies of the genotypes will change over generations; the genotypes with higher fitness become more common. This is the process called natural selection.
An individual's fitness is caused by its phenotype, and passed on by its genotype. The fitnesses of different individuals with the same genotype are not necessarily equal. It depends on the environment in which the individuals live, and on accidental events. However, since the fitness of the genotype is an averaged quantity, it reflects the reproductive outcomes of "all" individuals with that genotype.
Fitness measures the number of the "copies" of the genes of an individual in the next generation. It doesn't really matter how the genes arrive in the next generation. For an individual, it is equally "beneficial" to reproduce itself, or to help relatives with similar genes to reproduce, "as long as similar number of copies of individual's genes get passed on to the next generation". Selection which promotes this kind of helper behaviour is called kin selection.
Our closest relatives (parents, siblings, and our own children) share on average 50% (half) of our genes. One step further removed are grandparents. With each of them we share on average 25% (a quarter) of our genes. That is a measure of our relatedness to them. Next come first cousins (children of our parents' siblings). We share 12.5% (1/8) of their genes.
William Hamilton added various ideas to the notion of fitness. His rule suggests that a costly action should be performed if:
Fitness costs and benefits are measured in fecundity.
Inclusive fitness is a term which is essentially the same as fitness, but emphasises the group of genes rather than individuals.
Biological fitness says how well an organism can reproduce, and spread its genes to its offspring. The theory of inclusive fitness says that the fitness of an organism is also increased to the extent that its close relatives also reproduce. This is because relatives share genes in proportion to their relationship.