Connective tissue is one of the four basic types of animal tissue, along with epithelial tissue, muscle tissue, nervous tissue. It develops from the mesoderm. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. In the central nervous system, the three outer membranes that envelop the brain and spinal cord are composed of connective tissue, they protect the body. All connective tissue consists of three main components: ground substance and cells. Not all authorities include blood or lymph as connective tissue because they lack the fiber component. All are immersed in the body water; the cells of connective tissue include fibroblasts, macrophages, mast cells and leucocytes. The term "connective tissue" was introduced in 1830 by Johannes Peter Müller; the tissue was recognized as a distinct class in the 18th century. Connective tissue can be broadly subdivided into connective tissue proper, special connective tissue. Connective tissue proper consists of loose connective tissue and dense connective tissue Loose and dense connective tissue are distinguished by the ratio of ground substance to fibrous tissue.
Loose connective tissue has much more ground substance and a relative lack of fibrous tissue, while the reverse is true of dense connective tissue. Dense regular connective tissue, found in structures such as tendons and ligaments, is characterized by collagen fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction. Dense irregular connective tissue provides strength in multiple directions by its dense bundles of fibers arranged in all directions. Special connective tissue consists of reticular connective tissue, adipose tissue, cartilage and blood. Other kinds of connective tissues include fibrous and lymphoid connective tissues. Fibroareolar tissue is a mix of fibrous and areolar tissue. New vascularised connective tissue that forms in the process of wound healing is termed granulation tissue. Fibroblasts are the cells responsible for the production of some CT. Type I collagen is present in many forms of connective tissue, makes up about 25% of the total protein content of the mammalian body.
Characteristics of CT: Cells are spread through an extracellular fluid. Ground substance - A clear and viscous fluid containing glycosaminoglycans and proteoglycans to fix the body water and the collagen fibers in the intercellular spaces. Ground substance slows the spread of pathogens. Fibers. Not all types of CT are fibrous. Examples of non-fibrous CT include adipose blood. Adipose tissue gives "mechanical cushioning" to the body, among other functions. Although there is no dense collagen network in adipose tissue, groups of adipose cells are kept together by collagen fibers and collagen sheets in order to keep fat tissue under compression in place; the matrix of blood is plasma. Both the ground substance and proteins create the matrix for CT. Connective tissues are derived from the mesenchyme. Types of fibers: Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved. Loose and dense irregular connective tissue, formed by fibroblasts and collagen fibers, have an important role in providing a medium for oxygen and nutrients to diffuse from capillaries to cells, carbon dioxide and waste substances to diffuse from cells back into circulation.
They allow organs to resist stretching and tearing forces. Dense regular connective tissue, which forms organized structures, is a major functional component of tendons and aponeuroses, is found in specialized organs such as the cornea. Elastic fibers, made from elastin and fibrillin provide resistance to stretch forces, they are found in the walls of large blood vessels and in certain ligaments in the ligamenta flava. In hematopoietic and lymphatic tissues, reticular fibers made by reticular cells provide the stroma—or structural support—for the parenchyma—or functional part—of the organ. Mesenchyme is a type of connective tissue found in developing organs of embryos, capable of differentiation into all types of mature connective tissue. Another type of undifferentiated connective tissue is mucous connective tissue, found inside the umbilical cord. Various types of specialized tissues and cells are classified under the spectrum of connective tissue, are as diverse as brown and white adipose tissue, blood and bone.
Cells of the immune system, such as macrophages, mast cells, plasma cells and eosinophils are found scattered in loose connective tissue, providing the ground for starting inflammatory and immune responses upon the detection of antigens. There are many types of connective tissue disorders, such as: Connective tissue neoplasms including sarcomas such as hemangiopericytoma and malignant peripheral nerve sheath tumor in nervous tissue. Congenital diseases include Ehlers-Danlos Syndrome. Myxomatous degeneration – a pathological weakening of connective tissue. Mixed connective tissue disease – a disease of the autoimmune system undifferentiated connective tissue disease. Systemic lupus erythematosus – a major autoimmune disease of connective tissue Scurvy, caused by a deficiency of vitamin C, necessary for the synthesis of collagen. For microscopic viewing, most of the connective tissue staining-techniques, colour tissue fibers in contrasting shades. Collagen may be differentially stained by any of the following: Van Gieson's stain Masson's trichrome stain Mallory's t
Osmoregulation is the passive regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis; the higher the osmotic pressure of a solution, the more water tends to move into it. Pressure must be exerted on the hypertonic side of a selectively permeable membrane to prevent diffusion of water by osmosis from the side containing pure water. Organisms in aquatic and terrestrial environments must maintain the right concentration of solutes and amount of water in their body fluids. Two major types of osmoregulation are osmoregulators. Osmoconformers match their body osmolarity to their environment or passively. Most marine invertebrates are osmoconformers, although their ionic composition may be different from that of seawater. Osmoregulators regulate their body osmolarity, maintaining constant internal conditions.
They are more common in the animal kingdom. Osmoregulators control salt concentrations despite the salt concentrations in the environment. An example is freshwater fish; the gills uptake salt from the environment by the use of mitochondria-rich cells. Water will diffuse into the fish, so it excretes a hypotonic urine to expel all the excess water. A marine fish has an internal osmotic concentration lower than that of the surrounding seawater, so it tends to lose water and gain salt, it excretes salt out from the gills. Most fish are stenohaline, which means they are restricted to either salt or fresh water and cannot survive in water with a different salt concentration than they are adapted to. However, some fish show a tremendous ability to osmoregulate across a broad range of salinities. Flounder have been observed to inhabit two utterly disparate environments—marine and fresh water—and it is inherent to adapt to both by bringing in behavioral and physiological modifications; some marine fish, like sharks, have adopted a different, efficient mechanism to conserve water, i.e. osmoregulation.
They retain urea in their blood in higher concentration. Urea damages living tissues so, to cope with this problem, some fish retain trimethylamine oxide; this provides a better solution to urea's toxicity. Sharks, having higher solute concentration, do not drink water like fresh water fish. While there are no specific osmoregulatory organs in higher plants, the stomata are important in regulating water loss through evapotranspiration, on the cellular level the vacuole is crucial in regulating the concentration of solutes in the cytoplasm. Strong winds, low humidity and high temperatures all increase evapotranspiration from leaves. Abscisic acid is an important hormone in helping plants to conserve water—it causes stomata to close and stimulates root growth so that more water can be absorbed. Plants share with animals the problems of obtaining water but, unlike in animals, the loss of water in plants is crucial to create a driving force to move nutrients from the soil to tissues. Certain plants have evolved methods of water conservation.
Xerophytes are plants that can survive in dry habitats, such as deserts, are able to withstand prolonged periods of water shortage. Succulent plants such as the cacti store water in the vacuoles of large parenchyma tissues. Other plants have leaf modifications to reduce water loss, such as needle-shaped leaves, sunken stomata, thick, waxy cuticles as in the pine; the sand-dune marram grass has rolled leaves with stomata on the inner surface. Hydrophytes are plants in water habitats, they grow in water or in wet or damp places. In these plants the water absorption occur through the whole surface of the plant, e.g. the water lily. Halophytes are plants living in marshy areas, they have to absorb water from such a soil which has higher salt concentration and therefore lower water potential. Halophytes cope with this situation by activating salts in their roots; as a consequence, the cells of the roots develop lower water potential which brings in water by osmosis. The excess salt can be excreted out from salt glands on leaves.
The salt thus secreted by some species help them to trap water vapours from the air, absorbed in liquid by leaf cells. Therefore, this is another way of obtaining additional water from air, e.g. glasswort and cord-grass. Mesophytes are plants living in lands of temperate zone, they can compensate the water lost by transpiration through absorbing water from the soil. To prevent excessive transpiration they have developed a waterproof external covering called cuticle. Kidneys play a large role in human osmoregulation by regulating the amount of water reabsorbed from glomerular filtrate in kidney tubules, controlled by hormones such as antidiuretic hormone and angiotensin II. For example, a decrease in water potential is detected by osmoreceptors in the hypothalamus, which stimulates ADH release from the pituitary gland to increase the permeability of the walls of the collecting ducts in the kidneys. Therefore, a large proportion of water is reabsorbed from fluid in the kidneys to prevent t
Fresh water is any occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, icebergs, ponds, rivers and underground water called groundwater. Fresh water is characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water is not the same as potable water. Much of the earth's fresh water is unsuitable for drinking without some treatment. Fresh water can become polluted by human activities or due to occurring processes, such as erosion. Water is critical to the survival of all living organisms; some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live. Fresh water can be defined as water with less than 500 parts per million of dissolved salts. Other sources give higher upper salinity limits for e.g. 1000 ppm or 3000 ppm. Fresh water habitats are classified as either lentic systems, which are the stillwaters including ponds, lakes and mires.
There is, in addition, a zone which bridges between groundwater and lotic systems, the hyporheic zone, which underlies many larger rivers and can contain more water than is seen in the open channel. It may be in direct contact with the underlying underground water; the majority of fresh water on Earth is in ice caps. The source of all fresh water is precipitation from the atmosphere, in the form of mist and snow. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled. In industrialized areas rain is acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of rivers. In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds.
This can give rise to elevated concentrations of sodium, chloride and sulfate as well as many other compounds in smaller concentrations. In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa. Saline water in oceans and saline groundwater make up about 97% of all the water on Earth. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers and snow, 0.5–0.75% as fresh groundwater and soil moisture, less than 0.01% of it as surface water in lakes and rivers. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the African Great Lakes, 22% in Lake Baikal in Russia, 21% in the North American Great Lakes, 14% in other lakes.
Swamps have most of the balance with only a small amount in rivers, most notably the Amazon River. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in ice sheets. Many areas suffer from lack of distribution such as deserts. Water is a critical issue for the survival of all living organisms; some can use salt water but many organisms including the great majority of higher plants and most mammals must have access to fresh water to live. Some terrestrial mammals desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, they have mechanisms to conserve water to the maximum degree. Fresh water creates a hypotonic environment for aquatic organisms; this is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted.
Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh water and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; the eel uses the hormone prolactin, while in salmon the hormone cortisol plays a key role during this process. Many sea birds have special glands at the base of the bill; the marine iguanas on the Galápagos Islands excrete excess salt through a nasal gland and they sneeze out a salty excretion. Freshwater molluscs include freshwater snails and freshwater bivalves. Freshwater crustaceans include crayfish. Freshwater biodiversity faces many threats; the World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014.
These declines continue to outpace
Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance, i.e. external morphology, as well as the form and structure of the internal parts like bones and organs, i.e. internal morphology. This is in contrast to physiology, which deals with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts; the word "morphology" is from the Ancient Greek μορφή, morphé, meaning "form", λόγος, lógos, meaning "word, research". While the concept of form in biology, opposed to function, dates back to Aristotle, the field of morphology was developed by Johann Wolfgang von Goethe and independently by the German anatomist and physiologist Karl Friedrich Burdach. Among other important theorists of morphology are Lorenz Oken, Georges Cuvier, Étienne Geoffroy Saint-Hilaire, Richard Owen, Karl Gegenbaur and Ernst Haeckel.
In 1830, Cuvier and E. G. Saint-Hilaire engaged in a famous debate, said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or evolution. Comparative morphology is analysis of the patterns of the locus of structures within the body plan of an organism, forms the basis of taxonomical categorization. Functional morphology is the study of the relationship between the structure and function of morphological features. Experimental morphology is the study of the effects of external factors upon the morphology of organisms under experimental conditions, such as the effect of genetic mutation. "Anatomy" is a "branch of morphology that deals with the structure of organisms". Molecular Morphology is a term used in English-speaking countries for describing the structure of compound molecules, such as polymers and ribonucleic acid. Gross Morphology refers to the collective structures of an organism as a whole as a general description of the form and structure of an organism, taking into account all of its structures without specifying an individual structure.
Most taxa differ morphologically from other taxa. Related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look similar, or even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire a similar appearance as a result of convergent evolution or mimicry. In addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are smaller than workers. A further problem with relying on morphological data is that what may appear, morphologically speaking, to be two distinct species, may in fact be shown by DNA analysis to be a single species; the significance of these differences can be examined through the use of allometric engineering in which one or both species are manipulated to phenocopy the other species. A step relevant to the evaluation of morphology between traits/features within species, includes an assessment of the terms: homology and homoplasy.
Homology between features indicate. Alternatively, homoplasy between features describes those that can resemble each other, but derive independently via parallel or convergent evolution. Invention and development of microscopy enable the observation of 3-D cell morphology with both high spatial and temporal resolution; the dynamic processes of these cell morphology which are controlled by a complex system play an important role in varied important biological process, such as immune and invasive responses. Comparative anatomy Insect morphology Morphometrics Neuromorphology Phenetics Phenotype Phenotypic plasticity Plant morphology Media related to Morphology at Wikimedia Commons
Ilya Ilyich Mechnikov was a Russian zoologist best known for his pioneering research in immunology. In particular, he is credited with the discovery of phagocytes in 1882; this discovery turned out to be the major defence mechanism in innate immunity. He and Paul Ehrlich were jointly awarded the 1908 Nobel Prize in Physiology or Medicine "in recognition of their work on immunity", he is credited by some sources with coining the term gerontology in 1903, for the emerging study of aging and longevity. He established the concept of cell-mediated immunity, while Ehrlich established the concept of humoral immunity, their works are regarded as the foundation of the science of immunology. In immunology, he is given an epithet the "father of natural immunity". Mechnikov was born in Kharkov Governorate, now Dvorichna Raion, Ukraine, he was the youngest of five children of Ilya Ivanovich Mechnikov, a Russian officer of the Imperial Guard. His mother, Emilia Lvovna, the daughter of the Jewish writer Leo Nevakhovich influenced him on his education in science.
The family name Mechnikov is a translation from Romanian, since his father was a descendant of the Chancellor Yuri Stefanovich, the grandson of Nicolae Milescu. The word "mech" is a Russian translation of the Romanian "spadă", his elder brother Lev became a prominent sociologist. He entered Kharkiv Lycée in 1856. Convinced by his mother to study natural sciences instead of medicine, in 1862 he tried to study biology at the University of Würzburg, but the German academic session would not start by the end of the year. So he enrolled at Kharkiv University for natural sciences, completing his four-year degree in two years. In 1864 he went to Germany to study marine fauna on the small North Sea island of Heligoland, he was advised by the botanist Ferdinand Cohn to work with Rudolf Leuckart at the University of Giessen. It was in Leuckart’s laboratory that he made his first scientific discovery of alternation of generations in nematodes and at Munich Academy. In 1865, while at Giessen, he discovered intracellular digestion in flatworm, this study influenced his works.
Moving to Naples the next year he worked on a doctoral thesis on the embryonic development of the cuttle-fish Sepiola and the crustacean Nebalia. A cholera epidemic in the autumn of 1865 made him move to the University of Göttingen, where he worked with W. M. Keferstein and Jakob Henle. In 1867 he returned to Russia to get his doctorate with Alexander Kovalevsky from the University of St. Petersburg. Together they won the Karl Ernst von Baer prize for their theses on the development of germ layers in invertebrate embryos. Mechnikov was appointed docent at the newly established Imperial Novorossiya University. Only twenty-two years of age, he was younger than his students. After involving in a conflict with senior colleague over attending scientific meeting, in 1868 he transferred to the University of St. Petersburg, where he experienced a worse professional environment. In 1870 he returned to Odessa to take up the appointment of Titular Professor of Zoology and Comparative Anatomy. In 1882 he resigned from Odessa University due to political turmoils after the assassination of Alexander II.
He went to Messina to set up his private laboratory. He returned to Odessa as director of an institute set up to carry out Louis Pasteur's vaccine against rabies, but due to some difficulties left in 1888 and went to Paris to seek Pasteur's advice. Pasteur gave him an appointment at the Pasteur Institute, where he remained for the rest of his life. Mechnikov became interested in the study of microbes, the immune system. At Messina he discovered phagocytosis after experimenting on the larvae of starfish. In 1882 he first demonstrated the process when he pinned small thorns into starfish larvae, he found unusual cells surrounding the thorns; the thorns were from a tangerine tree made into a Christmas tree. He realized that in animals which have blood, the white blood cells gather at the site of inflammation, he hypothesised that this could be the process by which bacteria were attacked and killed by the white blood cells, he discussed his hypothesis with Carl Friedrich Wilhelm Claus, Professor of Zoology at the University of Vienna, who suggested to him the term "phagocyte" for a cell which can surround and kill pathogens.
He delivered his findings at Odessa University in 1883. His theory, that certain white blood cells could engulf and destroy harmful bodies such as bacteria, met with scepticism from leading specialists including Louis Pasteur and others. At the time, most bacteriologists believed that white blood cells ingested pathogens and spread them further through the body, his major supporter was Rudolf Virchow, who published his research in his Archiv für pathologische Anatomie und Physiologie und für klinische Medizin. His discovery of these phagocytes won him the Nobel Prize in 1908, he worked with Émile Roux on calomel in ointment form in an attempt to prevent people from contracting the sexually transmitted disease syphilis. In 1887, he observed that leukocytes isolated from the blood of various animals were attracted towards certain bacteria; the first studies of leukocyte killing in the presence of specific antiserum were performed by Joseph Denys and Joseph Leclef, followed by Leon Marchand and Mennes between 1895 and 1898.
Almoth E. Wright was the first to quantify this phenomenon and advocated its potential therapeutic importance; the s
The paraphyletic "Platyzoa" are a group of protostome unsegmented animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the phylum Platyhelminthes, a new phylum, the Acanthognatha, into which he gathered several described phyla of microscopic animals. More it has been described as paraphyletic, containing the Rouphozoa and the Gnathifera. One scheme placed the following phyla in Platyzoa: RouphozoaPlatyhelminthes Gastrotricha GnathiferaSyndermata Rotifera Seisonida Acanthocephala Gnathostomulida Micrognathozoa Cycliophora None of the Platyzoa groups have a respiration or circulation system because of their small size, flat body or parasitic lifestyle; the Platyhelminthes and Gastrotricha are acoelomate. The other phyla have a pseudocoel, share characteristics such as the structure of their jaws and pharynx, although these have been secondarily lost in the parasitic Acanthocephala, they form. The name "Platyzoa" is used; the Platyzoa are close relatives of the Lophotrochozoa.
Together the two make up the Spiralia. Syndermata was a proposed clade that included Acanthocephala and rotifers, but as it appears they are not sister groups after all, the clade has been abandoned. A recent possible cladogram is shown which would show that the Lophotrochozoa emerged within Platyzoa as a sister group of the Rouphozoa; the Lophotrochozoa and Rouphozoa are named the Platytrochozoa. This makes the Platyzoa a paraphyletic group; the Taxonomicon - Taxon: Infrakingdom Platyzoa Cavalier-Smith, 1998 - retrieved January 31, 2006 Triploblastic Relationships with Emphasis on the Acoelomates and the Position of Gnathostomulida, Cycliophora and Chaetognatha: A Combined Approach of 18S rDNA Sequences and Morphology - retrieved January 31, 2006 Myzostomida Are Not Annelids: Molecular and Morphological Support for a Clade of Animals with Anterior Sperm Flagella - retrieved January 31, 2006 Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion?
- retrieved January 31, 2006
Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants parthenogenesis is a component process of apomixis. Parthenogenesis occurs in some plants, some invertebrate animal species and a few vertebrates; this type of reproduction has been induced artificially in a few species including fish and amphibians. Normal egg cells form after meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, are non-viable, parthenogenetic offspring have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles; the offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are formed without meiosis.
If meiosis occurs, the offspring will get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation. Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes or two W chromosomes, or they could have one Z and one W chromosome; some species reproduce by parthenogenesis, while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis; the switch between sexuality and parthenogenesis in such species may be triggered by the season, or by a lack of males or by conditions that favour rapid population growth. In these species asexual reproduction occurs either in summer or as long as conditions are favourable; this is because in asexual reproduction a successful genotype can spread without being modified by sex or wasting resources on male offspring who won't give birth.
In times of stress, offspring produced by sexual reproduction may be fitter as they have new beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions. Many taxa with heterogony have within them species that have lost the sexual phase and are now asexual. Many other cases of obligate parthenogenesis are found among polyploids and hybrids where the chromosomes cannot pair for meiosis; the production of female offspring by parthenogenesis is referred to as thelytoky while the production of males by parthenogenesis is referred to as arrhenotoky. When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky. Parthenogenesis can occur without meiosis through mitotic oogenesis; this is called apomictic parthenogenesis. Mature egg cells are produced by mitotic divisions, these cells directly develop into embryos.
In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother. Examples include aphids. Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid. In other cases, collectively called automictic parthenogenesis, the ploidy is restored to diploidy by various means; this is. In automictic parthenogenesis, the offspring differ from their mother, they are called half clones of their mother. Automixis is a term. Diploidy might be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed; this is referred to as an endomitotic cycle. This may happen by the fusion of the first two blastomeres. Other species restore their ploidy by the fusion of the meiotic products; the chromosomes may not separate at one of the two anaphases or the nuclei produced may fuse or one of the polar bodies may fuse with the egg cell at some stage during its maturation.
Some authors consider all forms of automixis sexual. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined together; the criterion for "sexuality" varies from all cases of restitutional meiosis, to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences; the genetic composition of the offspring depends on. When endomitosis occurs before meiosis or when central fusion occurs, the offspring get all to mor