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110-504: An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote ) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the animal hatches. Most arthropods , vertebrates (excluding live-bearing mammals ), and mollusks lay eggs, although some, such as scorpions , do not. Reptile eggs, bird eggs , and monotreme eggs are laid out of water and are surrounded by
220-416: A nutrient -rich tissue , inside the seed . The two central-cell maternal nuclei (polar nuclei) that contribute to the endosperm arise by mitosis from the single meiotic product that also gave rise to the egg. Therefore, maternal contribution to the genetic constitution of the triploid endosperm is double that of the embryo. One primitive species of flowering plant, Nuphar polysepala , has endosperm that
330-431: A zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination , which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction . During double fertilisation in angiosperms ,
440-405: A dry period, these frogs tuck their ventral areas under them so that only their resistant skin is exposed. They also secrete a water-resistant mucus to seal any small gaps when they aestivate . If disturbed and forced to move, they lose a significant amount of water and may not be able to survive the rest of the dry season. They are also able to lose up to sixty percent of their body weight over
550-407: A few days after; therefore, in most mammals, it is more common for ejaculation to precede ovulation than vice versa. When sperm are deposited into the anterior vagina, they are not capable of fertilisation (i.e., non-capacitated) and are characterised by slow linear motility patterns. This motility, combined with muscular contractions enables sperm transport towards the uterus and oviducts . There
660-541: A green or blue ground colour, while protoporphyrin IX produces reds and browns as a ground colour or as spotting. Non-passerines typically have white eggs, except in some ground-nesting groups such as the Charadriiformes , sandgrouse and nightjars , where camouflage is necessary, and some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay coloured eggs, even if there
770-434: A longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails . Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys , coelacanth and
880-420: A more violent and rapid non-linear motility pattern as sperm approach the oocyte. The capacitated spermatozoon and the oocyte meet and interact in the ampulla of the fallopian tube . Rheotaxis, thermotaxis and chemotaxis are known mechanisms that guide sperm towards the egg during the final stage of sperm migration. Spermatozoa respond (see Sperm thermotaxis ) to the temperature gradient of ~2 °C between
990-402: A naked egg cell. Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole ), with the cell nucleus and most of the cytoplasm in the other (the animal pole ). The cell cleavage is uneven, and mainly concentrated in the cytoplasma-rich animal pole. The larger yolk content of the mesolecithal eggs allows for
1100-426: A nitrogenous end product. Anywhere between fifty and seventy-five percent of total waste nitrogen is converted into uric acid, while the remaining amount is expelled as urea in waste. This uric acid excreted can be released in a solid form and does not result in any net water loss for the frog. This is especially relevant for grey foam-nest tree frogs as they primarily inhabit dry environments, where minimizing water loss
1210-414: A protective shell , either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to crack, pip, or break the eggshell or covering. The largest recorded egg is from a whale shark and
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#17327656353341320-540: A result of polyandry are more likely to survive than offspring of monogamous matings. Egg deposition primarily occurs in still, fresh water in order to keep the eggs moist during development. A typical clutch size can be anywhere between 500 and 1250 eggs. Grey foam-nest tree frogs strategically hang their foam nests on branches of trees above water at differing heights. Polyandry can positively impact fertilization success and offspring production in grey-foam nest tree frogs. This might be because more male mates ensures that
1430-569: A right angle to their inner two fingers on each hand. The grey foam-nest tree frog typically has a snout length of 50–80 mm. Males have a snout-vent length of 43–75 mm, while females have a 60–90 mm snout-vent length. They have relatively impermeable skin, which allows them to survive dry spells under tree detritus. Their skin is slightly bumpy and dry. Their coloration ranges between white and brown and changes in response to temperature (see adaptations below). They tend to turn white when they die. The grey foam-nest tree frog typically has
1540-523: A shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina . Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors ) to about 17 (the grey partridge ). Some birds lay eggs even when not fertilized (e.g. hens ); it
1650-517: A short period lasting some days; a queen may mate with eight or more drones . She then stores the sperm for the rest of her life, perhaps for five years or more. In many fungi (except chytrids ), as in some protists, fertilisation is a two step process. First, the cytoplasms of the two gamete cells fuse (called plasmogamy ), producing a dikaryotic or heterokaryotic cell with multiple nuclei. This cell may then divide to produce dikaryotic or heterokaryotic hyphae . The second step of fertilisation
1760-498: A snout length of 50–80 mm. Males have a snout-vent length of 43–75 mm, while females have a 60–90 mm snout-vent length. Grey foam-nest tree frogs usually reside in varying habitats, such as savannah, shrubland, forests, pastureland, and urban areas. There have been mentions of these frogs living in Australia in addition to their native range in southern Africa. They are considered habitat specialists, which refers to
1870-945: A species known to only breed in unsettled environments and unperturbed areas. Grey foam-nest tree frogs dislike arid conditions and need humidity to survive; however, they can still be found in dry environments such as: dry forests, miombo, mopane, savannah, and cultivated areas in low altitudes. They are able to survive dry seasons under loose bark, hence why they are referred to as tree frogs. Large rainstorms stimulate an increase in breeding from these frogs, because high humidity decreases egg mortality and improves survival across multiple stages of life. Habitat destruction and disturbance impacts breeding abilities of these frogs. Mating activity of grey foam-nest tree frogs typically occurs at night from October to February in south-eastern Africa's wet summer months. These frogs choose to mate in arboreal settings, as they create their foam nests in tree branches overhanging bodies of water. Female mate choice
1980-567: A subject of semantic arguments about the beginning of pregnancy , typically in the context of the abortion debate. Upon gastrulation , which occurs around 16 days after fertilisation, the implanted blastocyst develops three germ layers, the endoderm, the ectoderm and the mesoderm, and the genetic code of the father becomes fully involved in the development of the embryo; later twinning is impossible. Additionally, interspecies hybrids survive only until gastrulation and cannot further develop. However, some human developmental biology literature refers to
2090-525: A sugar free pollen germination medium and a medium with purified TTS proteins both grew. However, in the TTS medium, the tubes grew at a rate 3x that of the sugar-free medium. TTS proteins were also placed on various locations of semi in vivo pollinated pistils, and pollen tubes were observed to immediately extend toward the proteins. Transgenic plants lacking the ability to produce TTS proteins had slower pollen tube growth and reduced fertility. The rupture of
2200-478: A thick layer of extracellular matrix that surrounds the egg and is similar to the role of the vitelline membrane in sea urchins, binds the sperm. Unlike sea urchins, the sperm binds to the egg before the acrosomal reaction. ZP3 , a glycoprotein in the zona pellucida, is responsible for egg/sperm adhesion in humans. The receptor galactosyltransferase (GalT) binds to the N-acetylglucosamine residues on
2310-400: A thin spike at the head of the sperm called the acrosomal process . The sperm binds to the egg through another ligand reaction between receptors on the vitelline membrane . The sperm surface protein bindin, binds to a receptor on the vitelline membrane identified as EBR1. Fusion of the plasma membranes of the sperm and egg are likely mediated by bindin. At the site of contact, fusion causes
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#17327656353342420-453: A time away from water. These include uricotelism , rectal water reabsorption, skin resistant to desiccation, and skin that changes color in response to temperature. They have relatively impermeable skin, which allows them to survive dry spells under tree detritus. They are also able to lose up to sixty percent of their body weight over the course of several months. The grey foam-nest tree frog forms uric acid and excretes it from their body as
2530-504: A variety of unique habitats. They typically choose environments hanging over bodies of water, but if this is not possible, they lay eggs on any other suitable objects. Occasionally, they lay eggs directly in water or grassy vegetation above water. These tree frogs are more likely to choose lightly wooded savannas and forested areas because these environments have sufficient resources to support adult frogs. Foam-nest building behaviors and patterns have evolved several times. The foam nest made by
2640-448: Is karyogamy , the fusion of the nuclei to form a diploid zygote. In chytrid fungi, fertilisation occurs in a single step with the fusion of gametes, as in animals and plants. There are three types of fertilisation processes in protozoa: Algae, like some land plants, undergo alternation of generations . Some algae are isomorphic, where both the sporophyte (2n) and gameteophyte (n) are the same morphologically. When algae reproduction
2750-448: Is a pH gradient within the micro-environment of the female reproductive tract such that the pH near the vaginal opening is lower (approximately 5) than the oviducts (approximately 8). The sperm-specific pH-sensitive calcium transport protein called CatSper increases the sperm cell permeability to calcium as it moves further into the reproductive tract. Intracellular calcium influx contributes to sperm capacitation and hyperactivation, causing
2860-664: Is a species of frog in the family Rhacophoridae . They are found in southern Africa. Its natural habitats are subtropical or tropical dry forest, dry savanna, moist savanna, subtropical or tropical dry shrubland, subtropical or tropical moist shrubland, subtropical or tropical dry lowland grassland, subtropical or tropical seasonally wet or flooded lowland grassland, intermittent freshwater marshes, arable land, pastureland, rural gardens, urban areas, heavily degraded former forests, ponds, and canals and ditches. Grey foam-nest tree frogs are known for simultaneous polyandry, where female frogs have multiple mates on separate territories that guard
2970-610: Is also estimated that about 42% of flowering plants exhibit a mixed mating system in nature. In the most common kind of mixed mating system, individual plants produce a single type of flower and fruits may contain self-fertilised, outcrossed or a mixture of progeny types. The transition from cross-fertilisation to self-fertilisation is the most common evolutionary transition in plants, and has occurred repeatedly in many independent lineages. About 10-15% of flowering plants are predominantly self-fertilising. Under circumstances where pollinators or mates are rare, self-fertilisation offers
3080-402: Is described as oogamous, the male and female gametes are different morphologically, where there is a large non-motile egg for female gametes, and the male gamete are uniflagellate (motile). Via the process of syngamy, these will form a new zygote, regenerating the sporophyte generation again. Meiosis results in a random segregation of the genes that each parent contributes. Each parent organism
3190-405: Is diploid, resulting from the fusion of a sperm with one, rather than two, maternal nuclei. It is believed that early in the development of angiosperm lineages, there was a duplication in this mode of reproduction, producing seven-celled/eight-nucleate female gametophytes, and triploid endosperms with a 2:1 maternal to paternal genome ratio. In many plants, the development of the flesh of the fruit
3300-401: Is highly important. Individual frogs can change their color from chalky white to dark brown, with the brown coloration presenting in a geometric/bark pattern. These frogs change their skin colors in response to temperature differences in order to maintain body temperature and minimize evaporative water loss. When they adopt a darker coloration, their body temperature will warm more rapidly with
3410-414: Is known as oviparity , in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish
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3520-424: Is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs. Many animals feed on eggs. For example, principal predators of the black oystercatcher 's eggs include raccoons , skunks , mink , river and sea otters , gulls , crows and foxes . The stoat ( Mustela erminea ) and long-tailed weasel ( M. frenata ) steal ducks' eggs. Snakes of
3630-415: Is no need of cryptic colors. However, some have suggested that the protoporphyrin markings on passerine eggs actually act to reduce brittleness by acting as a solid-state lubricant. If there is insufficient calcium available in the local soil, the egg shell may be thin, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in
3740-446: Is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs. The default colour of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds, mainly passerines , produce coloured eggs. The colour comes from pigments deposited on top of the calcium carbonate base; biliverdin and its zinc chelate , and bilirubin , give
3850-424: Is often limited due to males forcing copulations. Mating primarily occurs on the branches of trees, making females very visible to males. Unpaired males may also intercept females by waiting at the base of a tree. Matings from male interception are often from genetically undesirable males. Over 90% of females mate with ten or more males in the production of a single clutch. The female grey foam-nest tree frog begins
3960-473: Is proportional to the percentage of fertilised ovules. For example, with watermelon , about a thousand grains of pollen must be delivered and spread evenly on the three lobes of the stigma to make a normal sized and shaped fruit. Outcrossing , or cross-fertilisation, and self-fertilisation represent different strategies with differing benefits and costs. An estimated 48.7% of plant species are either dioecious or self-incompatible obligate outcrossers. It
4070-413: Is the process in angiosperms (flowering plants) in which two sperm from each pollen tube fertilise two cells in a female gametophyte (sometimes called an embryo sac) that is inside an ovule. After the pollen tube enters the gametophyte, the pollen tube nucleus disintegrates and the two sperm cells are released; one of the two sperm cells fertilises the egg cell (at the bottom of the gametophyte near
4180-407: Is thought to act as a shock absorber, protecting the calcite shell from fracture during incubation, such as colliding with other eggs in the nest. Most bird eggs have an oval shape , with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct . Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and
4290-601: Is usually identical save for a fraction of their genes; each gamete is therefore genetically unique. At fertilisation, parental chromosomes combine. In humans , (2²²)² = 17.6x10 chromosomally different zygotes are possible for the non-sex chromosomes, even assuming no chromosomal crossover . If crossover occurs once, then on average (4²²)² = 309x10 genetically different zygotes are possible for every couple, not considering that crossover events can take place at most points along each chromosome. The X and Y chromosomes undergo no crossover events and are therefore excluded from
4400-399: Is usually motile whereas the female gamete cell, the ovum , is generally larger and sessile . The male and female gametes combine to produce the zygote cell. In multicellular organisms, the zygote subsequently divides in an organised manner into smaller more specialised cells, so that this new individual develops into an embryo . In most animals, the embryo is the sessile initial stage of
4510-559: The conceptus and such medical literature refers to the "products of conception" as the post-implantation embryo and its surrounding membranes. The term "conception" is not usually used in scientific literature because of its variable definition and connotation. Insects in different groups, including the Odonata ( dragonflies and damselflies ) and the Hymenoptera ( ants , bees , and wasps ) practise delayed fertilisation. Among
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4620-463: The benthic zone (associated with or occurring on the bottom of a body of water). Maturity is achieved within six to eight weeks. Male grey foam-nest tree frogs typically do not fight with other males of their species. Currently, there is nothing known about kin recognition and larval sibling competition in this species. Adaptations These frogs often live in arid and semi-arid climates and have developed several adaptations to live months at
4730-414: The coelacanths can reach a size of 9 cm (3.5 in) in diameter, and the young go through full development while in the uterus , living on the copious yolk. Animals are commonly classified by their manner of reproduction, at the most general level distinguishing egg-laying (Latin. oviparous ) from live-bearing (Latin. viviparous ). These classifications are divided into more detail according to
4840-436: The fruit . With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule. The growth of the pollen tube is controlled by the vegetative (or tube) cytoplasm. Hydrolytic enzymes are secreted by the pollen tube that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows. During pollen tube growth towards
4950-426: The haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation. In antiquity, Aristotle conceived the formation of new individuals through fusion of male and female fluids, with form and function emerging gradually, in a mode called by him as epigenetic . In 1784, Spallanzani established the need of interaction between
5060-592: The planula , and either develops directly into the adult animals or forms new adult individuals through a process of budding . Microlecithal eggs require minimal yolk mass. Such eggs are found in flatworms , roundworms , annelids , bivalves , echinoderms , the lancelet and in most marine arthropods . In anatomically simple animals, such as cnidarians and flatworms, the fetal development can be quite short, and even microlecithal eggs can undergo direct development. These small eggs can be produced in large numbers. In animals with high egg mortality, microlecithal eggs are
5170-407: The pollen grain germinates , and a pollen tube grows and penetrates the ovule through a tiny pore called a micropyle . The sperm are transferred from the pollen through the pollen tube to the ovule where the egg is fertilised. In flowering plants , two sperm cells are released from the pollen tube, and a second fertilisation event occurs involving the second sperm cell and the central cell of
5280-407: The salamanders . Eggs with a large yolk are called macrolecithal. The eggs are usually few in number, and the embryos have enough food to go through full fetal development in most groups. Macrolecithal eggs are only found in selected representatives of two groups: Cephalopods and vertebrates . Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of
5390-506: The Odonata, females may mate with multiple males, and store sperm until the eggs are laid. The male may hover above the female during egg-laying (oviposition) to prevent her from mating with other males and replacing his sperm; in some groups such as the darters, the male continues to grasp the female with his claspers during egg-laying, the pair flying around in tandem. Among social Hymenoptera, honeybee queens mate only on mating flights, in
5500-469: The Vegetable Kingdom (pages 466-467) summed up his findings in the following way. "It has been shown in the present volume that the offspring from the union of two distinct individuals, especially if their progenitors have been subjected to very different conditions, have an immense advantage in height, weight, constitutional vigour and fertility over the self-fertilised offspring from one of
5610-557: The ZP3 and is important for binding with the sperm and activating the acrosome reaction. ZP3 is sufficient though unnecessary for sperm/egg binding. Two additional sperm receptors exist: a 250kD protein that binds to an oviduct secreted protein, and SED1, which independently binds to the zona. After the acrosome reaction, the sperm is believed to remain bound to the zona pellucida through exposed ZP2 receptors. These receptors are unknown in mice but have been identified in guinea pigs. In mammals,
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#17327656353345720-469: The ability to store sperm for extended periods of time and can fertilise their eggs at their own desire. Oviparous animals producing eggs with thin tertiary membranes or no membranes at all, on the other hand, use external fertilisation methods. Such animals may be more precisely termed ovuliparous. External fertilisation is advantageous in that it minimises contact (which decreases the risk of disease transmission), and greater genetic variation. Sperm find
5830-406: The actual persistence of meiosis and self-fertilisation as a form of reproduction in long-established self-fertilising plants may be related to the immediate benefit of efficient recombinational repair of DNA damage during formation of germ cells provided by meiosis at each generation. The mechanics behind fertilisation has been studied extensively in sea urchins and mice. This research addresses
5940-412: The adult body, and by the yolk which the egg provides to nourish the embryo. Vertebrate eggs can be classified by the relative amount of yolk . Simple eggs with little yolk are called microlecithal , medium-sized eggs with some yolk are called mesolecithal , and large eggs with a large concentrated yolk are called macrolecithal . This classification of eggs is based on the eggs of chordates , though
6050-400: The advantage of reproductive assurance . Self-fertilisation can therefore result in improved colonisation ability. In some species, self-fertilisation has persisted over many generations. Capsella rubella is a self-fertilising species that became self-compatible 50,000 to 100,000 years ago. Arabidopsis thaliana is a predominantly self-fertilising plant with an out-crossing rate in
6160-540: The air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are viviparous ("live birth"). Dinosaurs laid eggs, some of which have been preserved as petrified fossils. Among mammals, early extinct species laid eggs, as do platypuses and echidnas (spiny anteaters). Platypuses and two genera of echidna are Australian monotremes . Marsupial and placental mammals do not lay eggs, but their unborn young do have
6270-407: The basic principle extends to the whole animal kingdom . Small eggs with little yolk are called microlecithal. The yolk is evenly distributed, so the cleavage of the egg cell cuts through and divides the egg into cells of fairly similar sizes. In sponges and cnidarians , the dividing eggs develop directly into a simple larva, rather like a morula with cilia . In cnidarians, this stage is called
6380-467: The binding of the spermatozoon to the GalT initiates the acrosome reaction . This process releases the hyaluronidase that digests the matrix of hyaluronic acid in the vestments around the oocyte. Additionally, heparin-like glycosaminoglycans (GAGs) are released near the oocyte that promote the acrosome reaction. Fusion between the oocyte plasma membranes and sperm follows and allows the sperm nucleus ,
6490-491: The biological sense. In placental mammals , the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus. Eggs are common among invertebrates , including insects , spiders , mollusks , and crustaceans . All sexually reproducing life, including both plants and animals, produces gametes . The male gamete cell, sperm ,
6600-467: The calculation. The mitochondrial DNA is only inherited from the maternal parent. Shortly after the sperm fuse with the egg, the two sperm centrioles form the embryo first centrosome and microtubule aster . The sperm centriole, found near the male pronucleus, recruit egg Pericentriolar material proteins forming the zygote first centrosome. This centrosome nucleates microtubules in the shape of stars called astral microtubules. The microtubules span
6710-403: The cells of incipient multicellular organisms. The cycle of the egg's formation is started by the gamete ovum being released ( ovulated ) and egg formation being started. The finished egg is then ovipositioned and eventual egg incubation can start. Scientists often classify animal reproduction according to the degree of development that occurs before the new individuals are expelled from
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#17327656353346820-401: The complex tissues that identify amniotes. The eggs of the egg-laying mammals (the platypus and the echidnas ) are macrolecithal eggs very much like those of reptiles . The eggs of marsupials are likewise macrolecithal, but rather small, and develop inside the body of the female, but do not form a placenta . The young are born at a very early stage, and can be classified as a " larva " in
6930-407: The course of several months. The grey foam-nest tree frog forms uric acid and excretes it from their body as a nitrogenous end product. Anywhere between fifty and seventy-five percent of total waste nitrogen is converted into uric acid, while the other twenty-five to fifty percent is expelled as urea in waste. This uric acid excreted can be released in a solid form and does not cause any water loss for
7040-474: The crowded cliff ledges on which they breed. Yolks of birds' eggs are yellow from carotenoids , it is affected by their living conditions and diet. Bird eggshells are diverse. For example: Tiny pores in bird eggshells allow the embryo to breathe. The domestic hen 's egg has around 7000 pores. Some bird eggshells have a coating of vaterite spherules , which is a rare polymorph of calcium carbonate. In Greater Ani Crotophaga major this vaterite coating
7150-475: The development that occurs before the offspring are expelled from the adult's body. Traditionally: The term hemotrophic derives from the Latin for blood-feeding, contrasted with histotrophic for tissue-feeding. Fertilization Fertilisation or fertilization (see spelling differences ), also known as generative fertilisation , syngamy and impregnation , is the fusion of gametes to give rise to
7260-555: The egg to develop without fertilisation or syngamy. The sperm may enter the egg. Hybridogenesis : One genome is eliminated to produce haploid eggs. Canina meiosis : (sometimes called "permanent odd polyploidy") one genome is transmitted in the Mendelian fashion, others are transmitted clonally. The major benefit of cross-fertilisation is generally thought to be the avoidance of inbreeding depression . Charles Darwin , in his 1876 book The Effects of Cross and Self Fertilisation in
7370-514: The eggs and care for young. This behavior is owed to their external fertilization mechanism. During the mating process, the female frog produces a foam nest, typically on branches that hang above bodies of water, in order to keep her eggs moist as they develop. This practice is what gives the grey foam-nest tree frogs their name. Grey foam-nest tree frogs are arboreal. Like other species in the genus Chiromantis , they have discs on their toes, and their outer two fingers are widely spaced and nearly at
7480-709: The eggs to be suspended in oxygenated water. Grey foam-nest tree frogs that reproduce on land create these nests to minimize drying out, temperature changes, and predation. Polyandry , an important characteristic of the grey foam nest tree frog, has proven to substantially increase offspring survival. Polyandrous matings may provide eggs with additional nutrients via the seminal fluid from multiple males. These nutrients increase yolk availability for post-hatching development and increases survival of tadpoles. Sperm competition may also allow for increased egg interaction with steroids in seminal fluids, which may accelerate yolk metabolism and increase growth rate of tadpoles. Offspring as
7590-405: The eggs via chemotaxis , a type of ligand/receptor interaction. Resact is a 14 amino acid peptide purified from the jelly coat of A. punctulata that attracts the migration of sperm. After finding the egg, the sperm penetrates the jelly coat through a process called sperm activation. In another ligand/receptor interaction, an oligosaccharide component of the egg binds and activates a receptor on
7700-412: The female provides different functions for aquatic and terrestrial breeding alike. Some grey foam-nest tree frogs breed exclusively in water. In these water-breeders, foam nests allow the eggs to be suspended in oxygenated water. Grey foam-nest tree frogs that reproduce on land create these nests to minimize drying out, temperature changes, and predation. Development occurs over a period of six days, with
7810-495: The female's eggs will be fertilized. A larger number of males means more sperm production, which therefore increases the likelihood the sperm are genetically compatible with the eggs and allows for a variety of different sperm-based traits. Female grey foam-nest tree frogs lay eggs which are quickly fertilized by the male soon afterwards. Females also create foam for nests. Grey foam-nest tree frogs show remarkable adaptability in their oviposition sites, as they may lay their eggs in
7920-585: The female's ovum and male's sperm to form a zygote in frogs. In 1827, Karl Ernst von Baer observed a therian mammalian egg for the first time. Oscar Hertwig (1876), in Germany, described the fusion of nuclei of spermatozoa and of ova from sea urchin . The evolution of fertilisation is related to the origin of meiosis , as both are part of sexual reproduction , originated in eukaryotes . One hypothesis states that meiosis originated from mitosis. The gametes that participate in fertilisation of plants are
8030-441: The formation of a diploid cell called a zygote . The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy . Embryonic implantation not in the uterine wall results in an ectopic pregnancy that can kill the mother. In such animals as rabbits, coitus induces ovulation by stimulating the release of the pituitary hormone gonadotropin; this release greatly increases
8140-399: The formation of a fertilisation cone . Mammals internally fertilise through copulation . After a male ejaculates , many sperm move to the upper vagina (via contractions from the vagina) through the cervix and across the length of the uterus to meet the ovum. In cases where fertilisation occurs, the female usually ovulates during a period that extends from hours before copulation to
8250-404: The frog. This is especially suitable for grey foam-nest tree frogs due to the fact that they primarily inhabit dry environments, where minimizing water loss is highly important. It is known that adults of both sexes of Afrixalus fornasinii prey on grey foam-nest tree frog eggs and tadpoles. This species is the first African anuran to demonstrate hetero-cannibalism by preying on eggs belonging to
8360-650: The genera Dasypeltis and Elachistodon specialize in eating eggs. Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos . Like amphibians, amniotes are air-breathing vertebrates , but they have complex eggs or embryos , including an amniotic membrane . Amniotes include reptiles (including dinosaurs and their descendants, birds) and mammals. Reptile eggs are often rubbery and are always initially white. They are able to survive in
8470-494: The individual life cycle, and is followed by the emergence (that is, the hatching) of a motile stage. The zygote or the ovum itself or the sessile organic vessel containing the developing embryo may be called the egg. A recent proposal suggests that the phylotypic animal body plans originated in cell aggregates before the existence of an egg stage of development . Eggs, in this view, were later evolutionary innovations , selected for their role in ensuring genetic uniformity among
8580-411: The larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die. A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally. However, the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from
8690-541: The likelihood of pregnancy. Fertilisation in humans is the union of a human egg and sperm , usually occurring in the ampulla of the fallopian tube , producing a single celled zygote , the first stage of life in the development of a genetically unique organism, and initiating embryonic development . Scientists discovered the dynamics of human fertilisation in the nineteenth century. The term conception commonly refers to "the process of becoming pregnant involving fertilisation or implantation or both". Its use makes it
8800-409: The micropyle (an opening in the ovule wall) and the pollen tube "bursts" into the embryo sac, releasing sperm. The growth of the pollen tube has been believed to depend on chemical cues from the pistil, however these mechanisms were poorly understood until 1995. Work done on tobacco plants revealed a family of glycoproteins called TTS proteins that enhanced growth of pollen tubes. Pollen tubes in
8910-411: The micropyle), forming a diploid (2n) zygote . This is the point when fertilisation actually occurs; pollination and fertilisation are two separate processes. The nucleus of the other sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the gametophyte. The resulting cell is triploid (3n). This triploid cell divides through mitosis and forms the endosperm ,
9020-418: The mother also providing direct nourishment. The eggs of fish and amphibians are jellylike. Cartilaginous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have
9130-405: The mother ensuring the eggs stay moist the day after mating. Egg mortality in foam nesting tree frogs remains mostly unexplored, therefore information regarding the matter is limited. Grey foam-nest tree frogs' egg mortality is considered moderate compared to other anuran species. Following the embryonic development, a tadpole breaks free and drops into the water below the foam nest. Tadpoles live in
9240-415: The mother, or in some cases genetically differ from her but inherit only part of her DNA. Parthenogenesis occurs in many plants and animals and may be induced in others through a chemical or electrical stimulus to the egg cell. In 2004, Japanese researchers led by Tomohiro Kono succeeded after 457 attempts to merge the ova of two mice by blocking certain proteins that would normally prevent the possibility;
9350-432: The mother. The mother then gives birth to relatively mature young. In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism . In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous , with the egg being fertilized and developed internally, but with
9460-421: The norm, as in bivalves and marine arthropods. However, the latter are more complex anatomically than e.g. flatworms, and the small microlecithal eggs do not allow full development. Instead, the eggs hatch into larvae , which may be markedly different from the adult animal. In placental mammals, where the embryo is nourished by the mother throughout the whole fetal period, the egg is reduced in size to essentially
9570-421: The ovary, the generative nucleus divides to produce two separate sperm nuclei (haploid number of chromosomes) – a growing pollen tube therefore contains three separate nuclei, two sperm and one tube. The sperms are interconnected and dimorphic, the large one, in a number of plants, is also linked to the tube nucleus and the interconnected sperm and the tube nucleus form the "male germ unit". Double fertilisation
9680-444: The oviduct and the ampulla, and chemotactic gradients of progesterone have been confirmed as the signal emanating from the cumulus oophorus cells surrounding rabbit and human oocytes. Capacitated and hyperactivated sperm respond to these gradients by changing their behaviour and moving towards the cumulus-oocyte complex. Other chemotactic signals such as formyl Met-Leu-Phe (fMLF) may also guide spermatozoa. The zona pellucida ,
9790-405: The ovule, which is a second female gamete. Unlike animal sperm which is motile, the sperm of most seed plants is immotile and relies on the pollen tube to carry it to the ovule where the sperm is released. The pollen tube penetrates the stigma and elongates through the extracellular matrix of the style before reaching the ovary. Then near the receptacle, it breaks through the ovule through
9900-410: The pointed end develops at the back.. One hypothesis is that long, pointy eggs are an incidental consequence of having a streamlined body typical of birds with strong flying abilities; flight narrows the oviduct, which changes the type of egg a bird can lay. Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait
10010-603: The pollen tube to release sperm in Arabidopsis has been shown to depend on a signal from the female gametophyte. Specific proteins called FER protein kinases present in the ovule control the production of highly reactive derivatives of oxygen called reactive oxygen species (ROS). ROS levels have been shown via GFP to be at their highest during floral stages when the ovule is the most receptive to pollen tubes, and lowest during times of development and following fertilisation. High amounts of ROS activate Calcium ion channels in
10120-491: The pollen tube, causing these channels to take up Calcium ions in large amounts. This increased uptake of calcium causes the pollen tube to rupture, and release its sperm into the ovule. Pistil feeding assays in which plants were fed diphenyl iodonium chloride (DPI) suppressed ROS concentrations in Arabidopsis , which in turn prevented pollen tube rupture. After being fertilised, the ovary starts to swell and develop into
10230-475: The process of reproduction by producing a thick mucus-like fluid from its cloaca (a cavity at the end of the digestive tract in amphibians). During this process, the frog uses its hind legs to whip the mucus into elastic froth that will eventually serve as physical protection for the developing eggs. The female will leave temporarily to rehydrate before returning to the nest. Nest construction can take around five to six hours. Males then incorporate their sperm into
10340-546: The question of how the sperm and the appropriate egg find each other and the question of how only one sperm gets into the egg and delivers its contents. There are three steps to fertilisation that ensure species-specificity: Consideration as to whether an animal (more specifically a vertebrate) uses internal or external fertilisation is often dependent on the method of birth. Oviparous animals laying eggs with thick calcium shells, such as chickens , or thick leathery shells generally reproduce via internal fertilisation so that
10450-442: The recently laid foam, fertilizing them. The next day, the female will return to its egg-laying site and add a layer of foam to protect the eggs from drying out. Foam-nest building behaviors and patterns have evolved several times. The foam nest made by the female provides different functions for aquatic and terrestrial breeding alike. Some grey foam-nest tree frogs breed exclusively in water. In these water-breeders, foam nests allow
10560-465: The resulting embryo normally developed into a mouse. Allogamy , which is also known as cross-fertilisation, refers to the fertilisation of an egg cell from one individual with the male gamete of another. Autogamy which is also known as self-fertilisation, occurs in such hermaphroditic organisms as plants and flatworms; therein, two gametes from one individual fuse. Some relatively unusual forms of reproduction are: Gynogenesis : A sperm stimulates
10670-490: The same parents. And this fact is amply sufficient to account for the development of the sexual elements, that is, for the genesis of the two sexes." In addition, it is thought by some, that a long-term advantage of out-crossing in nature is increased genetic variability that promotes adaptation or avoidance of extinction (see Genetic variability ). Chiromantis xerampelina The grey foam-nest tree frog ( Chiromantis xerampelina ), or southern foam-nest tree frog ,
10780-566: The small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote . In addition to bony fish and cephalopods, macrolecithal eggs are found in cartilaginous fish , reptiles , birds and monotreme mammals. The eggs of
10890-547: The smallest known bird egg, which measures between 6.35–11.4 millimetres (0.250–0.449 in) long and weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects, and other invertebrates can be even smaller. Reproductive structures similar to the egg in other kingdoms are termed " spores ", or in spermatophytes " seeds ", or in gametophytes "egg cells". Several major groups of animals typically have readily distinguishable eggs. The most common reproductive strategy for fish
11000-415: The soil. For the same reason, later eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted. The color of individual eggs is also genetically influenced, and appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex-determining W chromosome (female birds are WZ, males ZZ). It used to be thought that color
11110-410: The sperm (male) and the egg (female) cell. Various plant groups have differing methods by which the gametes produced by the male and female gametophytes come together and are fertilised. In bryophytes and pteridophytic land plants, fertilisation of the sperm and egg takes place within the archegonium . In seed plants , the male gametophyte is formed within a pollen grain. After pollination ,
11220-435: The sperm and causes the acrosomal reaction . The acrosomal vesicles of the sperm fuse with the plasma membrane and are released. In this process, molecules bound to the acrosomal vesicle membrane, such as bindin, are exposed on the surface of the sperm. These contents digest the jelly coat and eventually the vitelline membrane. In addition to the release of acrosomal vesicles, there is explosive polymerisation of actin to form
11330-501: The sperm fertilises the egg without having to pass through the thick, protective, tertiary layer of the egg. Ovoviviparous and viviparous animals also use internal fertilisation. Although some organisms reproduce via amplexus , they may still use internal fertilisation, as with some salamanders. Advantages of internal fertilisation include minimal waste of gametes, greater chance of individual egg fertilisation, longer period of egg protection, and selective fertilisation. Many females have
11440-403: The sun's radiation. It is common for frogs to do this when the air temperature is below 36 °C. White coloration helps them maintain a temperature below the ambient temperature by reflecting heat away. Their skin is resistant to evaporation that rivals terrestrial reptiles, earning them the nickname of "waterproof frogs", but this resistance is not present in their ventral skin. When met with
11550-488: The typical centriole , and atypical centriole that is attached to the flagellum , but not the mitochondria , to enter the oocyte. The protein CD9 likely mediates this fusion in mice (the binding homolog). The egg " activates " itself upon fusing with a single sperm cell and thereby changes its cell membrane to prevent fusion with other sperm. Zinc atoms are released during this activation. This process ultimately leads to
11660-534: The whole valium of the egg, allowing the egg pronucleus to use the cables to get to the male pronucleus. As the male and female pronuclei approach each other, the single centrosome split into two centrosomes located in the interphase between the pronuclei. Then the centrosome via the astral microtubules polarises the genome inside the pronuclei. Organisms that normally reproduce sexually can also reproduce via parthenogenesis , wherein an unfertilised female gamete produces viable offspring. These offspring may be clones of
11770-537: The wild of less than 0.3%; a study suggested that self-fertilisation evolved roughly a million years ago or more in A. thaliana . In long-established self-fertilising plants, the masking of deleterious mutations and the production of genetic variability is infrequent and thus unlikely to provide a sufficient benefit over many generations to maintain the meiotic apparatus. Consequently, one might expect self-fertilisation to be replaced in nature by an ameiotic asexual form of reproduction that would be less costly. However
11880-431: The yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage. A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish , even though their eggs can be quite small. Despite their macrolecithal structure,
11990-439: Was 30 cm × 14 cm × 9 cm (11.8 in × 5.5 in × 3.5 in) in size. Whale shark eggs typically hatch within the mother. At 1.5 kg (3.3 lb) and up to 17.8 cm × 14 cm (7.0 in × 5.5 in), the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some non-avian dinosaurs laid larger eggs. The bee hummingbird produces
12100-456: Was applied to the shell immediately before laying, but subsequent research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral. In species such as the common guillemot , which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own eggs on
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