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Encyclopedia > Fertilisation
A sperm cell fertilising an ovum
A sperm cell fertilising an ovum

Fertilisation (also known as conception, fecundation and syngamy), is fusion of gametes to form a new organism of the same species. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external fertilisation. Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. ... Image File history File links Sperm-egg. ... Image File history File links Sperm-egg. ... Soil Fertilization or Crop Fertilization are methods of improving soil quality with a view towards improving soil fertility. ... Look up conception in Wiktionary, the free dictionary. ...


The entire process of development of new individuals is called procreation, the act of species reproduction. Reproduction is the creation of one thing as a copy of, product of, or replacement for a similar thing, e. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ...

Contents

Fertilization in plants

Flowering plants

After the pistil is pollinated, the pollen grain germinates in a response to a sugary fluid secreted by the mature stigma called semen. From each pollen grain, a pollen tube grows out attempting to travel into the ovary by creating a path through the female tissue. The vegetative (or tube) and generative nuclei of the pollen grain pass into its respective pollen tube. The growth of the pollen tube is controlled by the vegetative (or tube) nucleus. Hydrolytic enzymes are secreted by the pollen tube to digest the female tissue (stigma and style) as the pollen tube grows. During pollen tube growth toward the ovary, the generative nucleus divides to produce two separate sperm nuclei - a growing pollen tube therefore contains 3 separate nuclei. The pollen tube does not directly reach the ovary in a straight line. It travels near the skin of the style and curls to the bottom of the ovary, then near the receptacle, it breaks through the ovule through the micropyle (an opening in the ovule wall) and reaches the ovum (or egg cell) to fertilise it. This is the point when fertilisation actually occurs. Note the pollination and fertilisation are two separate processes. After being fertilised, the ovary starts to swell and will develop a fruit. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule. The Pistil is the part of the flower made up of one or more carpels. ... Carpenter bee with pollen collected from Night-blooming cereus Pollination is an important step in the reproduction of seed plants: the transfer of pollen grains (male gametes) to the plant carpel, the structure that contains the ovule (female gamete). ... Pollen may refer to the microspores of either angiosperms (flowering plants) or gymnosperms (conifers and cycads). ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ... Amaryllis style and stigmas A carpel is the outer, often visible part of the female reproductive organ of a flower; the basic unit of the gynoecium. ... This article or section does not adequately cite its references or sources. ... For other uses, see Fruit (disambiguation). ... Categories: Biological reproduction | Biology stubs ...


The process is easy to visualize if one looks at maize silk, which is the female flower of corn. Pollen from the tassel (the male flower) falls on the sticky external portion of the silk, and then pollen tubes grow down the silk to the attached ovule. The dried silk remains inside the husk of the ear as the seeds mature; if one carefully removes the husk, the floral structures may be seen. In many plants, the development of the flesh of the fruit 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. This article is about the maize plant. ... For other uses, see hilt and maize. ... For the political designation, see Eco-socialism. ...


Double fertilization

Double fertilization refers to the process in angiosperms (flowering plants) during reproduction, in which two sperm nuclei from each pollen tube fertilise two cells in an ovary. The pollen grain adheres to the stigma of the carpel (female reproductive structure) and grows a pollen tube that penetrates the ovum through a tiny pore called a micropyle. Two sperm cells (derived from the generative nucleus) are released into the ovary through this tube. One of the two sperm cells fertilities the egg cell (at the end of the ovary), forming a diploid (2n) zygote. The other sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the embryo sac (or ovule). The resulting cell is triploid (3n). This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue inside the fruit. Classes Magnoliopsida - Dicots Liliopsida - Monocots The flowering plants (also angiosperms or Magnoliophyta) are one of the major groups of modern plants, comprising those that produce seeds in specialized reproductive organs called flowers, where the ovulary or carpel is enclosed. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... For other uses, see Sperm (disambiguation). ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Longitudinal section of female flower of squash showing ovary, ovules, pistil, and petals In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. ... SEM image of pollen grains from a variety of common plants: sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis). ... Amaryllis style and stigmas A carpel is the female reproductive organ of a flower; the basic unit of the gynoecium. ... Amaryllis style and stigmas A carpel is the outer, often visible part of the female reproductive organ of a flower; the basic unit of the gynoecium. ... Pollen may refer to the microspores of either angiosperms (flowering plants) or gymnosperms (conifers and cycads). ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... Location of ovules inside a Helleborus foetidus flower Ovule literally means small egg. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... It has been suggested that Biparental zygote be merged into this article or section. ... For other uses, see Embryo (disambiguation). ... Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than one copy (ploidy) of their chromosomes. ... Mitosis divides genetic information during cell division. ... Endosperm is the tissue produced in the seeds of most flowering plants around the time of fertilization. ... A nutrient is either a chemical element or compound used in an organisms metabolism or physiology. ... Biological tissue is a group of cells that perform a similar function. ... For other uses, see Fruit (disambiguation). ...


The two central cell maternal nuclei (polar nuclei) that contribute to the endosperm arise by mitosis from a single meiotic product. Therefore, maternal contribution to the genetic constitution of the triploid endosperm is different from that of the embryo.


Recently, research has shown that in one primitive group of flowering plants, the water lilies, Nuphar, the endosperm is diploid, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei.[1] Species About 10-15 species, including: Nuphar advena Nuphar japonica Nuphar kalmiana Nuphar lutea- Yellow Water-lily Nuphar microphylla Nuphar orbiculata Nuphar polysepala Nuphar pumila- Least Water-lily Nuphar rubrodisca Nuphar saggitifolia Nuphar shimadae Nuphar ulvacea Nuphar variegata Nuphar is genus of aquatic plants in the family Nymphaeaceae, with a...


In gymnosperms, such as conifers, the food storage tissue is part of the female gametophyte only, a haploid (1n) tissue, so there is no double fertilisation. Gymnosperms are seed-bearing, vascular plants. ... In plants that undergo alternation of generations, a gametophyte is the structure, or phase of life, that contains only half of the total complement of chromosomes: The sporophyte produces spores, in a process called meiosis. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ...


Fertilisation in animals

The mechanics behind fertilisation has been studied extensively in sea urchins and mice. This research addresses 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 insure species-specificity: 1. Chemotaxis 2. Sperm activation/acrosomal reaction 3. Sperm/egg adhesion. A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ...


Sea urchins

Acrosome reaction on a Sea Urchin cell
Acrosome reaction on a Sea Urchin cell

Chemotaxis was discovered as the method for which sperm find the eggs. This chemotaxis is an example of a ligand/receptor interaction. Resact is a 14 amino acid peptide purified from the jelly coat of A. punctulata that attracts the migration of sperm. Image File history File links Acrosome_reaction_diagram. ... Image File history File links Acrosome_reaction_diagram. ... Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ...


After finding the egg, the sperm gets through 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 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 polymerization of actin to form a thin spike at the head of the sperm called the acrosomal process. In spermatozoa of many animals, the acrosome is an organelle that develops over the anterior half of the spermatozoons head. ... In sperm cells of many higher animals, the acrosome develops over the anterior half of its head. ...


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 ERB1. As soon as the spermatozoön has entered the yolk, the peripheral portion of the latter is transformed into a membrane, the vitelline membrane which prevents the passage of additional spermatozoa. ... Erb1 is a protein required for maturation of the 25S and 5. ...


Fusion of the plasma membranes of the sperm and egg are likely mediated by bindin. At the site of contact, fusion causes the formation of a fertilisation cone.


Mammals

All mammals rely on internal fertilisation through copulation. To deliver the sperm to the female, the male inserts his sexual organ, the penis, into the opening of the vagina, the passage into the female's other sexual organs. Once the male ejaculates, a large number of sperm cells swim from the upper vagina through the cervix and across the length of the uterus toward the ovum—a considerable distance compared to the size of the sperm cell. The capacitated spermatozoon and the oocyte meet and interact in the ampulla of the fallopian tube. It is probable that chemotaxis is involved in directing the sperm to the egg, but the mechanism has yet to be worked out. Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... A pair of lions copulating in the Maasai Mara, Kenya. ... For other uses, see Female (disambiguation). ... This article is about the Male sex. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body (which are not always bodily organs according to the strict definition) which are involved in sexual reproduction and constitute the reproductive system in an complex organism; namely: Male: penis (notably the glans penis... The penis (plural penises, penes) is an external male sexual organ. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... This article is about male ejaculation. ... The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... This article is about female reproductive anatomy. ... Capacitation refers to the post-ejaculatory process that takes place in mammalian spermatozoa that renders them competent to interact with, and fertilize, an oocyte. ... The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx) are two very fine tubes leading from the ovaries of female mammals into the uterus. ... Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ...


After finding the egg, the sperm binds to the zona pellucida. In contrast to sea urchins, the sperm binds to the egg before the acrosmal reaction. The zona pellucida is a thick layer of extracellular matrix that surrounds the egg and is similar to the role of the vitelline membrane in sea urchins. A glycoprotein in the zona pellucida, ZP3 was discovered to be responsible for egg/sperm adhesion in mice. The receptor galactosyltransferase (GalT) binds to the N-acetylglucosamine residues on the ZP3 and is important for binding to sperm and activating the acrosome reaction. ZP3 is sufficient for sperm/egg binding but not necessary. There are two additional sperm receptors: a 250kD protein that binds to an oviduct secreted protein and SED1 which binds independently to the zona. After the acrosome reaction, it is believed that the sperm remains bound to the zona pellucida through exposed ZP2 receptors. These receptors are unknown in mice but have been identified in guinea pigs. The zona pellucida (or zona striata in older texts) is a glycoprotein membrane surrounding the plasma membrane of an oocyte. ... ZP3 is the receptor in the zona pellucida which binds with the acrosome of the sperm in the acrosome reaction. ... Galactosyltransferases are a type of glycosyltransferase that catalyze the transfer of a galactose. ...


In mammals, binding of the spermatozoon to the GalT initiates the acrosome reaction. This process releases the enzyme hyaluronidase, which digests the matrix of hyaluronic acid in the vestments surrounding the oocyte. Fusion between the sperm and oocyte plasma membranes follows, allowing the entry of the sperm nucleus, mitochondria, centriole and flagellum into the oocyte. The fusion is likely mediated by the protein CD9 in mice (the bindin homolog). Once the ovum fuses with a single sperm cell, its cell membrane changes, preventing fusion with other sperm (see Egg activation). In sperm cells of many higher animals, the acrosome develops over the anterior half of its head. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Hyaluronidase The hyaluronidases (EC 3. ... Hyaluronan (also called hyaluronic acid or hyaluronate) is a glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... A centriole showing the nine triplets of microtubules. ... For the insect anatomical structure, see Antenna (biology). ... After the fusion of the sperm plasma membrane and the egg plasma membrane after fertilization, animal eggs go through a process called egg activation to prepare the egg for development. ...


This process ultimately leads to the formation of a diploid cell called a zygote. The zygote begins to divide and form a blastocyst and when it reaches the uterus, it performs implantation in the endometrium. At this point the female is said to be pregnant. If the embryo emplants in any tissue other than the uterine wall, an ectopic pregnancy results, which can be fatal to the mother. Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... It has been suggested that Biparental zygote be merged into this article or section. ... The blastocyst is an early stage of the human (or any other mammal) development early in pregnancy. ... Implantation is a phenomenon in prenatal development, i. ... This article is about human pregnancy in biological females. ... This article is about female reproductive anatomy. ...


In some animals (e.g. rabbit) the act of coitus induces ovulation by stimulating release of the pituitary hormone gonadotropin. This greatly increases the probability that coitus will result in pregnancy.


Humans

Main article: Human fertilisation

The term "conception" commonly refers to fertilisation, but is sometimes defined as implantation or even "the point at which human life begins," and is thus a subject of semantic arguments about the beginning of pregnancy, within the abortion debate. Gastrulation is the point in development when the implanted blastocyst develops three germ layers, the endoderm, the exoderm and the mesoderm. It is at this point that the genetic code of the father becomes fully involved in the development of the embryo. Until this point in development, twinning is possible. Additionally, interspecies hybrids which have no chance of development survive until gastrulation. However this stance is not entirely warranted since human developmental biology literature refers to the "conceptus" and the medical literature refers to the "products of conception" as the post-implantation embryo and its surrounding membranes.[2] The term "conception" is not usually used in scientific literature because of its variable definition and connotation. Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. ... Controversy over the beginning of pregnancy usually occurs in the context of the abortion debate. ...


Fertilisation and genetic recombination

Meiosis results in a random segregation of the genes contributed from each parent. Each parent organism generally has the same genetic make-up, but differs for a fraction of their genes. Therefore, each gamete produced by a person will be genetically different from the others from that person, as well as from the gametes produced by another person. When gametes first fuse at fertilisation, the chromosomes donated by the parents are combined, and, in humans, this means that (2²²)² (17,592,186,044,416 possible zygotes), chromosomally different zygotes are possible for the non-sex chromosomes, even assuming no chromosomal crossover. If crossover occurs once, then on average (4²²)² (309,485,009,821,274,699,980,603,392) 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 do not undergo crossover events, so are excluded from the calculation. Note that the mitochondrial DNA is only inherited from the maternal parent. For the figure of speech, see meiosis (figure of speech). ... A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... A scheme of a condensed (metaphase) chromosome. ... A parent is a father or mother; one who begets or one who gives birth to or nurtures and raises a child; a relative who plays the role of guardian // Mother This article or section does not cite its references or sources. ... This article is about modern humans. ... It has been suggested that Biparental zygote be merged into this article or section. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... Mitochondrial DNA (some captions in German) Mitochondrial DNA (mtDNA) is the DNA located in organelles called mitochondria. ...


Parthenogenesis

Another method of fertilisation occurs among animals that normally reproduce sexually, through parthenogenesis: when the gamete of a female is not fertilised by a male, yet produces viable and unique offspring that are not clones. Only DNA from the mother is inherited, but it is not identical to her. Normal eggs of the mother become fertilised, without sperm, and development proceeds normally. This occurs naturally in several species and may be induced in others through a chemical or electrical stimulus. In 2004, Japanese researchers led by Tomohiro Kono succeeded after 457 attempts to merge the ovums of two mice, the result of which developed normally into a mouse. This was achieved by blocking certain proteins that would normally prevent the possibility. [1][2] For the religious belief, see Virgin Birth of Jesus. ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ...


See also

Kaguya (born in 2004) is a mouse that has two parents of the same sex. ... Female sperm is the theoretical concept of a process in which partly developed sperm cells, otherwise known as spermatogonial stem cells, would be created from a females bone marrow stem cells. ... For the Inter-Varsity Fellowship, see Universities and Colleges Christian Fellowship. ... Fetal (U.S. English; Foetal UK English) development is the process in which a fetus (U.S. English; Foetus UK English) develops during gestation, from the times of conception until birth. ... Superfetation (also spelt superfoetation, based on a false etymology — see fetus) is the formation of a fetus while another fetus is already present in the uterus. ... Superfecundation is the fertilisation of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. ...

Notes and references

  1. ^ Friedman, W. E. & J. H. Williams (2003). Modularity of the angiosperm female gametophyte and its bearing on the early evolution of endosperm in flowering plants. Evolution 57 (2): 216-30. 
  2. ^ Moore, K. L. & T. V. M. Persaud (2003). The Developing Human: Clinically Oriented Embryology. W. B. Saunders Company. ISBN 0-7216-6974-3. 

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