A sperm cell fertilising an ovum

For soil improvement see Fertilization (soil).

Fertilisation^[1] (also known as conception, fecundation and syngamy), is fusion of gametes to produce a new organism of the same species. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete 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.

The entire process of development of new individuals is called procreation, the act of species reproduction. Reproduction is the Biological process by which new individual Organisms are produced Reproduction is the Biological process by which new individual Organisms are produced

Fertilisation 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. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. Pollination in angiosperms and Gymnosperms is the process that transfers pollen grains, which contain the male Gametes (sperm to where the female From each pollen grain, a pollen tube grows out attempting to travel into the ovary by creating a path through the female tissue. The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants 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. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins During pollen tube growth toward the ovary, the generative nucleus divides to produce two separate sperm nuclei - a growing pollen tube therefore contains three 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. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells This is the point when fertilisation actually occurs. Note that pollination and fertilisation are two separate processes. After being fertilised, the ovary starts to swell and will develop a fruit. The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule.

The process is easy to visualize if one looks at maize silk, which is the female flower of corn. Maize (ˈmeɪz ( Zea mays L. ssp mays) known as corn in some countries is a cereal grain domesticated in Mesoamerica 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. For other uses see Hilt and Maize. A tassel is a binding of Plaited or otherwise gathered threads from which at one 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. Watermelon ( Citrullus lanatus ( Thunb) Matsum & Nakai family Cucurbitaceae) refers to both Fruit and Plant of a vine-like (climber

Double fertilisation

Double fertilisation is the process in angiosperms (flowering plants) during reproduction, in which two sperm nuclei from each pollen tube fertilise two cells in an ovary. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Reproduction is the Biological process by which new individual Organisms are produced The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In the Flowering plants an ovary is a part of the female reproductive organ of the flower or Gynoecium. 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. Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells Two sperm cells (derived from the generative nucleus) are released into the ovary through this tube. One of the two sperm cells fertilises the egg cell (at the end of the ovary), forming a diploid (2n) zygote. "Haplo" redirects here For the fictional character see The Death Gate Cycle. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" The other sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the embryo sac (or ovule). An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular The resulting cell is triploid (3n). Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, inside the seed. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Endosperm is the tissue produced in the Seeds of most Flowering plants around the time of fertilization A nutrient is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment Tissue is a cellular organizational level intermediate between cells and a complete organism A seed (in some plants referred to as a kernel) is a small embryonic Plant enclosed in a covering called the seed coat usually with some stored

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. Nuphar is genus of Aquatic plants in the family Nymphaeaceae, with a temperate Northern Hemisphere distribution ^[2]

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. Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are In Plants and Algae that undergo Alternation of generations, a gametophyte is the multicellular structure or phase that is Haploid, containing "Haplo" redirects here For the fictional character see The Death Gate Cycle.

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. A spermatozoon or spermatozoan ( pl spermatozoa) from the Ancient Greek σπέρμα (seed and ζῷον (living being and more commonly known There are three steps to fertilisation that insure species-specificity:

1. Chemotaxis
2. Sperm activation/acrosomal reaction
3. Sperm/egg adhesion.

Sea urchins

Acrosome reaction on a Sea Urchin cell

Chemotaxis was discovered as the method by which sperm find the eggs. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements 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.

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. During Fertilization, the acrosome reaction is the reaction which occurs in the Acrosome of the Sperm as it approaches the egg. 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 (also known as sperm/sperm cell of many animals the Acrosome is an Organelle that develops over the anterior half of the sperm's head

The sperm binds to the egg through another ligand reaction between receptors on the vitelline membrane. The vitelline membrane is a structure directly adjacent to the outer surface of the Plasma membrane of an Ovum. The sperm surface protein bindin, binds to a receptor on the vitelline membrane identified as ERB1. Erb1 also known as the eukaryotic ribosome biogenesis protein 1 is a Yeast 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. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Sexual intercourse, in its biological sense is the act in which the male reproductive organ (in humans and other higher animals enters the female reproductive tract 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. Female (♀ is the Sex of an Organism, or a part of an organism which produces ova (egg cells Male (♂ refers to the sex of an organism or part of an organism which produces small mobile Gametes called spermatozoa. A sex organ, or primary sexual characteristic, as narrowly defined is any of the anatomical parts of the body which are involved in sexual reproduction and constitute The penis (plural penises, penes The vagina (from Latin, literally " Sheath " or " Scabbard " is a fibromuscular tubular tract leading from the Uterus 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. Ejaculation is the ejecting of Semen from the Penis, and is usually accompanied by Orgasm. The cervix (from Latin "neck" is the lower narrow portion of the Uterus where it joins with the top end of the Vagina. The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the The capacitated spermatozoon and the oocyte meet and interact in the ampulla of the fallopian tube. This article is about a biological process related to reproduction for the other use see Capacitation (NGO. The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges ( singular salpinx) are two very fine tubes lined with ciliated It is probable that chemotaxis is involved in directing the sperm to the egg, but the mechanism has yet to be worked out. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements

After finding the egg, the sperm binds to the zona pellucida. The zona pellucida (or zona striata in older texts is a Glycoprotein membrane surrounding the Plasma membrane of an Oocyte. 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. ZP3 is the receptor in the Zona pellucida which binds with the Acrosome of the Sperm in the Acrosome reaction. 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. Galactosyltransferases are a type of Glycosyltransferase that Catalyze the transfer of a Galactose. 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.

In mammals, binding of the spermatozoon to the GalT initiates the acrosome reaction. During Fertilization, the acrosome reaction is the reaction which occurs in the Acrosome of the Sperm as it approaches the egg. This process releases the enzyme hyaluronidase, which digests the matrix of hyaluronic acid in the vestments surrounding the oocyte. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins The hyaluronidases ( are a family of Enzymes that degrade Hyaluronic acid. Hyaluronan (also called hyaluronic acid or hyaluronate) is a non-sulfated Glycosaminoglycan distributed widely throughout connective, epithelial Fusion between the sperm and oocyte plasma membranes follows, allowing the entry of the sperm nucleus, mitochondria, centriole and flagellum into the oocyte. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. A Centriole is a barrel shaped Organelle found in most animal Eukaryotic cells though absent in Higher plants and Fungi. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it The fusion is likely mediated by the protein CD9 in mice (the binding homolog). The egg "activates" once it fuses with a single sperm cell, i. 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 e. , its cell membrane changes to preventing fusion with other sperm.

This process ultimately leads to the formation of a diploid cell called a zygote. "Haplo" redirects here For the fictional character see The Death Gate Cycle. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" The zygote begins to divide and form a blastocyst and when it reaches the uterus, it performs implantation in the endometrium. The blastocyst is the structure formed in early Embryogenesis, after the formation of the Blastocoel, but before Implantation. Implantation is an event that occurs early in pregnancy in which the Embryo adheres to the wall of Uterus. At this point the female is said to be pregnant. Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female If the embryo emplants in any tissue other than the uterine wall, an ectopic pregnancy results, which can be fatal to the mother. The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the An ectopic pregnancy is a Complication of pregnancy in which the fertilized Ovum is implanted in any tissue other than the uterine wall

In some animals (e. g. rabbits) 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 fertilization

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. 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 An Gastrulation is the point in development when the implanted blastocyst develops three germ layers, the endoderm, the exoderm and the mesoderm. Gastrulation is a phase early in the development of animal Embryos during which the morphology of the embryo is dramatically restructured by Cell migration. 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 survive only until gastrulation, and have no chance of development afterward. 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. ^[3] The term "conception" is not usually used in scientific literature because of its variable definition and connotation.

Fertilisation and genetic recombination

Meiosis results in a random segregation of the genes contributed from each parent. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half 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. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete 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. A chromosome is an organized structure of DNA and Protein that is found in cells. A parent is a Father or Mother; one who sires or gives Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" 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 from the maternal parent. 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. Parthenogenesis (from the Greek παρθένος parthenos, "virgin" + γένεσις genesis, "creation" is an asexual form 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 ova of two mice, the result of which developed normally into a mouse. An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. This was achieved by blocking certain proteins that would normally prevent the possibility. ^[4][5]

See also

• Kaguya (mouse)
• Female sperm
• In vitro fertilisation
• Fetal development
• Superfetation
• Superfecundation

Notes and references