AskDefine | Define conceiver

Dictionary Definition

conceiver n : someone who creates new things [syn: originator, mastermind]

Extensive Definition

For soil improvement see Fertilization (soil).
Fertilisation (also known as conception, fecundation and syngamy), is fusion of gametes to produce 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.
The entire process of development of new individuals is called procreation, the act of species reproduction.

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. 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 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. 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. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule.

Double fertilisation anchor 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 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 fertilises 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 seed.
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.
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.

Fertilisation in animals

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

Sea urchins

Chemotaxis was discovered as the method by 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.


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.
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.
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 binding homolog). Once the ovum fuses with a single sperm cell, its cell membrane changes, preventing fusion with other sperm (see Egg activation).
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.
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.


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 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. 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. 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 from the maternal parent.


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 ova 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.

Notes and references

conceiver in Bengali: নিষেকক্রিয়া
conceiver in Breton: Speriañ
conceiver in Bulgarian: Зачеване
conceiver in Catalan: Fecundació
conceiver in Czech: Oplodnění
conceiver in Danish: Befrugtning
conceiver in German: Befruchtung
conceiver in Spanish: Fecundación
conceiver in French: Fécondation
conceiver in Croatian: Oplodnja
conceiver in Indonesian: Pembuahan
conceiver in Italian: Fecondazione
conceiver in Hebrew: הפריה
conceiver in Lithuanian: Apvaisinimas
conceiver in Macedonian: Оплодување
conceiver in Dutch: Bevruchting
conceiver in Japanese: 受精
conceiver in Norwegian: Befruktning
conceiver in Polish: Zapłodnienie
conceiver in Portuguese: Fecundação
conceiver in Romanian: Fecundaţie
conceiver in Quechua: Yumay
conceiver in Russian: Половой процесс
conceiver in Simple English: Fertilization
conceiver in Slovak: Oplodnenie
conceiver in Serbian: Оплођење
conceiver in Sundanese: Fértilisasi
conceiver in Finnish: Hedelmöitys
conceiver in Swedish: Befruktning
conceiver in Turkish: Döllenme
conceiver in Ukrainian: Запліднення
conceiver in Chinese: 受精
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