What Are the Steps of Fertilization in Humans?
Once one sperm has fertilized the egg, it is too late for the other sperm cells. No other sperm cell can get in. Once a sperm cell fertilizes an egg cell, it becomes a zygote. The zygote (fertilized egg) at this stage possesses half the DNA (characteristics) of each of its two parents. Fertilization, union of a sperm nucleus, of paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo. In all organisms the essence of fertilization is, in fact, the fusion of the hereditary material of two different sex cells, or gametes, each of which carries half the number of chromosomes typical of the species.
From the previous page, we mentioned that the sperm cell is released into the female organ. The cells make their way through to the top of the vagina, through the cervix, and into the uterus. But they do not stay there — they continue their journey into the fallopian tube and travel upward. If there is any ovum egg cell released, the egg cell and what sports are jamaica competing in the olympics sperm cells meet.
The ovum is released by the ovaries in a process called ovulation. When they meet, there are millions of sperm cells, and they will all meet the only egg. When the sperm cells meet the egg, only the sperm cell that can break through the egg membrane wins! Then, the egg nucleus meets the sperm nucleus, and fertilization occurs.
A new life begins, and the female is pregnant now. In the diagram, notice how millions of sperm cells all trying to break through the membrane of the egg cell. Sometimes, none of the sperm cells is strong enough to break through the egg membrane.
If this happens, both male and female cells just dissolve and get washed away. Once one sperm has fertilized the egg, it is too late for the other sperm cells.
No other sperm cell can get in. Once a sperm cell fertilizes an egg cell, it becomes a zygote. The zygote fertilized egg at this what is tonic water yahoo answers possesses half the DNA characteristics of each of its two parents. The zygote then divides itself to form a very tiny ball called an embryo.
The embryo continues downwards and finds itself in a comfortable place in the uterus. There, the embryo attaches itself to the lining walls of the uterus and begins to grow there. Skip to content Reproduction.
Introduction to human reproduction. The female reproductive system. The male reproductive system. What is mating? What is fertilization? Fetus development. What is Fertilization?
Now hold on, because this is not fertilization yet!
Dec 03, · Human fertilization is defined as the union between egg and sperm cells to cause a pregnancy. In humans, fertilization is an internal process, which is to say, it takes place inside the body of females, particularly in the Fallopian tubes, hence the more specific term natural or 'in vivo' fertilization. Fertilization Fertilization, pictured in figure (a) below is the process in which gametes (an egg and sperm) fuse to form a zygote. The egg and sperm each contain one set of chromosomes. To ensure that the offspring has only one complete diploid set of chromosomes, only . May 07, · The process of fusion of a sperm with an ovum is called fertilization. During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum (FigureA.2) and induces changes in the membrane that block the entry of additional sperms. Thus,It ensures that only one sperm can fertilised an ovum.
Fertilization , union of a sperm nucleus , of paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo. In all organisms the essence of fertilization is, in fact, the fusion of the hereditary material of two different sex cells , or gametes , each of which carries half the number of chromosomes typical of the species.
The most primitive form of fertilization, found in microorganisms and protozoans, consists of an exchange of genetic material between two cells. The first significant event in fertilization is the fusion of the membranes of the two gametes, resulting in the formation of a channel that allows the passage of material from one cell to the other.
Fertilization in advanced plants is preceded by pollination , during which pollen is transferred to, and establishes contact with, the female gamete or macrospore. Fusion in advanced animals is usually followed by penetration of the egg by a single spermatozoon. The result of fertilization is a cell zygote capable of undergoing cell division to form a new individual.
The fusion of two gametes initiates several reactions in the egg. One of these causes a change in the egg membrane s , so that the attachment of and penetration by more than one spermatozoon cannot occur.
In species in which more than one spermatozoon normally enters an egg polyspermy , only one spermatozoal nucleus actually merges with the egg nucleus. The most important result of fertilization is egg activation, which allows the egg to undergo cell division.
Activation, however, does not necessarily require the intervention of a spermatozoon; during parthenogenesis , in which fertilization does not occur, activation of an egg may be accomplished through the intervention of physical and chemical agents. Invertebrates such as aphids , bees , and rotifers normally reproduce by parthenogenesis.
In plants, certain chemicals produced by the egg may attract spermatozoa. In animals, with the possible exception of some cnidarians coelenterates , it appears likely that contact between eggs and spermatozoa depends on random collisions.
On the other hand, the gelatinous coats that surround the eggs of many animals exert a trapping action on spermatozoa, thus increasing the chances for successful sperm-egg interaction.
The eggs of marine invertebrates, especially echinoderms , are classical objects for the study of fertilization. These transparent eggs are valuable for studies observing living cells and for biochemical and molecular investigations because the time of fertilization can be accurately fixed, the development of many eggs occurs at about the same rate under suitable conditions, and large quantities of the eggs are obtainable. The eggs of some teleosts and amphibians also have been used with favourable results.
Maturation is the final step in the production of functional eggs oogenesis that can associate with a spermatozoon and develop a reaction that prevents the entry of more than one spermatozoon. In addition, the cytoplasm of a mature egg can support the changes that lead to fusion of spermatozoal and egg nuclei and initiate embryonic development.
Cortical granules of sea urchin eggs, aligned beneath the plasma membrane thin, soft, pliable layer of mature eggs, have a diameter of 0. Cortical granules are formed in a cell component known as a Golgi complex , from which they migrate to the surface of the maturing egg. The surface of a sea urchin egg has the ability to affect the passage of light unequally in different directions; this property, called birefringence , is an indication that the molecules comprising the surface layers are arranged in a definite way.
Since birefringence appears as an egg matures, it is likely that the properties of a mature egg membrane are associated with specific molecular arrangements. A mature egg is able to support the formation of a zygote nucleus; i. In most eggs the process of reduction of chromosomal number meiosis is not completed prior to fertilization. In such cases the fertilizing spermatozoon remains beneath the egg surface until meiosis in the egg has been completed, after which changes and movements that lead to fusion and the formation of a zygote occur.
The surfaces of most animal eggs are surrounded by envelopes, which may be soft gelatinous coats as in echinoderms and some amphibians or thick membranes as in fishes , insects , and mammals. In order to reach the egg surface, therefore, spermatozoa must penetrate these envelopes; indeed, spermatozoa contain enzymes organic catalysts that break them down. In some cases e. The jelly coats of echinoderm and amphibian eggs consist of complex carbohydrates called sulfated mucopolysaccharides.
The envelope of a mammalian egg is more complex. The egg is surrounded by a thick coat composed of a carbohydrate protein complex called zona pellucida. The zona is surrounded by an outer envelope, the corona radiata, which is many cell layers thick and formed by follicle cells adhering to the oocyte before it leaves the ovarian follicle.
Although it once was postulated that the jelly coat of an echinoderm egg contains a substance fertilizin thought to have an important role not only in the establishment of sperm-egg interaction but also in egg activation, fertilizin now has been shown identical with jelly-coat material, rather than a substance continuously secreted from it.
Yet there is evidence that the egg envelopes do play a role in fertilization; i. Article Introduction Maturation of the egg Egg surface Egg coats Events of fertilization Sperm-egg association Specificity of sperm-egg interaction Prevention of polyspermy Formation of the fertilization membrane Formation of the zygote nucleus Biochemical analysis of fertilization Show more.
Videos Images. Additional Info. Print print Print. Table Of Contents. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login.
External Websites. Author of Chemistry and Physiology of Fertilization. See Article History. A sperm cell attempting to penetrate an egg ovum to fertilize it. The journey of a fertilized egg in a woman. In mammals, eggs are released by the ovaries.
If an egg meets a sperm cell, it may become fertilized. The fertilized egg travels to the uterus, where it grows and develops into a new individual. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Load Next Page.