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Part of a series on
Sex
Biological terms
Sexual differentiation
Sex-determination system
Sex chromosome
Hermaphrodite
Sexual reproduction
Evolution of sexual reproduction
Gametogenesis
Gamete
Fertilization
Sexual reproduction in animals
Sexuality
Human sexuality
A gamete (/ˈɡæmiːt/; from Ancient Greek γαμετή gamete from gamein 'to marry'[1]) is a haploidcell that fuses with another haploid cell during fertilization in organisms that sexually reproduce. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual that produces the larger type of gamete—called an ovum— and a male produces the smaller tadpole-like type—called a sperm. In short a gamete is an egg cell (female gamete) or a sperm (male gamete). This is an example of anisogamy or heterogamy, the condition in which females and males produce gametes of different sizes (this is the case in humans; the human ovum has approximately 100,000 times the volume of a single human sperm cell[2][3]). In contrast, isogamy is the state of gametes from both sexes being the same size and shape, and given arbitrary designators for mating type. The name gamete was introduced by the Austrian biologist Gregor Mendel. Gametes carry half the genetic information of an individual, one ploidy of each type, and are created through meiosis.
Oogenesis is the process of female gamete formation in animals. This process involves meiosis (including meiotic recombination) occurring in the diploid primary oocyte to produce the haploid ovum. Spermatogenesis is the process of male gamete formation in animals. This process also involves meiosis occurring in the diploid primary spermatocyte to produce the haploid spermatozoon.
Formation Of Gametes Human
Dissimilarity[edit]
Role Of Gamete Formation Examples
In contrast to a gamete, the diploid somatic cells of an individual contain one copy of the chromosome set from the sperm and one copy of the chromosome set from the egg cell; that is, the cells of the offspring have genes expressing characteristics of both the father and the mother. A gamete's chromosomes are not exact duplicates of either of the sets of chromosomes carried in the diploid chromosomes, and often undergo random mutations resulting in modified DNA and subsequently, new proteins and phenotypes.[citation needed]
Sex determination in humans and birds[edit]
Gamete Formation Occurs In
In humans, a normal ovum can carry only an X chromosome (of the X and Y chromosomes), whereas a sperm may carry either an X or a Y (a non-normal ovum can end up carrying two or no X chromosomes, as a result of an irregularity at either of the two stages of meiosis, while a non-normal sperm cell can end up carrying either no sex-defining chromosomes, an XY pair, or XX pair as a result of the forementioned reason); ergo the male sperm determines the sex of any resulting zygote, if the zygote has two X chromosomes it will develop into a female, if it has an X and a Y chromosome, it will develop into a male.[4] For birds, the female ovum determines the sex of the offspring, through the ZW sex-determination system.[4]
Artificial gametes[edit]
Artificial gametes, also known as In vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and In vitro generated gametes (IVG), are gametes derived from stem cells. Research shows that artificial gametes may be a reproductive technique for same-sex male couples, although a surrogate mother would still be required for the gestation period.[5] Women who have passed menopause may be able to produce eggs and bear genetically related children with artificial gametes.[5] Robert Sparrow wrote, in the Journal of Medical Ethics, that embryos derived from artificial gametes could be used to derive new gametes and this process could be repeated to create multiple human generations in the laboratory.[6] This technique could be used to create cell lines for medical applications and for studying the heredity of genetic disorders.[6] Additionally, this technique could be used for human enhancement by selectively breeding for a desired genome or by using recombinant DNA technology to create enhancements that have not arisen in nature.[6]
Plants[edit]
Plants which reproduce sexually also have gametes. However, since plants have an alternation of diploid and haploid generations some differences exist. In flowering plants the flowers use meiosis to produce a haploid generation which produce gametes through mitosis. The female haploid is called the ovule and is produced by the ovary of the flower. When mature the haploid ovule produces the female gamete which are ready for fertilization. The male haploid is pollen and is produced by the anther, when pollen lands on a mature stigma of a flower it grows a pollen tube down into the flower. The haploid pollen then produces sperm by mitosis and releases them for fertilization.
Notes and references[edit]
^'gamete'. Online Etymology Dictionary.
^Marshall, A. M. 1893. Vertebrate embryology: a text-book for students and practitioners. GP Putnam's Sons.
^Yeung, C., M. Anapolski, M. Depenbusch, M. Zitzmann, and T. Cooper. 2003. 'Human sperm volume regulation. Response to physiological changes in osmolality, channel blockers and potential sperm osmolytes.' Human Reproduction 18:1029.
^ abJay Phelan (30 April 2009). What Is Life?: A Guide to Biology W/Prep-U. Macmillan. pp. 237–. ISBN978-1-4292-2318-8. Retrieved 8 October 2010.
^ abNewson, A J; Smajdor, A C (2005). 'Artificial gametes: new paths to parenthood?'. Journal of Medical Ethics. 31: 184–186. doi:10.1136/jme.2003.004986. PMC1734101. Retrieved 26 February 2015.
^ abcSparrow, Robert (4 April 2013). 'In vitro eugenics'. Journal of Medical Ethics. doi:10.1136/medethics-2012-101200. Retrieved 8 March 2015.
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Gamete&oldid=918729306'
Gametes are reproductive cells (sex cells) that unite during sexual reproduction to form a new cell called a zygote. Male gametes are sperm and female gametes are ova (eggs). In seed-bearing plants, pollen is the male sperm producing gametophyte. Female gametes (ovules) are contained within the plant ovary. In animals, gametes are produced in male and female gonads. Sperm are motile and have a long, tail-like projection called a flagellum. However, ova are non-motile and relatively large in comparison to the male gamete.
Gamete Formation
Gametes are formed by a type of cell division called meiosis. This two-step division process produces four daughter cells that are haploid. Haploid cells contain only one set of chromosomes. When the haploid male and female gametes unite in a process called fertilization, they form what is called a zygote. The zygote is diploid and contains two sets of chromosomes.
Gamete Types
Some male and female gametes are of similar size and shape, while others are different in size and shape. In some species of algae and fungi, male and female sex cells are almost identical and both are usually motile. The union of these types of gametes is known as isogamy. In some organisms, gametes are of dissimilar size and shape. This is known as anisogamy or heterogamy (hetero-, -gamy). Higher plants, animals, as well as some species of algae and fungi, exhibit a special type of anisogamy called oogamy. In oogamy, the female gamete is non-motile and much larger than the male gamete.
Gametes and Fertilization
Fertilization occurs when male and female gametes fuse. In animal organisms, the union of sperm and egg occurs in the fallopian tubes of the female reproductive tract. Millions of sperm are released during sexual intercourse that travel from the vagina to the fallopian tubes. Sperm are specially equipped for fertilizing an egg. The head region contains a cap-like covering called an acrosome that contains enzymes which help the sperm cell penetrate the zona pellucida (outer covering of an egg cell membrane). Upon reaching the egg cell membrane, the sperm head fuses with the egg cell. Penetration of the zona pellucida triggers the release of substances that modify the zona pellucida and prevent any other sperm from fertilizing the egg. This process is crucial as fertilization by multiple sperm cells, or polyspermy produces a zygote with extra chromosomes. This condition is lethal to the zygote.
Upon fertilization, the two haploid gametes become one diploid cell or zygote. In humans, this means that the zygote will have 23 pairs of homologous chromosomes for a total of 46 chromosomes. The zygote will continue to divide by mitosis and eventually mature into a fully functioning individual. Whether or not this individual will be male or female is determined by the inheritance of sex chromosomes. A sperm cell may have one of two types of sex chromosomes, an X or Y chromosome. An egg cell only has one type of sex chromosome, an X chromosome. Should a sperm cell with a Y sex chromosome fertilize an egg, the resulting individual will be male (XY). Should a sperm cell with an X sex chromosome fertilize an egg, the resulting individual will be female (XX).