1. Gamete Formation And Fertilization
2. Gamete Formation Diagram Definition
3. Meiosis And Gamete Formation
4. Gamete Formation In Plants
5. Gamete Formation In Plants

The process by which the chromosome number is halved during gamete formation is meiosis. In meiosis, a cell containing the diploid number of chromosomes is converted into four cells, each having the haploid number of chromosomes. The process by which the chromosome number is halved during gamete formation is meiosis. In meiosis, a cell containing the diploid number of chromosomes is converted into four cells, each having the haploid number of chromosomes. In human cells, for instance, a reproductive cell containing 46 chromosomes yields four cells, each with 23 chromosomes. The male gamete, sperm, is a smaller, mobile cell that meets up with the much larger and less mobile female gamete, egg or ova. Both sperm and egg are only haploid cells. They only carry half of.

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).

Gametogenesis is a biological process by which diploid or haploidprecursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

• 1In Animals
  • 1.1Stages

In Animals[edit]

Animals produce gametes directly through meiosis in organs called gonads (testis in males and ovaries in females). Males and females of a species that reproduce sexually have different forms of gametogenesis:

• spermatogenesis (male)
• oogenesis (female)

Stages[edit]

However, before turning into gametogonia, the embryonic development of gametes is the same in males and females.

Common path[edit]

Gametogonia are usually seen as the initial stage of gametogenesis. However, gametogonia are themselves successors of primordial germ cells (PGCs) from the dorsal endoderm of the yolk sac migrate along the hindgut to the gonadal ridge. They multiply by mitosis, and, once they have reached the gonadal ridge in the late embryonic stage, are referred to as gametogonia. Once the germ cells have developed into gametogonia, they are no longer the same between males and females.

Individual path[edit]

From gametogonia, male and female gametes develop differently - males by spermatogenesis and females by oogenesis. However, by convention, the following pattern is common for both:

Gamete Formation And Fertilization

In vitro gametogenesis[edit]

In vitro gametogenesis (IVG) is the technique of developing in vitro generated gametes, i.e., 'the generation of eggs and sperm from pluripotent stem cells in a culture dish.'^[1] This technique is currently feasible in mice and will likely have future success in humans and nonhuman primates.^[1]

Gamete Formation Diagram Definition

In gametangia[edit]

Fungi, algae, and primitive plants form specialized haploid structures called gametangia, where gametes are produced through mitosis. In some fungi, such as the Zygomycota, the gametangia are single cells, situated on the ends of hyphae, which act as gametes by fusing into a zygote. More typically, gametangia are multicellular structures that differentiate into male and female organs:

Meiosis And Gamete Formation

• antheridium (male)
• archegonium (female)

In flowering plants[edit]

In angiosperms, the male gametes (always two) are produced inside the pollen tube (in 70% of the species) or inside the pollen grain (in 30% of the species) through the division of a generative cell into two sperm nuclei. Depending on the species, this can occur while the pollen forms in the anther (pollen tricellular) or after pollination and growth of the pollen tube (pollen bicellular in the anther and in the stigma). The female gamete is produced inside the embryo sac of the ovule.

Meiosis[edit]

Meiosis is a central feature of gametogenesis, but the adaptive function of meiosis is currently a matter of debate. A key event during meiosis is the pairing of homologous chromosomes and recombination (exchange of genetic information) between homologous chromosomes. This process promotes the production of increased genetic diversity among progeny and the recombinational repair of damage in the DNA to be passed on to progeny. To explain the adaptive function of meiosis (as well as of gametogenesis and the sexual cycle), some authors emphasize diversity,^[2] and others emphasize DNA repair. ^[3]

See also[edit]

References[edit]

1. ^ ^abCohen, Glenn; Daley, George Q.; Adashi, Eli Y. (January 11, 2017). 'Disruptive reproductive technologies'. Science Translational Medicine. 9 (372). doi:10.1126/scitranslmed.aag2959. Retrieved January 16, 2017. In vitro gametogenesis (IVG)—the generation of eggs and sperm from pluripotent stem cells in a culture dish. Currently feasible in mice, IVG is poised for future success in humans and promises new possibilities for the fields of reproductive and regenerative medicine.
2. ^Harrison CJ, Alvey E, Henderson IR (2010). 'Meiosis in flowering plants and other green organisms'. J. Exp. Bot. 61 (11): 2863–75. doi:10.1093/jxb/erq191. PMID20576791.
3. ^Mirzaghaderi G, Hörandl E (2016). 'The evolution of meiotic sex and its alternatives'. Proc. Biol. Sci. 283 (1838). doi:10.1098/rspb.2016.1221. PMC5031655. PMID27605505.

Notes[edit]

Gamete Formation In Plants

1. ^Sources are mixed when using this system of numbering. Some sources use the chromatid number when writing 'n' rather than the ploidy number. Hence gametogonium and primary gametocyte would be '4n' rather than '2n' with '4c' for copies. The system used below has been determined by wikipedia consensus and should not necessarily be used as the definitive source on the issue.

Gamete Formation In Plants