Sexual reproduction is a kind of life cycle where generations alternate between cells with a single set of chromosomes haploid and cells with a double set of diploid.
Diploid cells divide into haploid cells in a process called meiosis.
Two haploid cells combine into one diploid cell in a process called fertilisation. Between fertilisation and meiosis there can be a large number of cell divisions without change Unisexual reproduction wikipedia joey the number of chromosomes.
Fertilization creates a single-celled zygote which includes genetic material from both gametes. In a process called genetic recombinationgenetic material DNA joins up so that homologous chromosome sequences are aligned with each other, and
Unisexual reproduction wikipedia joey is followed by exchange of genetic information.
Two rounds of cell division then produce four daughter cells with half the number of chromosomes from each original parent cell, and the same number of chromosomes as both parents. For instance, in human reproduction each human cell contains 46 chromosomes in 23 pairs.
Meiosis in the parents' gonads produce gamete cells which only contain 23 chromosomes each.
When the gametes are combined via sexual intercourse
Unisexual reproduction wikipedia joey form a fertilized egg, the resulting child will have 23 chromosomes from each parent genetically recombined into 23 chromosome pairs or 46 total. Cell division mitosis then initiates the development of a new individual organism in multicellular organisms including animals and plantsfor the vast majority of whom this is the primary method of reproduction.
The evolution of sexual reproduction is a major puzzle because asexual reproduction should be able to outcompete it as every young organism created can bear its own Unisexual reproduction wikipedia joey. This implies that an asexual population has "Unisexual reproduction wikipedia joey" intrinsic capacity to grow more rapidly with each generation.
One definite advantage of sexual reproduction is that it prevents the accumulation of genetic mutations. Sexual selection is a mode of natural selection in which some individuals out-reproduce others of a population because they are better at securing mates for sexual reproduction. Prokaryoteswhose initial cell has additional or transformed genetic material, reproduce through asexual reproduction but may, in lateral gene transferdisplay processes such as bacterial conjugationtransformation and transductionwhich are similar to sexual reproduction although they do not lead to reproduction.
The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1 to 1. Biologists studying evolution propose several explanations for why sexual reproduction developed and why it is maintained.
These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of adaptation to changing environments dealing with competitionand masking deleterious mutations. Larger populations appear to respond more quickly to benefits obtained through Unisexual reproduction wikipedia joey reproduction than do smaller population sizes.
Maintenance of sexual reproduction has been explained by theories that work at several levels of selectionthough some of these models remain controversial. Sexual reproduction allows these species to exhibit characteristics that depend on the specific environment that they inhabit, and the particular survival strategies that they employ.
In order to sexually reproduce, both males and females need to find a mate. Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway.
Thus sexual Unisexual reproduction wikipedia joey, as a form of natural selectionhas an effect on evolution. Sexual dimorphism is where the basic phenotypic traits vary between males and Unisexual reproduction wikipedia joey of the same species.
Dimorphism is found in both sex organs and in secondary sex characteristicsbody size, physical strength and morphology, biological ornamentationbehavior and other bodily traits.
However, sexual selection is only implied over an extended period of time leading to sexual dimorphism. Apart from some eusocial waspsorganisms which reproduce sexually have a 1: The English statistician and biologist Ronald Fisher outlined why this is so in what has come to be known as Fisher's principle.
Insect species make up more than two-thirds Unisexual reproduction wikipedia joey all extant animal species. Most insect species reproduce sexually, though some species are facultatively parthenogenetic. Many insects species have sexual dimorphismwhile in others the sexes look nearly identical. Typically they have two sexes with males producing spermatozoa and females ova. The ova develop into eggs that have a covering called the chorionwhich forms before internal fertilization.
Insects have very diverse mating and reproductive strategies most often resulting in the male depositing spermatophore within the female, which she stores until she is ready for egg fertilization.
After fertilization, and the formation of a zygote, and varying degrees development, in many species the eggs are deposited outside the female; while "Unisexual reproduction wikipedia joey" others, they develop further within the female and are born live.
There are three extant kinds of mammals: In placental mammals, offspring are born as juveniles: After several months or years, depending on the species, the sex organs develop further to maturity and the animal becomes sexually mature. Most female mammals are only fertile during certain periods during their estrous cycle, at which point they are ready to mate. Individual male and female mammals meet and carry out copulation.
The vast majority of fish species lay eggs that are then by the male,  some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift or sink
Unisexual reproduction wikipedia joey the water column.
Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fish that have live-bearing offspring include the guppy and mollies or Poecilia.
Fishes that give birth to live young can be ovoviviparouswhere the eggs are fertilized within the female and the eggs simply hatch within the female body, or in seahorsesthe male carries the developing young within a pouch, and gives birth to live young.
Some fish are hermaphroditeswhere a single fish is both male and female and can produce eggs and sperm. In hermaphroditic fish, some are male and female at the same time while in other fish they are serially hermaphroditic; starting as one sex and changing to the other.
In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. Poecilia formosa mate with males of other fish species that use internal fertilization, the sperm does not the eggs but stimulates the growth of the eggs which develops into embryos.
Animals typically produce gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization follows immediately after meiosis.
Plants on "Unisexual reproduction wikipedia joey" other hand have mitosis occurring in spores, which are produced by meiosis. The spores germinate into the gametophyte phase. The gametophytes of different groups of plants vary in size; angiosperms have as few as three cells in pollen, and mosses and other so called primitive plants may have several million cells.
Plants have an alternation of generations where the sporophyte phase is succeeded by the gametophyte phase. The sporophyte phase produces spores within the sporangium by meiosis. Flowering plants are the dominant plant form on land and they reproduce either sexually or asexually. Often their most distinguishing feature is their reproductive organs, commonly called flowers.
The anther produces Unisexual reproduction wikipedia joey grains which contain the male gametophytes sperm. For pollination to occur, pollen grains must attach to the stigma of the female reproductive structure carpelwhere the female gametophytes ovules are located inside the ovary. After Unisexual reproduction wikipedia joey pollen tube grows through the carpel's style, the sex cell nuclei from the pollen grain migrate into the ovule to fertilize the egg cell and endosperm nuclei within the female gametophyte in a process termed double fertilization.
The resulting zygote develops into an embryo, while the triploid endosperm one sperm cell plus two female cells and female tissues of the ovule give rise to the surrounding tissues in the developing seed. The ovary, which the female gametophyte sthen grows into a fruitwhich surrounds the seed s.
Plants may either self-pollinate or cross-pollinate. Nonflowering plants like fernsmoss and liverworts use other means of sexual reproduction. Inflowers dating from the Cretaceous million years before present were found encased in amber, the oldest evidence of sexual reproduction in a flowering plant.
Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects. Ferns mostly produce large diploid sporophytes with rhizomesroots and leaves; and on fertile leaves called sporangiumspores are produced.
The spores are released and germinate to produce short, thin gametophytes that are typically heart shaped, small and green in color. The gametophytes or thallusproduce both motile sperm in the antheridia and egg cells in separate archegonia.
After rains or when dew deposits a film of water, the motile sperm are splashed away from the antheridia, which are normally produced on the Unisexual reproduction wikipedia joey side of the thallus, and swim in the film of water to the archegonia where they fertilize the egg.
To promote out crossing or cross fertilization the sperm are released before the eggs are receptive of the sperm, making it more likely that the sperm will fertilize the eggs of different thallus. A zygote is formed after fertilization, which grows into a new sporophytic plant.
The condition of having separate sporephyte and gametophyte plants is called alternation of generations. Other plants with similar reproductive means include the PsilotumLycopodiumSelaginella and Equisetum.
The bryophyteswhich include liverwortshornworts and mossesreproduce both sexually and vegetatively. They are small plants found growing in moist locations and like ferns, have motile sperm with flagella and need water to facilitate sexual reproduction. These Unisexual reproduction wikipedia joey start as a haploid spore that grows into the dominate form, which is a multicellular haploid body with leaf-like structures that photosynthesize.
Haploid gametes are produced in antherida and archegonia by mitosis. The sperm from the antherida respond to chemicals released by ripe archegonia and swim to them in a film of water and fertilize the egg cells thus producing a zygote.
The zygote divides by mitotic division and grows into a sporophyte that is diploid. The multicellular diploid sporophyte produces structures called spore capsules, which are connected by seta to the archegonia. The spore capsules produce spores by meiosis, when ripe the capsules burst open and
Unisexual reproduction wikipedia joey spores are released.
Bryophytes show considerable variation in their breeding structures and the above is a basic outline. Also in
Unisexual reproduction wikipedia joey species each plant is one sex while other species produce both sexes on the same plant. Fungi are classified by the methods of sexual reproduction they employ. The outcome of sexual reproduction most often is the production of resting spores that are used to survive inclement times and to spread.
There are typically three phases in the sexual reproduction of fungi: The cytoplasm of two parent cells fuse during plasmogamy and the nuclei fuse during karyogamy. New haploid gametes "Unisexual reproduction wikipedia joey" formed during meiosis and develop into spores. Three distinct processes in prokaryotes are regarded as similar to eukaryotic sex: Bacterial transformation involves the recombination of genetic material and its function is "Unisexual reproduction wikipedia joey" associated with DNA repair.
Bacterial transformation is a complex process encoded by numerous bacterial genes, and is a bacterial adaptation for DNA transfer. Sexual reproduction in Unisexual reproduction wikipedia joey single-celled eukaryotes may have evolved from bacterial transformation,  or from a similar process in archaea see below.
Cast (In order of appearance): Joey, Téa, Yugi, Bakura, Tristan, Yami, Kaiba, Bandit Keith, Kemo Date: November 08, YAMI: I activate Asexual Reproduction !. Organisms that reproduce through asexual reproduction tend to grow in number exponentially. The reproductive system or genital system is a system of sex organs within an organism which.
The 15mm (5/8 in) long newborn joey instinctively crawls and wriggles the several inches (15 cm), while clinging to fur. developmental states that lead to the creation of specialized structures for or asexual reproduction.