Sexual reproduction is characterized by processes that pass a combination of genetic material to offspring, resulting in diversity. The main two processes are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair usually cross over to achieve genetic recombination. Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. ... This article is about the general scientific term. ... For other uses, see Offspring (disambiguation). ... Genetic diversity is a characteristic of ecosystems and gene pools that describes an attribute which is commonly held to be advantageous for survival -- that there are many different versions of otherwise similar organisms. ... For the figure of speech, see meiosis (figure of speech). ... For information about chromosomes in genetic algorithms, see chromosome (genetic algorithm). ... Categories: Biology stubs ... A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. ...

The evolution of sex is a major puzzle. The first fossilized evidence of sexually reproducing organisms is from eukaryotes of the Stenian period, about 1.2 to 1 billion years ago.^[1] Sexual reproduction is the primary method of reproduction for the vast majority of visible organisms, including almost all animals and plants. Bacterial conjugation, the transfer of DNA between two bacteria, is often mistakenly confused with sexual reproduction, because the mechanics are similar. The evolution of sex is a major puzzle in modern evolutionary biology. ... For other uses, see Fossil (disambiguation). ... Domains and Kingdoms Nanobes Acytota Cytota Bacteria Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia An ericoid mycorrhizal fungus Life on Earth redirects here. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... The Stenian (from Greek stenos, narrow) is the final geologic period in the Mesoproterozoic Era and lasted from 1200 million years ago to 1000 million years ago. ... For other uses, see Animal (disambiguation). ... For other uses, see Plant (disambiguation). ... Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

A major question is why sexual reproduction persists when parthenogenesis appears in some ways to be a superior form of reproduction. Contemporary evolutionary thought proposes some explanations. It may be due to selection pressure on the clade itself—the ability for a population to radiate more rapidly due to a changing environment through sexual recombination than parthenogenesis allows. Alternatively, sexual reproduction may allow for the "ratcheting" of evolutionary speed as one clade competes with another for a limited resource. For the religious belief, see Virgin Birth of Jesus. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... A clade is a term belonging to the discipline of cladistics. ...

In the first stage of sexual reproduction, "meiosis," the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During "fertilization," haploid gametes come together to form a diploid zygote and the original number of chromosomes (2n) is restored.

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ...

Reproduction in plants

Main article: Plant sexuality

In flowering plants, the anther produces male gametophytes, the sperm is produced in pollen grains, which attach to the stigma on top of a carpel, in which the female gametophytes (inside ovules) are located. After the 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 produced the female gametophyte(s), then grows into a fruit, which surrounds the seed(s). Plants may either self-pollinate or cross-pollinate. Nonflowering plants like ferns, moss and liverworts use other means of sexual reproduction. Close-up of an Echinopsis spachiana flower, showing both carpels (only the styles and stigmas are visible) and stamens, making it a complete flower. ... Classes Magnoliopsida - Dicots Liliopsida - Monocots The flowering plants or angiosperms are the most widespread group of land plants. ... Stamens of the Amaryllis with prominent anthers carrying pollen Insects, while collecting nectar, unintentionally transfer pollen from one flower to another, bringing about pollination The stamen (from Latin stamen meaning thread of the warp) is the male organ of a flower. ... SEM image of pollen grains from a variety of common plants: sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis). ... Amaryllis style and stigmas A carpel is the outer, often visible part of the female reproductive organ of a flower; the basic unit of the gynoecium. ... This article or section does not cite its references or sources. ... For other uses, see Fruit (disambiguation). ... Self-pollination is the activity that arises when a flower has both stamen and pistils. ... Carpenter bee with pollen collected from Night-blooming cereus Pollination is an important step in the reproduction of seed plants: the transfer of pollen grains (containing the male gametes, sperm) to the plant carpel of flowering plants, the structure that contains the ovule (which in turn houses the female gamete... This article is about the group of pteridophyte plants. ... For other uses, see Moss (disambiguation). ... Orders Need to be entered Liverworts are non-vascular plants in the Class Marchantiopsida, formerly known as the Hepaticae. ...

Ferns typically produce large diploid sporophytes with rhizomes, roots and leaves; and on fertile leaves called sporangium, spores are produced. The spores are released and germinate to produce smaller gametophytes that are typically heart shaped, small and green in color. The gametophytes or thallus, produce 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 produce on the top side of the thallus, and swim in the film of water to the antheridia and fertilize the egg. To promote out crossing or cross fertilization the sperm are released before the egg is receptive of sperm, making it more likely that the sperm will fertilize the eggs of another thallus. A zygote is formed after fertilization, which grows into a new sporophytic plant. The condition of having separate sporephyte and gametophyte plants is call alternation of generations. Other plants with similar reproductive means include the Psilotum, Lycopodium, Selaginella and Equisetum. Young sporophytes of the common moss Tortula muralis. ... For other uses, see Rhizome (disambiguation). ... A sporangium (pl. ... This article or section is in need of attention from an expert on the subject. ... Thallus may mean: Thallus (tissue), an undifferentiated vegetative tissue (without specialization of function) of some non-mobile organisms, which were previously known as the thallophytes. ... Diagram of antheridium anatomy An antheridium (plural: antheridia) is a structure or organ of the gametophyte phase of certain plants producing and containing the spermatids or male gametes. ... An archegonium (pl: archegonia) (from the Greek arche = beginning and gonos = born) is a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete. ... For other meanings see Zygote (disambiguation). ... Alternation of generations is a term usually applied to the reproductive cycle of ferns and fern allies, although it is more correct to say alternation of phases of a single generation (see Sporic meiosis lifecycle). ... Species Psilotum nudum (L.) Beauvois Psilotum complanatum Sw. ... Lycopodium is a genus of clubmosses, also known as ground pines, in the family Lycopodiaceae, a family of fern-allies (see Pteridophyta). ... Selaginella A member of phylum Lycophyta, adapted for dry conditions (xerophyte). ... Species See text Equisetum is a genus of vascular plants that reproduce by spores rather than seeds. ...

Reproduction in mammals

There are three kind of mammals; Monotremes, Placentals and Marsupials, all with internal fertilisation yet do still differ from each other. In placental mammals, offspring are born as juveniles: complete animals with the sex organs present although not reproductively functional. After several months or years, the sex organs develop further to maturity and the animal becomes sexually mature. Most female mammals are only fertile during certain periods and during those times, they are said to be "in heat". At this point, the animal is ready to mate. Individual male and female mammals meet and carry out copulation. For most mammals, males and females exchange sexual partners throughout their adult lives. The placenta (Latin for cake, referencing its appearance in humans) is an ephemeral organ present in placental vertebrates, such as eutherial mammals and sharks during gestation (pregnancy). ... For other uses, see Offspring (disambiguation). ... A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; in mammals, these are: Female: Bartholins glands, cervix, clitoris, Fallopian tubes, labia, ovaries, Skenes... Sexual maturity is the age/stage when an organism can reproduce. ... Fertility is the natural capability of giving life. ... A pair of lions copulating in the Maasai Mara, Kenya. ...

The mammalian male

For more details on this topic, see Male reproductive system (human).

The male reproductive system contains two main divisions: the penis, and the testicles, the latter of which is where sperm are produced. In humans, both of these organs are outside the abdominal cavity, but they can be primarily housed within the abdomen in other animals (for instance, in dogs, the penis is internal except when mating). Having the testicles outside the abdomen best facilitates temperature regulation of the sperm, which require specific temperatures to survive. Sperm are the smaller of the two gametes and are generally very short-lived, requiring males to produce them continuously from the time of sexual maturity until death. Prior to ejaculation the produced sperm are stored in the seminal vesicle, a small gland that is located just behind the bladder.
A sperm cell is motile and swims via chemotaxis, using its flagellum to propel itself towards the ovum. This article is about human male reproductive system. ... The penis (plural penises, penes) is an external male sexual organ. ... Look up testes in Wiktionary, the free dictionary. ... The abdominal cavity is the cavity of the human body (and other animal bodies) that holds the bulk of the viscera and which is located below (or inferior to) the thoracic cavity, and above the pelvic cavity. ... Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ... Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different. ... Sexual maturity is the age/stage when an organism can reproduce. ... Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ...

The mammalian female

For more details on this topic, see Female reproductive system (human).

The female reproductive system likewise contains two main divisions: the vagina and uterus, which act as the receptacle for the sperm, and the ovaries, which produce the female's ova. All of these parts are always internal. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the fallopian tube into the uterus. The human females reproductive system. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... This article is about female reproductive anatomy. ... // For ovary as part of plants see ovary (plants) An ovary is an egg-producing reproductive organ found in female organisms. ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx) are two very fine tubes leading from the ovaries of female mammals into the uterus. ...

If, in this transit, it meets with sperm, the sperm penetrate and merge with the egg, fertilizing it. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina. A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ... Categories: Biology stubs ... Implantation is a phenomenon in prenatal development, i. ... Embryogenesis is the process by which the embryo is formed and develops. ... Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ...

The ova, which are the female sex cells, are much larger than the sperm and are normally formed with in the ovaries of the fetus before its birth. They are mostly fixed in location with in the ovary until their transit to the uterus, and contain nutrients for the later zygote and embryo. Over a regular interval, in response to hormonal signals, a process of oogenesis matures one ovum which is released and sent down the Fallopian tube. If not fertilized, this egg is flushed out of the system through menstruation in humans and other great apes and reabsorbed in other mammals in the estrus cycle. For other meanings see Zygote (disambiguation). ... For other uses, see Embryo (disambiguation). ... Oogenesis or rarely oögenesis is the creation of an ovum (egg cell). ... Menstrual cycle In the female reproductive system, the menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age females. ... Genera The hominids are the members of the biological family Hominidae (the great apes), which includes humans, chimpanzees, gorillas, and orangutans. ... The oestrus cycle (also œstrus or estrous cycle) refers to the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females (humans and great apes are the only mammals who undergo a menstrual cycle instead). ...

Gestation

Main articles: Pregnancy (mammals) and Pregnancy

Gestation, called pregnancy in humans, is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta, which is attached to the fetus' abdomen via an umbilical cord. This drain of nutrients can be quite taxing on the female, who is required to ingest slightly higher levels of calories. In addition, certain vitamins and other nutrients are required in greater quantities than normal, often creating abnormal eating habits. The length of gestation, called the gestation period, varies greatly from species to species; it is 40 weeks in humans, 56–60 in giraffes and 16 days in hamsters. This article does not cite any references or sources. ... This article is about human pregnancy in biological females. ... Mitosis divides genetic information during cell division. ... The Nutrition Facts table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts. ... The placenta (Latin for cake, referencing its appearance in humans) is an ephemeral organ present in placental vertebrates, such as eutherial mammals and sharks during gestation (pregnancy). ... The abdomen in a human and an ant. ... In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. ... A nutrient is a substance used in an organisms metabolism which must be taken in from the environment. ... The calorie is a unit of energy, in particular heat. ... Retinol (one vitamer of Vitamin A) A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. ... The Gestation period in a viviparous animal refers to the length of its pregnancy. ... Binomial name Linnaeus, 1758 Range map The giraffe (Giraffa camelopardalis) is an African even-toed ungulate mammal, the tallest of all land-living animal species. ... Genera Mesocricetus Phodopus Cricetus Cricetulus Allocricetulus Cansumys Tscherskia Hamsters are rodents belonging to the subfamily Cricetinae. ...

Birth

Main article: Childbirth

Once the fetus is sufficiently developed, chemical signals start the process of birth, which begins with contractions of the uterus and the dilation of the cervix. The fetus then descends to the cervix, where it is pushed out into the vagina, and eventually out of the female. The newborn, which is called an infant in humans, should typically begin respiration on its own shortly after birth. Not long after, the placenta is passed as well. Most mammals eat this, as it is a good source of protein and other vital nutrients needed for caring for the young. The end of the umbilical cord attached to the young’s abdomen eventually falls off on its own. Parturition redirects here. ... “Baby” redirects here. ... In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. ...

Monotremes

Monotremes, only five species of which exist, all from Australia and New Guinea, lay eggs. They have one opening for excretion and reproduction called the cloaca. They hold the eggs internally for several weeks, providing nutrients, and then lay them and cover them like birds. After less than two weeks the young hatches and crawls into its mother’s pouch, much like marsupials, where it nurses for several weeks as it grows. Families †Kollikodontidae Ornithorhynchidae Tachyglossidae †Steropodontidae Monotremes (from the Greek monos single + trema hole, referring to the cloaca) are mammals that lay eggs (Prototheria) instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). ... In most birds and reptiles, an egg (Latin ovum) is the zygote, resulting from fertilization of the ovum. ... In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, urinary, and genital tracts of certain animal species. ... For other uses, see Bird (disambiguation). ...

Marsupials

Marsupials reproduce in essentially the same manner, though their young are born at a far earlier stage of development than other mammals. After birth, marsupial joeys crawl into their mother’s pouch and attach to a teat, where they receive nourishment and finish developing into self-sufficient animals. This article is about mammals. ... A joey of Tasmanian Pademelon looking out from the mothers pouch A joey is any infant marsupial. ... A goat kid feeding on its mothers milk Teat is an alternative word for the nipple of a mammary gland, in humans referred to as a breast, from which milk is discharged. ...

Fish

The vast majority of fish species lay eggs that are then fertilized by the male,^[2] 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 in the water column. Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fishes that have live-bearing offspring include the Guppy and Mollies or Poecilia. Fishes that give birth to live young can be ovoviviparous, were the eggs are fertilized within the female and the eggs simply hatch within the female body, or they can be viviparous, were the female supplies nourishment to the internally growing offspring. Some fish are hermaphrodites, where 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.^[3] One fish species does not need sexually reproduction to produce offspring; Poecilia formosa can use parthenogenesis for reproduction, were unfertilized eggs develop into embryos that produce female offspring.^[4] For other uses, see Guppy (disambiguation). ... Species (see text) Poecilia Bloch & Schneider, 1801, is a genus of freshwater fish in family Poeciliidae of order Cyprinodontiformes. ... Ovoviviparous animals develop within eggs that remain within the mother up until they hatch or are about to. ... A viviparous animal is an animal employing vivipary, a method of reproduction in which the embryo develops inside the body of the mother from which it gains nourishment, and not from an egg. ... For the religious belief, see Virgin Birth of Jesus. ...

See also

• Asexual reproduction
• Biological reproduction
• Mating in fungi
• Operational sex ratio
• Reptile
• Sex organ
• Sexual intercourse
• Anisogamy
• Isogamy

Asexual reproduction in liverworts: a caducuous phylloid germinating Asexual reproduction is a form of reproduction which does not involve meiosis, ploidy reduction, or fertilization. ... Biological reproduction is the biological process by which new individual organisms are produced. ... Reptilia redirects here. ... A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; in mammals, these are: Female: Bartholins glands, cervix, clitoris, Fallopian tubes, labia, ovaries, Skenes... It has been suggested that Duration of sexual intercourse be merged into this article or section. ... Gametes (in Greek: γαμέτες) —also known as sex cells, or spores—are the specialized germ cells that come together during fertilization (conception) in organisms that reproduce sexually. ... A gamete is a specialized germ cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ...

References

1. ^ Orgel, Leslie E.. The Origin of Life on the Earth. Scientific American. Retrieved on 2007-01-03.
2. ^ BONY FISHES - Reproduction
3. ^ Orlando EF, Katsu Y, Miyagawa S, Iguchi T. J Mol Endocrinol. 2006 Oct;37(2):353-65. Cloning and differential expression of estrogen receptor and aromatase genes in the self-fertilizing hermaphrodite and male mangrove rivulus, Kryptolebias marmoratus. Department of Biological Sciences, Florida Atlantic University, North, Ft. Pierce, Florida 34946, USA. eorlando@fau.edu
4. ^ I. Schlupp, J. Parzefall, J. T. Epplen, M. Schartl Limia vittata as host species for the Amazon molly: no evidence for sexual reproduction Journal of Fish Biology Volume 48 Issue 4 Page 792-795, April 1996 (1996) Journal of Fish Biology 48 (4), 792–795. doi:10.1111/j.1095-8649.1996.tb01472.x

1. Pang, K. "Certificate Biology: New Mastering Basic Concepts", Hong Kong, 2004
2. Journal of Biology of Reproduction, accessed in August 2005.