Notice that this system is the opposite of the mammalian system because in birds the female is the sex with the different sex chromosomes. The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals.
Some fish, crustaceans, insects such as butterflies and moths , and reptiles use the ZW system. More complicated chromosomal sex determining systems also exist. For example, some swordtail fish have three sex chromosomes in a population.
The sex of some other species is not determined by chromosomes, but by some aspect of the environment. Sex determination in alligators, some turtles, and tuataras, for example, is dependent on the temperature during the middle third of egg development. This is referred to as environmental sex determination, or more specifically, as temperature-dependent sex determination. In many turtles, cooler temperatures during egg incubation produce males and warm temperatures produce females, while in many other species of turtles, the reverse is true.
In some crocodiles and some turtles, moderate temperatures produce males and both warm and cool temperatures produce females. Individuals of some species change their sex during their lives, switching from one to the other.
The wrasses, a family of reef fishes, are all sequential hermaphrodites. Some of these species live in closely coordinated schools with a dominant male and a large number of smaller females. If the male dies, a female increases in size, changes sex, and becomes the new dominant male.
The fusion of a sperm and an egg is a process called fertilization. This can occur either inside internal fertilization or outside external fertilization the body of the female.
Humans provide an example of the former, whereas frog reproduction is an example of the latter. External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization takes place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male s release sperm in the same area, at the same time.
The spawning may be triggered by environmental signals, such as water temperature or the length of daylight. Nearly all fish spawn, as do crustaceans such as crabs and shrimp , mollusks such as oysters , squid, and echinoderms such as sea urchins and sea cucumbers.
Frogs, corals, mayflies, and mosquitoes also spawn Figure Internal fertilization occurs most often in terrestrial animals, although some aquatic animals also use this method. Internal fertilization may occur by the male directly depositing sperm in the female during mating. It may also occur by the male depositing sperm in the environment, usually in a protective structure, which a female picks up to deposit the sperm in her reproductive tract.
Budding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals. Budding occurs commonly in some invertebrate animals such as corals and hydras. In hydras, a bud forms that develops into an adult and breaks away from the main body, as illustrated in Figure Watch a video of a hydra budding. Fragmentation is the breaking of the body into two parts with subsequent regeneration.
If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow. For example, in many sea stars, asexual reproduction is accomplished by fragmentation. Figure Fisheries workers have been known to try to kill the sea stars eating their clam or oyster beds by cutting them in half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new half, resulting in twice as many sea stars to prey upon the oysters and clams.
Fragmentation also occurs in annelid worms, turbellarians, and poriferans. Note that in fragmentation, there is generally a noticeable difference in the size of the individuals, whereas in fission, two individuals of approximate size are formed. Parthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process and the species.
Parthenogenesis occurs in invertebrates such as water flees, rotifers, aphids, stick insects, some ants, wasps, and bees. Bees use parthenogenesis to produce haploid males drones and diploid females workers. If an egg is fertilized, a queen is produced. The queen bee controls the reproduction of the hive bees to regulate the type of bee produced.
Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Although more common in plants, parthenogenesis has been observed in animal species that were segregated by sex in terrestrial or marine zoos.
Fungal infections may prove deadly for individuals with compromised immune systems. Fungi have many commercial applications. The food industry uses yeasts in baking, brewing, and cheese and wine making. Many industrial compounds are byproducts of fungal fermentation. Fungi are the source of many commercial enzymes and antibiotics. Fungi are unicellular or multicellular thick-cell-walled heterotroph decomposers that eat decaying matter and make tangles of filaments.
Fungi are eukaryotes and have a complex cellular organization. As eukaryotes, fungal cells contain a membrane-bound nucleus where the DNA is wrapped around histone proteins. A few types of fungi have structures comparable to bacterial plasmids loops of DNA. Fungal cells also contain mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus.
Unlike plant cells, fungal cells do not have chloroplasts or chlorophyll. Many fungi display bright colors arising from other cellular pigments, ranging from red to green to black. The poisonous Amanita muscaria fly agaric is recognizable by its bright red cap with white patches. Pigments in fungi are associated with the cell wall.
They play a protective role against ultraviolet radiation and can be toxic. The poisonous Amanita muscaria : The poisonous Amanita muscaria is native to temperate and boreal regions of North America. The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans.
Chitin, also found in the exoskeleton of insects, gives structural strength to the cell walls of fungi. The wall protects the cell from desiccation and predators. Fungi have plasma membranes similar to other eukaryotes, except that the structure is stabilized by ergosterol: a steroid molecule that replaces the cholesterol found in animal cell membranes. Most members of the kingdom Fungi are nonmotile.
The vegetative body of a fungus is a unicellular or multicellular thallus. Dimorphic fungi can change from the unicellular to multicellular state depending on environmental conditions. Unicellular fungi are generally referred to as yeasts.
Example of a unicellular fungus : Candida albicans is a yeast cell and the agent of candidiasis and thrush. This organism has a similar morphology to coccus bacteria; however, yeast is a eukaryotic organism note the nucleus.
Most fungi are multicellular organisms. They display two distinct morphological stages: the vegetative and reproductive. The vegetative stage consists of a tangle of slender thread-like structures called hyphae singular, hypha , whereas the reproductive stage can be more conspicuous.
The mass of hyphae is a mycelium. It can grow on a surface, in soil or decaying material, in a liquid, or even on living tissue. Example of a mycelium of a fungus : The mycelium of the fungus Neotestudina rosati can be pathogenic to humans. The fungus enters through a cut or scrape and develops a mycetoma, a chronic subcutaneous infection.
Most fungal hyphae are divided into separate cells by endwalls called septa singular, septum a, c. In most phyla of fungi, tiny holes in the septa allow for the rapid flow of nutrients and small molecules from cell to cell along the hypha. The W appears to be essential in determining the sex of the individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects such as butterflies and moths , and reptiles use this system.
The sex of some species is not determined by genetics, but by some aspect of the environment. Sex determination in some crocodiles and turtles, for example, is often dependent on the temperature during critical periods of egg development. This is referred to as environmental sex determination or, more specifically, as temperature-dependent sex determination.
In many turtles, cooler temperatures during egg incubation produce males, while warm temperatures produce females. In some crocodiles, moderate temperatures produce males, while both warm and cool temperatures produce females.
In some species, sex is both genetic- and temperature-dependent. Individuals of some species change their sex during their lives, alternating between male and female.
Privacy Policy. Skip to main content. Animal Reproduction and Development. Search for:. Reproduction Methods. Methods of Reproducing Animal reproduction is essential to the survival of a species; it can occur through either asexual or sexual means.
Learning Objectives Describe reproduction in animals. Asexual reproduction yields genetically-identical organisms because an individual reproduces without another. In sexual reproduction, the genetic material of two individuals from the same species combines to produce genetically-different offspring; this ensures mixing of the gene pool of the species.
Organisms that reproduce through asexual reproduction tend to grow exponentially and rely on mutations for DNA variation, while those that reproduce sexually yield a smaller number of offspring, but have larger genetic variation.
Key Terms reproduction : the act of producing new individuals biologically clone : a living organism produced asexually from a single ancestor, to which it is genetically identical. Types of Sexual and Asexual Reproduction Asexual and sexual reproduction, two methods of reproduction among animals, produce offspring that are clones or genetically unique.
Learning Objectives Discuss sexual and asexual reproduction methods. Key Takeaways Key Points Asexual reproduction includes fission, budding, fragmentation, and parthenogenesis, while sexual reproduction is achieved through the combination of reproductive cells from two individuals. The ability of a species to reproduce through fragmentation depends on the size of part that breaks off, while in binary fission, an individual splits off and forms two individuals of the same size.
Budding may lead to the production of a completely new adult that forms away from the original body or may remain attached to the original body. Observed in invertebrates and some vertebrates, parthenogenesis produce offspring that may be either haploid or diploid.
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