During sexual reproduction, the genetic material of two individuals is combined to produce genetically diverse offspring that differ from their parents. The genetic diversity of sexually produced offspring is thought to give sexually reproducing individuals greater fitness because more of their offspring may survive and reproduce in an unpredictable or changing environment.
Species that reproduce sexually and have separate sexes must maintain two different types of individuals, males and females. Only half the population females can produce the offspring, so fewer offspring will be produced when compared to asexual reproduction.
This is a disadvantage of sexual reproduction compared to asexual reproduction. Asexual reproduction occurs in prokaryotic microorganisms bacteria and archaea and in many eukaryotic, single-celled and multi-celled organisms. There are several ways that animals reproduce asexually, the details of which vary among individual species. Fission, also called binary fission, occurs in some invertebrate, multi-celled organisms.
It is in some ways analogous to the process of binary fission of single-celled prokaryotic organisms. The term fission is applied to instances in which an organism appears to split itself into two parts and, if necessary, regenerate the missing parts of each new organism.
For example, species of turbellarian flatworms commonly called the planarians, such as Dugesia dorotocephala , are able to separate their bodies into head and tail regions and then regenerate the missing half in each of the two new organisms.
Sea anemones Cnidaria , such as species of the genus Anthopleura Figure Budding occurs commonly in some invertebrate animals such as hydras and corals. In hydras, a bud forms that develops into an adult and breaks away from the main body Figure View this video to see a hydra budding.
Fragmentation is the breaking of an individual into parts followed by regeneration. If the animal is capable of fragmentation, and the parts are big enough, a separate individual will regrow from each part. Fragmentation may occur through accidental damage, damage from predators, or as a natural form of reproduction. Reproduction through fragmentation is observed in sponges, some cnidarians, turbellarians, echinoderms, and annelids. In some sea stars, a new individual can be regenerated from a broken arm and a piece of the central disc.
This sea star 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. Parthenogenesis is a form of asexual reproduction in which an egg develops into an individual without being fertilized.
The resulting offspring can be either haploid or diploid, depending on the process in the species. Parthenogenesis occurs in invertebrates such as water fleas, rotifers, aphids, stick insects, and ants, wasps, and bees. Ants, bees, and wasps use parthenogenesis to produce haploid males drones. The diploid females workers and queens are the result of a fertilized egg.
Some vertebrate animals—such as certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Parthenogenesis has been observed in species in which the sexes were separated in terrestrial or marine zoos. Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males.
It is possible that the asexual reproduction observed occurred in response to unusual circumstances and would normally not occur.
Sexual reproduction is the combination of reproductive cells from two individuals to form genetically unique offspring. The nature of the individuals that produce the two kinds of gametes can vary, having for example separate sexes or both sexes in each individual.
Sex determination, the mechanism that determines which sex an individual develops into, also can vary. They will leave the water to cross land and invade new habitats.
Many jurisdictions regulate the import and release of various types of crayfish. In , Missouri added marmorkrebs to its prohibited species list. Marmorkrebs accomplish asexual reproduction via apomixis , a process usually reserved for plants in which an organism can generate an embryo without fertilization.
While most asexual animal species have a choice and only turn to asexual reproduction when needed, the whiptail lizard belongs exclusively to the girls-only club. This celibate, all-female species begins the reproductive process with twice the number of chromosomes as its sexually reproducing relatives. Whiptails evolved from hybrids of other species and may possess two complete sets of chromosomes.
Whiptails live in the Southwest, Mexico and South America and are the only known unisexual reptile. Despite some rather compelling reasons why komodos don't make great pets, including that their saliva is usually toxic, some people do keep these giant lizards in the home.
Concerns aside, female komodos have a singular ability to lay eggs without having had sex, and these eggs will produce healthy male children. This occurs because female komodos have two different sex chromosomes -- W and Z -- that multiply on their own in the eggs. Chapman, Demian D. Dudgeon, Christine L. Watts, Phillip C. TA doi Shibata, Daisuke, et al. Lutes, A. Booth, Warren, et al. Gutekunst, Julian, et al. Warren, Wesley C. Sandrock, Christoph, and Christoph Vorburger.
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By Katherine Gallagher Katherine Gallagher. Katherine Gallagher is a writer and sustainability expert. She holds a B.
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