We are searching data for your request:
Upon completion, a link will appear to access the found materials.
There are various Hermaphrodite animals, which can self fertilize.
So can this be called sexual reproduction because there is fusion of gametes though from the same individual ? Or asexual because the involvement of a single parent(characteristics of asexual reproduction)?
There is a similar question- Can Self-Fertilization in flowers be called asexual reproduction?
Can I extend the same logic mentioned in the @Hawkeye's answer to the given question link on the animal case above and say that it is a case of sexual reproduction?
Patterns of Reproduction in Animals | Essay | Reproduction | Biology
Two basic patterns of reproduction have been observed among animals and these are asexual and sexual. In asexual reproduction an individual can give rise to daughter individuals by mitotic divisions of a part of its own body no gametes are required.
In sexual reproduction, genetically distinct two special sex cell called gametes, fuse to form one cell structure the zygote which inturn divides repeatedly to grow into a fully developed new individual. The gametes, male and female differ from each other due to the presence of sex chromosomes of different nature.
The male gamete is usually small in size, motile and contains a very little cytoplasm and stored food, while female gamete is large in size, immobile and contains massive cytoplasm and stored food materials. Each of the two gametes frequently comes from a different parent so that sexual reproduction requires the participation of two parents. Single organism can also form two types of gametes that undergo fusion.
Such an organism that produces both types of gametes is called hermaphrodite. In most hermaphrodites, the two gametes do not mature at the same time, so that self-fertilization does not usually occur, cross-fertilization is common. In brief, sexual reproduction is often biparental but may also be uniparental depending on the species.
The development of an egg cell into a new individual without the participation of sperm cell from the opposite sex is called the parthenogenesis. It is a naturally occurring phenomenon among insects, crustaceans, rotifers and some platyhelminthes. It does not involve the fusion of two gametes. Parthenogenesis is rare in the vertebrates. A breed of white turkeys were found to lay eggs which would hatch without fertilization.
Gynogenesis and Androgenesis:
In gynogenesis, the development of a new individual takes place from the egg which is activated by spermatozoan but spermatozoan does not contribute any genetic material to the egg. The resulting embryo carries only maternal chromosomes. The best examples in which gynogenesis is common are Poecilia, a fish and Ptinus, a latro beetle.
Androgenesis, is the reverse condition of gynogenesis. When chromosome contribution in the developing egg comes exclusively from the male it is called androgenesis. Androgenesis in animals is known only experimentally, naturally occurring androgenesis has not been reported so- far.
In all multicellular animals it consists of the union of two dissimilar gametes, an egg nucleus with a sperm nucleus-to produce a single called diploid zygote which ultimately develops into a multicellular organism resembling the parents.
The organs which produce the gametes are called the gonads. The gonads which produce sperm cells are called the testes, while which produce egg cells are called the ovaries. Sexual reproduction involves two most fundamental events, meiosis and fertilization.
Meiosis is the means by which gametes from the germinal epithelium of the gonads are formed and reassortment of different genes takes place in the formation of gametes. Fertilization involves the fusion of two dissimilar genes in the production of offsprings.
Almost all species of animals have some methods of sexual reproduction as:
i. External Fertilization:
Most animals produce sperms and eggs but in many aquatic species these gametes unite in water there is no union between opposite sexes. This is called external fertilization.
ii. Internal Fertilization:
In all land animals the fertilization is internal. The two opposite sexes of the same species undergo copulation, whereby the sperms can be transferred to the body of the female where fertilization takes place. Many aquatic animals also have this process.
iii. Embryonic Development:
Those animals which lay eggs are said to have oviparous reproduction. In such cases the major part of embryonic development takes place outside the female body, even though fertilization has been internal. Those animals which give birth directly to the fully developed young ones are said to have viviparous reproduction.
There is a third type of reproduction known as ovoviviparous reproduction where there is a large egg which furnishes food for the developing embryo but due to internal fertilization egg remains in the females until it hatches. Thus, the young ones are born duly developed and active but they have not derived nourishment from their mother during embryonic development.
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 18.1.1), will divide along the oral-aboral axis, and sea cucumbers (Echinodermata) of the genus Holothuria, will divide into two halves across the oral-aboral axis and regenerate the other half in each of the resulting individuals.
Figure 18.1.1: The Anthopleura artemisia sea anemone can reproduce through fission.
Budding is a form of asexual reproduction that results from the outgrowth of a part of the body leading to a separation of the &ldquobud&rdquo from the original organism and the formation of two individuals, one smaller than the other. 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 18.2.2).
Figure 18.1.2: (a) Hydra reproduce asexually through budding: a bud forms on the tubular body of an adult hydra, develops a mouth and tentacles, and then detaches from its parent. The new hydra is fully developed and will find its own location for attachment. (b) Some coral, such as the Lophelia pertusa shown here, can reproduce through budding. (credit b: modification of work by Ed Bowlby, NOAA/Olympic Coast NMS NOAA/OAR/Office of Ocean Exploration)
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 18.1.3) is in the process of growing a complete sea star from an arm that has been cut off. 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.
Figure 18.1.3: (a) Linckia multifora is a species of sea star that can reproduce asexually via fragmentation. In this process, (b) an arm that has been shed grows into a new sea star. (credit a: modifiction of work by Dwayne Meadows, NOAA/NMFS/OPR)
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&mdashsuch as certain reptiles, amphibians, and fish&mdashalso 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.
Budding is a form of asexual reproduction that results from the outgrowth of a part of the body leading to a separation of the “bud” from the original organism and the formation of two individuals, one smaller than the other. 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 2]).
Figure 2: (a) Hydra reproduce asexually through budding: a bud forms on the tubular body of an adult hydra, develops a mouth and tentacles, and then detaches from its parent. The new hydra is fully developed and will find its own location for attachment. (b) Some coral, such as the Lophelia pertusa shown here, can reproduce through budding. (credit b: modification of work by Ed Bowlby, NOAA/Olympic Coast NMS NOAA/OAR/Office of Ocean Exploration)
View this video to see a hydra budding.
Evolutionary advantages of hermaphroditism:
Simultaneous hermaphrodites, such as tapeworms, have very fewer chances to meet the other counterpart s they complete their life cycle on more than one post. Thus, hermaphroditism allows it to fertilize the eggs of its own and reproduce. In sequential hermaphrodites including the clownfish, all the offspring are males. The largest male fish in the group act as a female and if it is removed, then the second-largest male fish of the group would become functional and thus, act as male or female at different times. It is also seen that siblings of one group are all males or females at the same time, which reduces the chances of inbreeding that is mating within the same group.
What is Parthenogenesis
Parthenogenesis is a reproductive mechanism in which an offspring develops from unfertilized eggs. It commonly occurs in invertebrates such as bees, wasps, ants, aphids, rotifers, etc. and lower plants. It is rare in higher animals. Parthenogenesis in plants is also called apomixis.
Figure 1: Parthenogenesis in Water Flea
The embryo produced in parthenogenesis is mostly haploid since it develops from an unfertilized egg. Sometimes, a diploid embryo is produced due to the pairing of two chromosome sets. On the other hand, the offspring can be obligate that is, it is incapable of sexual reproduction. Or else, it can be facultative and switch between sexual reproduction and parthenogenesis.
Asexual and Sexual Reproduction in Animals (With Diagram)
Useful notes on Asexual Reproduction and Sexual Reproduction are described below:
There is a large diversity among animals. There are about 1.2 million types of animals.
The lower animals like protozoans, sponges and few coelenterates reproduce in one simple way while all the rest follow a different pattern of reproduction.
Based on whether there is participation of one organism or two in the process of reproduction, there are two types of reproduction.
When offspring is produced by a single parent with or without involvement of gamete formation, the type of reproduction is sexual. When two parents (of opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction.
1. Asexual Reproduction:
In this type of reproduction neither the sex cells (nor gametes) are formed nor do they unite to form the zygote. Moreover, the participation of two organisms (male and female) is not required, only one organism reproduces. During asexual reproduction the body (somatic) cells divide, their nucleus divides either by mitosis or amitosis, therefore, such type of reproduction is also known as somatogenic or blastogenic reproduction. The asexual reproduction is commonly found in lower animals such as protozoans, sponges, coelenterates, certain worms and tunicates.
Principal forms of asexual reproduction are:
1. Binary Fission:
This is the simplest and most common method of asexual reproduction seen in unicellular organisms. This occurs under the favourable conditions of the environment. After the organism grown to its full size, the parent divides into two daughter cells which are genetically and morphologically similar. During this process, the nucleus divides into two, followed by the division of the cytoplasm.
According to the plane of division, following types of binary fission have been recognized in the organisms:
(a) Simple Binary Fission:
This type of binary fission occurs in the irregular-shaped organisms such as Amoeba in which the plane of division is difficult to ascertain (Fig. 3(A).1).
(b) Transverse Binary Fission:
If the plane of division is at right angle to the long axis of the animal, it is known as transverse binary fission as in Paramecium and Planaria (Fig. 3(A).2).
(c) Longitudinal Binary Fission:
In this type the plane of fission is parallel to the long axis, as in Euglena, Vorticella and in some corals (Fig. 3(A).3).
During binary fission the organelles of parent body either divide equally between two daughter individuals or one daughter individual retain them and other must develop new organelles.
2. Multiple Fission:
In multiple fissions the parent nucleus undergoes repeated divisions to form a large number of daughter nuclei. This is followed by the division of the cytoplasm into as many parts as there are nuclei, each part enclosing one nucleus. As a result a number of daughter cells are formed from a single parent cell at the same time. This process usually takes place under unfavorable environmental conditions. The multiple fissions occur in most algae, fungi and some protozoans, e.g., Amoeba, Plasmodium (malaria parasite) and Monocytes etc. (Fig. 3(A).4).
3. Gemmule in Sponges or Gemmulation:
Asexual reproduction occurs in sponges in various ways the best known method is gemmulation. In freshwater sponges and a few marine sponges buds are formed within the parent body and are called gemmules. These are also called as endogenous buds or internal buds.
Gemmulation begins when a small group of cells (mostly archaeocytes) become ladden with reserve food granules and become isolated at the internal surface of a sponge. Bach one mass is covered over by a protective covering and is called as a geinmule. The gemmules are expelled from the adult sponge and this is a normal reproductive process in some marine sponges.
Sometimes, gemmule formation is a means to tide over unfavourable conditions. After degeneration of the parent sponge due to drought or temperature extremes, the gemmules are liberated and germinate to adult sponge.
The freshwater sponges under family spongillidae undergo a slight different form of gemmulation. Here the gemmules consist of mass of archaeocytes ladden with reserve food materials and, in addition, they are surrounded by protective membranes formed by the archaeocyte cells. The protective covering is generally reinforced by spicules, the skeletal materials of sponges. The gemmules of freshwater sponges allow a species to survive in unfavourable conditions. In cold regions, gemmulation occurs in winter and the inactive gemmules hibernate.
In warm regions, gemmulation occurs in summer and the gemmules are said to estivate. In next spring or autumn, as the case may be, when favourable conditions return, the gemmules germinate. Their archaeocytes emerge through an opening called micropyle. The various cellular types differentiate and a new sponge grows.
4. Budding in Hydra:
During the process of bud formation or budding an outgrowth or bud appears on the parent body. The bud may be unicellular as in some protozoans (suctoria) or multicellular as in certain lower metazoans like, Sycon (sponge), Hydra (Goelenterate), Planaria (flatworm), Syllis (annelid) etc.
One or more such buds may be produced from a single parent body. The bud, which is much smaller than the parent develops to its full size either after detachment from the parent or prior to detachment being attached to its parent body. Budding may be external or exogenous as in Hydra (Fig. 3(A).5) or internal or endogenous as in Acinata.
In Hydra the external bud develops as a conical outgrowth from the body wall by the accumulation of intcrsitial cells. The bud gradually develops tentacles around the mouth, coelenteron and later separated lion) its parent by developing a constriction at its base.
When the body of Hydra or Planaria is cut into several fragments, each fragment develops into a new individual. This process is known as fragmentation. Regeneration is a process by which organisms develop or regenerate their lost or worn-out parts. Regeneration is highly developed in lower animals like protozoans, sponges, coelenterates, planarians, echinoderms etc.
Advantages of Asexual Reproduction:
1. A large number of individuals are produced within a short period from a single parent.
2. The offspring’s are genetically identical to the parent.
3. It occurs only through simple mitotic division.
4. It helps in dispersal of young ones to far off places.
5. It also helps the animal to tide over unfavourable environmental conditions.
Disadvantages of Asexual Reproduction:
1. Continuous binary fission for several generations makes the daughter individuals genetically weak and requires rejuvenation.
2. Animals produced by asexual reproduction are generally less adaptable to changing environmental conditions.
3. Since the genetic constitution of the daughter individuals is similar to the parent there is no genetic variation in the offspring’s and hence does not contribute to speciation.
2. Sexual Reproduction:
Sexual reproduction is commonly found in the complex, multicellular organisms. It involves the union of male and female sex cells or gametes to form the zygote which grow into a new individual. Two different sexes (male and female) take part in the process. The testes in male produce male gametes or sperms and the ovaries in female produce female gametes or ova.
Both these sex organs may be present in the same body. Such animals are known as bisexual or hermaphrodite animals, e.g. earthworm. Formation of sperms and ova involves meiosis or reduction division during which haploid gametes are formed from the diploid cells. Gametes vary in shapes and sizes in different animals.
Fusion of male and female gamete is known as fertilization. During fertilization a haploid (n), motile male gamete or sperm fuses with a non- motile, haploid (n) female gamete or ovum to form a diploid (2n) zygote which gives rise to a new individual (Fig. 3(A).6).
Therefore, the fusion of gametes maintains the diploid chromosome number of the organism. The fertilization may occur outside the body (external fertilization) as in frog or inside the body (internal fertilization) as in man.
Advantages of Sexual Reproduction:
1. The offspring’s produced due to sexual reproduction adapt themselves successfully to the changing environmental conditions.
2. Formation of gametes by meiosis and their fusion during fertilization produce reshuffling of genes and variation in the offspring’s. Variations in the offspring’s help them in natural selection and evolution.
Mammalian sex is determined genetically by the combination of X and Y chromosomes. Individuals homozygous for X (XX) are female and heterozygous individuals (XY) are male. In mammals, the presence of a Y chromosome causes the development of male characteristics and its absence results in female characteristics. The XY system is also found in some insects and plants.
Bird sex determination is dependent on the combination of Z and W chromosomes. Homozygous for Z (ZZ) results in a male and heterozygous (ZW) results in a female. 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. If the individual is female first, it is termed protogyny or “first female,” if it is male first, it is termed protandry or “first male.” Oysters are born male, grow in size, and become female and lay eggs. 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.
Difference between organisms that asexually reproduce and hermaphrodites [Biology]
It's my understanding that many multicellular organisms manage to reproduce in slightly unusual ways.
I have heard that shellfish have both male and female gonads. They can fertilize other species, but they can also fertilize themselves if they are too remote from other species to encounter sperm.
I have also heard there is a type of lizard which is capable of sexually reproducing and they have distinct genders: males with male gonads, females with female gonads. But without a mate the female can "clone" her DNA into an offspring that has no genetic differences from herself except for whatever genetic mutations occur in the formation of an embryo.
I have also heard that some fish are capable of spontaneously altering their gonads between male and female to whatever is most effective for even reproduction at that time. Does this mean that these fish effectively have both egg and sperm sacs? Could it/would it somehow be able to fertilize this fishes embryos with its own sperm and produce clones?
Trees have both male and female gonads. Can they reproduce with themselves? Are seeds which are unfertilized incapable of producing new saplings?
When an organism reproduces sexually it produces cells called gametes through the process of meiosis. These cells are not genetically identical to the parental organism because meiosis involves the process of recombination, which mixes DNA between different copies of a cell's chromosomes. Some organisms can have sex with themselves by joining two of their own gametes together, but this will not produce individuals genetically identical to their parents because the gametes have undergone recombination. So the offspring of self-fertilized organisms can look different form each other and from their parent, though in practice they often look very similar to their parent.
Asexual reproduction can occur in many different ways, but never involves eggs* or sperm. When a multicellular organism reproduces by physical separation, such as growing a new plant from a cutting taken from a mature plant, this is a form of asexual reproduction called vegetative propagation. When asexual offspring are produced from the same tissue that typical produces sexual offspring it is called parthenogenesis (in animals) or apomixis (in plants). We distinguish between vegetative asexual reproduction and parthenogenetic asexual reproduction because many plants can only reproduce asexually by vegetative reproduction, and to produce seeds they must use sexual reproduction.
Sexual reproduction by self-fertilization.
Asexual reproduction by parthenogenesis.
If the fish produce both kinds of gametes simultaneously they may be able to self-fertilize, but the fish that I am familiar with have to cross-fertilize. Either way no asexual offspring are made.
May trees are self compatible, but many monecious (which is just hermaphroditic for plants) trees are self incompatible, meaning that the pollen cannot fertilize an ovule of the same tree. Seeds which are unfertilized are incapable of growing unless the seed has been produced asexually, in which case the ovary never made any ova which could be fertilized.
Hope that clears some things up.
*Well, I guess the pivital moment of sex is really the union of eggs and sperm, so I would still say that a sperm is produced asexually. This matters because in many organisms (moss and ferns being the most well known examples) the hapliod gemete (sperm/egg) can grow into large organisms in their own right without being joined to another gemete. Sorry about being confusing.
Limitations of True Breeding
True breeding comes with a number of limitations, most of which stem from a lack of genetic variation. Many true breeding specimens are susceptible to disease and can suffer from a number of crippling illnesses as they grow older including bone and blood disorders. In addition, many traits may appear to breed true, such the temperament for being good guard dogs, but any characteristic that is multi-genic or influenced by the environment can show variation.