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Asexual Reproduction Genetic Variation

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Last Updated: 02 July 2021

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General | Latest Info

Typically, when we consider genetic transfer, we think of vertical gene transfer, transmission of genetic information from generation to generation. Vertical gene transfer is by far the main mode of transmission of genetic information in all cells. In sexually reproducing organisms, crossing - over events and independent assortment of individual chromosomes during meiosis contribute to genetic diversity in population. Genetic diversity is also introduced during sexual reproduction, when genetic information from two parents, each with different complements of genetic information, are combine, producing new combinations of parental genotypes in diploid offspring. The occurrence of mutations also contributes to genetic diversity in the population. Genetic diversity of offspring is useful in changing or inconsistent environments and may be one reason for evolutionary success of sexual reproduction. When prokaryotes and eukaryotes reproduce asexually, they transfer nearly identical copies of their genetic material to their offspring through vertical gene transfer. Although asexual reproduction produces more offspring more quickly, any benefits of diversity among those offspring are lose. How then do organisms whose dominant reproductive mode is asexual create genetic diversity? In prokaryotes, horizontal gene transfer, introduction of genetic material from one organism to another organism within the same generation, is an important way to introduce genetic diversity. Hgt allows even distantly related species to share genes, influencing their phenotypes. It is thought that HGT is more prevalent in prokaryotes but that only a small fraction of prokaryotic genome may be transferred by this type of transfer at any one time. As the phenomenon is investigated more thoroughly, it may be revealed to be even more common. Many scientists believe that HGT and mutation are significant sources of genetic variation, raw material for the process of natural selection, in prokaryotes. Although HGT is more common among evolutionarily related organisms, it may occur between any two species that live together in natural community. Hgt in prokaryotes is known to occur by three primary mechanisms that are illustrated in Figure 1: transformation: naked DNA is taken up from the environment. Transduction: genes are transferred between cells in virus conjugation: use of hollow tube called conjugation pilus to transfer genes between cells

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Transduction

Prokaryotes such as bacteria do have a sex life. Most prokaryotic species dont participate in sexual reproduction and have only one copy of each gene on their single lonely chromosome. Sexually reproducing organisms have two sets of chromosomes, one set from each parent, and therefore have two versions of each gene. This arrangement increases genetic diversity. However, bacteria have found ways to increase their genetic diversity through three recombination techniques: transduction, transformation and conjugation. Transduction is the transfer of DNA from one bacterium to another through action of viruses. When a virus infects a bacterium, it injects its genetic material into its victim and highjacks bacterium machinery for synthesizing DNA, RNA and proteins. Sometimes, viral genetic material joins with hosts DNA. Later, viral DNA excises itself from bacterium chromosome,s but the process is imprecise and bacterial genes might be included with newly free viral DNA. Virus cause hosts to replicate many copies of the virus genome along with any host genes along for ride. Virus then cause cells to rupture, releasing new virus particles that repeat the cycle. In this way, genes from one host combine with those of another host, perhaps from another species.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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Clinical Focus: Travis, Part 3

D. Pulicaria are small planktonic Cladocera that reproduce by cyclical parthenogenesis; ie., Individuals can reproduce both sexually and asexually. Populations reproduce asexually for extended periods ranging from weeks to years before engaging in a bout of sex, often in response to changing or deteriorating environmental conditions. One or two sexually produced eggs are deposited in a desiccation - resistant capsule, know as ephippium, formed by modification of carapace. Ephippia are readily identifiable, allowing sexually reproducing females to be easily distinguished from those reproducing asexually. Once released from female, eggs within ephippium can remain dormant until receiving suitable hatching cues. We sampled four Lake populations of D. Pulicaria from Barry County in southern Michigan, chosen because of their dramatic and consistent differences in incidence of sexual reproduction. The difference in frequency of sex is believed to be due to ecological factors influencing the ability of animals to persist in water column year - round. These populations are described in detail elsewhere, but briefly they are as follow: Little Long Lake, with 15 - 30% of the population reproducing sexually each year; Bristol Lake and Warner Lake, with 3 - 10% reproducing sexually every year; and Baker Lake, which reproduce asexually for multiple years before engaging in sexual reproduction. Each Lake population was sampled during peak sexual periods by making 20 - 30 vertical tows of standard plankton net across multiple locations in each Lake. Collect individuals were sorted in laboratory and 1000 ephippial females were isolated from each population into individual beakers. Once ephippium was released from the female, it was placed under conditions to induce hatching: 14 hr light at 10: 10 hr dark at 7, with periodic placement at 4 dark to stimulate development. One of the strengths of the Daphnia system is that all wild - collect females and hatched individuals can be maintained via clonal reproduction in individual beakers in the laboratory until sufficient numbers of family pairs are available. Each hatching sample was initiated with 10 - fold more ephippia than needed so that parent - offspring pairs for final assay could be randomly chosen from larger sample. When both eggs from ephippium hatch, one offspring was chosen randomly for assay. This does not completely remove the possibility of within - lab or within - family selection, as some ephippia do not hatch and some hatch offspring die, but if any selective effect on particular parent - offspring genetic combinations systematically influences changes in trait means or genetic variances, it most likely would have led to loss of offspring with low fitness resulting in downwardly bias estimates of changes in means and variances. For each population, life - history assay begins when 100 parent - offspring pairs have firmly establish. On average time from sampling population to initiating assay was 2. 5 months. Life - history assays were performed for each of four populations separately, but parents and offspring within each population were assayed simultaneously. Detailed descriptions of standard life - history assays are given elsewhere.

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Introduction

Many higher organisms have both sexual and asexual means of letting themselves be represented by future generations. In plants, partial asexuality is normally due to a mixture of sexual reproduction by seed and asexual reproduction by specialized structures such as runners or bulbils, whereas in animals, partial asexuality often follows from failure of cyclical parthenogens to go through the sexual stage successfully. The present article considers pattern of selectively neutral genetic variation expected in organisms with stable mixture of sexual and asexual reproduction. Asexuality has classically been regarded as a factor that reduces genetic variation. As general notion, this is, of course, not correct. Asexual species often harbour a wealth of variation coming from new mutations as well as remnant sexuality and / or multiple origins. But how genetically variable do we expect predominantly asexual organism to be? From models of infinitely large populations is know, that asexuality as such does not affect equilibrium genotype frequencies of neutral alleles in organisms practicing at least some outbreeding sexuality. The only role asexuality plays in such reproductively mixed conditions is to slow down the rates at which multilocus equilibrium values are attain. Asexuality differs in this respect from, say, inbreeding, in that it does not change the genetic structure of the population in any specific, unidirectional way. Although this insight is valuable, one can ask how relevant it is for actual populations of limited size in which genetic drift cannot be ignore. Two immediate questions arise for such populations. The first concerns the degree of allelic variation expected at loci at which neutral mutations occur. Affects this variation in two different ways. On one hand, asexuality implies that sampling drift acts at the level of individuals as well as on the level of genes, which will lead to increased homogenization at population level. On the other hand, asexuallity tends to lock up gene combinations in fixed pairs that are inherited together, which will tend to increase divergence between gene copies. By use of the coalescence argument in Model 1 below, I show how these processes interact and describe the expected pattern of pairwise allelic divergence in a population with a fixed degree of asexuality. Results are obtained under the assumption that the investigated population is large and that it has had constant size for a long time. The second question concerns genotypic variation. With the advent of methods for multilocus genotyping, genotypic, clonal, variation in populations of organisms with different degrees of asexuality has become easy to investigate empirically. It has then been found that apparently asexual organisms often harbour considerable genotypic variability. To assess the basis for this variation - is it because of low levels of sexuality or of factors such as somatic mutations, balancing selection, or perpetual recreation of asexual form? - Expect level of neutral genotypic variation in a limited population with partial asexuality must be known for comparison.

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Materials and methods

Animals produce offspring through asexual and / or sexual reproduction. Both methods have advantages and disadvantages. Asexual reproduction produces offspring that are genetically identical to their parents because offspring are all clones of original parent. A single individual can produce offspring asexually and large numbers of offspring can be produced quickly. In a stable or predictable environment, asexual reproduction IS an effective means of reproduction because all offspring will adapt to that environment. In unstable or unpredictable environment, asexually - reproducing species may be at a disadvantage because all offspring are genetically identical and may not have genetic variation to survive in new or different conditions. On the other hand, rapid rates of asexual reproduction may allow for speedy response to environmental changes if individuals have mutations. An additional advantage of asexual reproduction IS that colonization of new habitats may be easier when individuals do not need to find mate to reproduce. During sexual reproduction, 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 species a better chance of surviving in unpredictable or changing environment. Species that reproduce sexually must maintain two different types of individuals, males and females, which can limit their ability to colonize new habitats as both sexes must be present.


Asexual Reproduction

Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of species have similar vulnerabilities. Organisms that reproduce sexually yield smaller number of offspring, but large amount of variation in their genes makes them less susceptible to disease. Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, and some species of starfish are examples of animal species with this ability. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival, such as abundant food supply, adequate shelter, favorable climate, disease, optimum pH, or proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of rich supply resources. When food sources have been deplete, climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensure mixing of gene pool of species. Variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. In addition, sexual reproduction usually results in the formation of a life stage that is able to endure conditions that threaten offspring of asexual parent.S Thus, seeds, spores, eggs, pupae, cysts, or other over - wintering stages of sexual reproduction ensure survival during unfavorable times as organism can wait out adverse situations until swing back to suitability occurs.

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Discussion

Observation of C. Tuberosus nests indicates that nests are head by single pairs of primary reproductives or by neotenic reproductives together with one or both primary reproductives. Comparison of F - statistics and relatedness coefficients under several simulated breeding systems with coefficients estimated for C. Tuberosus indicate that nests are initiated by single pair of outbred primary reproductives, and for nests in which mating occurs among primary king and multiple neotenics, neotenics descend from the primary queen. The lack of isolation by distance among nests suggests that new nests are initiated by winged queens and kings after large dispersal flights. Moreover, C. Tuberosus displays genetic differentiation among nests within sample sites and between regions, but not between sites. This suggests that primary reproductives of C. Tuberosus may disperse largely at distances greater than distances separating sample sites. For instance, Macrotermes michaelseni populations show low values of genetic differentiation across large spatial scale so that populations may be regarded as panmictic on spatial scales of 25 - 50 km. Our results demonstrate the common occurrence of AQS in C. Tuberosus. With recent observations on E. Neotenicus, presence of AQS as queen replacement strategy in Termitidae is firmly establish. Far from being restricted to temperate wood - feeding Rhinotermitidae of genus Reticulitermes, AQS now involves two species which are tropical rainforest soil feeders and represent distinct subfamilies of higher termites. In AQS systems, two contrast dispersal and reproductive patterns occur simultaneously: sexually produced alates initiate new colonies after long - distance dispersal, while asexually produced neotenics reproduce inside the mother - nest. These co - occurring patterns could be seen as resulting from different selective pressures on one single genome. High dispersal abilities should be counter - select after successful colonization of the new environment because individuals that continue to disperse widely will almost certainly be unsuccessful and thus be removed from the newly colonized environment, whereas non - dispersers remain in local deme. On the other hand, sexual reproduction enhances genetic variation among sexually produced offspring that are more able to adapt to new or changing environmental conditions, whereas clonal reproduction may have short - term benefits to exploit stable environments. Queen replacement in C. Tuberosus is not accidental: queen often goes missing while the primary king remains alive and active, and parthenogenetic production of female neotenics constitutes evidence that the queen anticipates her succession. Parthenogenetic nymphs were indeed almost systematically present with physiologically reproductive primary queens. However, dynamics of AQS in C. Tuberosus present two singularities: first, primary queens were found more frequently than neotenics in field - collected colonies, including in mature ones; second, all neotenics of C. Tuberosus were small and non - physogastric. These features contrast with AQS in Reticulitermes spp. And E. Neotenicus, whose queens appear to be systematically replaced early in the colony's life by neotenics which soon become highly physogastric.


Asexual Reproduction

Asexual reproduction involves a single parent.S It results in offspring that are genetically identical to each other and to their parent. All prokaryotes and some eukaryotes reproduce this way. There are several different methods of asexual reproduction. They include binary fission, fragmentation, and budding. Binary Fission occurs when the parent cell splits into two identical daughter cells of the same size. Fragmentation occurs when the parent organism breaks into fragments, or pieces, and each fragment develops into a new organism. Starfish, like the one in the figure below, reproduce this way. New starfish can develop from single ray, or arm. Starfish, however, are also capable of sexual reproduction. Budding occurs when the parent cell forms a bubble - like bud. Bud stays attached to the parent cell while it grows and develops. When bud is fully develop, it breaks away from the parent cell and forms a new organism. Budding in yeast is shown in the figure below. Binary Fission in various single - celled organisms. Cell division is a relatively simple process in many single - celled organisms. Eventually, parent cell will pinch apart to form two identical daughter cells. In multiple Fission, multinucleated cells can divide to form more than one daughter cell. Multiple Fission is more often observed among protists. Starfish reproduce by fragmentation and yeast reproduce by budding. Both are types of asexual reproduction. Asexual reproduction can be very rapid. This is an advantage for many organisms. It allows them to crowd out other organisms that reproduce more slowly. Bacteria, for example, may be divided several times per hour. Under ideal conditions, 100 bacteria can divide to produce millions of bacterial cells in just a few hours! However, most bacteria do not live under ideal conditions. If they do, entire surface of the planet would soon be covered with them. Instead, their reproduction is kept in check by limited resources, predators, and their own wastes. This is true of most other organisms as well.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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Crossing Over

Early on in the process of meiosis, homologous chromosomes pair up and exchange parts with each other. This process is called crossing over. Each human cell contains 46 chromosomes in form of 23 pairs of homologous chromosomes. Half of each pair comes from mom and half from dad. Homologous chromosomes have the same genes in the same location, and only pair with each other. Each chromosome in pair can have the same genes or slightly different forms of the same gene. They line up side - by - side and break off pieces of themselves and trade those pieces with each other. Crossing over is the first way that genes are shuffled in sexual reproduction to produce genetic diversity.

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Gamete Fusion

Genetic diversity of sexual reproduction, observed in most eukaryotes, is thought to give species better chances of survival. Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. During sexual reproduction, genetic material of two individuals is combined to produce genetically - diverse offspring that differ from their parents. The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success. In many animals, it is actually the only mode of reproduction. Genetic diversity of sexually - produced offspring is thought to give species a better chance of surviving in unpredictable or changing environment. Scientists recognize some real disadvantages to sexual reproduction. On the surface, creating offspring that are genetic clones of parents appears to be a better system. If the parent organism is successfully occupying habitat, offspring with the same traits would be similarly successful. Species that reproduce sexually must maintain two different types of individuals, males and females, which can limit their ability to colonize new habitats as both sexes must be present. Therefore, there is an obvious benefit to organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of asexual reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead to solitary lifestyle have retain ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, males are not producing offspring themselves. In theory, asexual population could grow twice as fast. Nevertheless, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexuality so common? This is one of the important unanswered questions in biology and has been the focus of much research beginning in the latter half of the twentieth century. There are several possible explanations, one of which is that variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, sexually - reproducing population will leave more descendants than otherwise similar asexually - reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but, in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and genes are mixed into different combinations by process of meiosis. Meiosis is division of contents of nucleus, dividing chromosomes among gametes. The process of meiosis produces unique reproductive cells called gametes, which have half the number of chromosomes as parent cell. Fertilization, fusion of haploid gametes from two individuals, restores diploid condition. Thus, sexually - reproducing organisms alternate between haploid and diploid stages. However, ways in which reproductive cells are produced and timing between meiosis and fertilization vary greatly. There are three main categories of sexual life cycles: diploid - dominant, demonstrated by most animals; haploid - dominant, demonstrated by all fungi and some algae; and alternation of generations, demonstrated by plants and some algae.


Life Cycles of Sexually Reproducing Organisms

Fertilization and meiosis alternate in sexual life cycles. What happens between these two events depends on organisms ' reproductive strategy. The process of meiosis reduces chromosome numbers by half. Fertilization, joining of two haploid gametes, restores diploid condition. Some organisms have a multicellular diploid stage that is most obvious and only produces haploid reproductive cells. Animals, including humans, have this type of life cycle. Other organisms, such as fungi, have multicellular haploid stage that is most obvious. Plants and some algae have alternation of generations, in which they have multicellular diploid and haploid life stages that are apparent to different degrees depending on group. Nearly all animals employ a diploid - dominant life - cycle strategy in which only haploid cells produced by organism are gametes. Early in the development of embryo, specialized diploid cells, called germ cells, are produced within gonads. Germ cells are capable of mitosis to perpetuate germ cell line and meiosis to produce haploid gametes. Once haploid gametes are form, they lose the ability to divide again. There is no multicellular haploid life stage. Fertilization occurs with the fusion of two gametes, usually from different individuals, restoring the diploid state. Most fungi and algae employ life - cycle type in which the body of organismthe ecologically important part of the life cycleis haploid. Haploid cells that make up tissues of the dominant multicellular stage are formed by mitosis. During sexual reproduction, specialized haploid cells from two individualsdesignated and mating typesjoin to form diploid zygote. Zygote immediately undergoes meiosis to form four haploid cells called spores. Although these spores are haploid like parents, they contain new genetic combination from two parents. Spores can remain dormant for various time periods. Eventually, when conditions are favorable, spores form multicellular haploid structures through many rounds of mitosis. The third life - cycle type, employed by some algae and all plants, is a blend of haploid - dominant and diploid - dominant extremes. Species with alternation of generations have both haploid and diploid multicellular organisms as part of their life cycle. Haploid multicellular plants are called gametophytes, because they produce gametes from specialized cells. Meiosis is not directly involved in the production of gametes in this case, because the organism that produces gametes is already haploid. Fertilization between gametes forms diploid zygote. Zygote will undergo many rounds of mitosis and give rise to a diploid multicellular plant called sporophyte. Specialized cells of sporophyte will undergo meiosis and produce haploid spores. Spores will subsequently develop into gametophytes. Although all plants utilize some version of alternation of generations, relative size of sporophyte and gametophyte and relationship between them vary greatly. In plants such as moss, gametophyte organism is a free - living plant and sporophyte is physically dependent on gametophyte. In other plants, such as ferns, both gametophyte and sporophyte plants are free - living; however, sporophyte is much larger.

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External or Internal Fertilization

Animal reproduction is essential to the survival of species; it can occur through either asexual or sexual means. Reproduction is a biological process by which new offspring are produced from their parents. It is a fundamental feature of all known life that each individual organism exists as a result of reproduction. Most importantly, reproduction is necessary for the survival of species. Know methods of reproduction are broadly grouped into two main types: sexual and asexual. In asexual reproduction, individual can reproduce without involvement with another individual of that species. The division of bacterial cells into two daughter cells is an example of asexual reproduction. This type of reproduction produces genetically - identical organisms, whereas in sexual reproduction, genetic material of two individuals combines to produce offspring that are genetically different from their parents. During sexual reproduction, male gamete may be placed inside the female body for internal fertilization, or sperm and eggs may be released into the environment for external fertilization. Humans provide example of the former, while seahorses provide examples of the latter. Following the mating dance, female seahorses lay eggs on male seahorses ' abdominal brood pouch where they are fertilize. Eggs hatch and offspring develop in pouch for several weeks.


Asexual Reproduction

Asexual reproduction is a strategy used by a number of organisms. In fact, examples from each of six kingdoms of life have the ability to reproduce asexually. This process allows a single organism to pass on its genetic information from one generation to the next. Since this reproductive strategy only involves a single parent, genetic material passed on is identical to the parent organism - barring any mutations. This process therefore results in genetic continuity for that species. This cloning produces generations of organisms with identical or very similar traits: continuity results in very little variation throughout generations. Cells involved in the asexual process are produced via mitosis, which is used to replicate somatic or body cells of organism. You may remember mitosis from your Grade 10 Science course, but take a look at this video of eukaryotic cell undergoing process if you need refresher. Pay particular attention to names of phases and main events that occur in each of them. Asexual reproduction will often produce large numbers of offspring in a short amount of time. Bacteria is a prime example of this. The bacterium species Escherichia coli, commonly known as E. Coli, can replicate itself in as little as 20 minutes under ideal conditions. One bacterium becomes two, two becomes four, etc. This exponential growth can result in a mind - boggling number of organisms in hours. In fact, one single E. Coli cell can replicate into a population of two million cells in about seven hours! This short video clip illustrates the impact of an organism's exponential growth: This exponential growth comes with its own issues - as you will see when you investigate sustainability in the next Unit.


Sexual Reproduction

Most higher animals reproduce sexually by fusion of male and female gametes in the process of fertilization. The process of sexual reproduction in animals occurs via a complex cycle consisting of mitotic and meiotic cell divisions. In animals, reproductive organs and reproductive cells are well define. These cells then undergo meiotic divisions to form haploid gametes. Male gametes are term sperm whereas female gametes are term as eggs. The process of fertilization can be either internal or external. Either way, male gamete fuses with female gamete to form diploid zygote. Zygote then develops to form a new organism in due time. Reproduction might also be seasonal in some animals, like frogs that only reproduce during the rainy season. Most animals are unicellular and thus produce one of two gametes, but some might be hermaphrodites that produce both male and female gametes.


Sex Determination

Mammalian sex is determined genetically by the combination of X and Y chromosomes. Individuals homozygous for X are female and heterozygous individuals are male. In mammals, presence of the Y chromosome causes development of male characteristics and its absence results in female characteristics. 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 results in males and heterozygous results in female. Notice that this system is the opposite of the mammalian system because in birds, females has sex with different sex chromosomes. W appears to be essential in determining the sex of an individual, similar to the Y chromosome in mammals. Some fish, crustaceans, insects, and reptiles use the ZW system. More complicated chromosomal sex determining systems also exist. For example, some swordtail fish have three sex chromosomes in the 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 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, 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 other. If the individual is female first, it is term protogyny or first female, if it is male first, it is term protandry or first male. Oysters are born male, grow in size, and become female and lay eggs. Wrasses, family of reef fishes, are all sequential hermaphrodites. Some of these species live in closely coordinated schools with a dominant male and large numbers of smaller females. If male dies, female increases in size, changes sex, and becomes the new dominant male.

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The Red Queen Hypothesis

Outcrossing is the most prevalent mode of reproduction among plants and animals. Maintenance of outcrossing on such a large scale strongly suggests that there is a selective advantage for outcrossing relative to self - fertilization or asexual reproduction. Nonetheless, prevalence of outcrossing is puzzling, because it often incurs costs that are not associated with uniparental modes of reproduction. For example, many outcrossing species produce males that facilitate outcrossing, but are incapable of bearing offspring themselves, resulting in cost of males. Every male takes place of offspring - bearing progeny that could have been produce. Systematic loss of offspring - bearing progeny can reduce the numerical contribution of lineage by as much as fifty percent. Therefore, selective benefits of outcrossing must more than compensate for this fitness deficit to achieve high frequency in Nature. One selective benefit of outcrossing, relative to self - fertilization, is the capability to produce offspring with greater fitness under novel environmental conditions. Outcrossing can increase fitness and accelerate populations ' rate of adaptation to novel conditions by permitting genetic exchange between diverse lineages, promoting genetic variation among offspring, and allowing beneficial alleles to be quickly assembled into the same genome. In contrast, obligate selfing can impede adaptation by preventing genetic exchange, which results in loss of within - lineage genetic variation, and ultimately confines beneficial alleles to single lineage. Under novel environmental conditions, benefits of outcrossing can compensate for the cost of male production, but these benefits may be short live. Outcrossing is less likely to be favor after populations adapt to novel environment, as genetic exchange becomes less imperative, or perhaps even deleterious. Hence, long - term maintenance of outcrossing would seem to require that populations are constantly exposed to novel environmental conditions. The Red Queen Hypothesis provides a possible explanation for the long - term maintenance of outcrossing. Specifically, under the Red Queen Hypothesis, coevolutionary interactions between hosts and pathogens might generate ever - changing environmental conditions, and thus favor long - term maintenance of outcrossing relative to self - fertilization or asexual reproduction. The reason is that hosts are under selection to evade infection by pathogen,ss while pathogens are selected to infect hosts. Assuming that some form of genetic matching between host and pathogen determines the outcome of interactions, pathogen genotypes that infect most common host genotypes will be favor by natural selection. This may produce substantial and frequent changes in pathogen populations, thus rapidly changing the environment for the host population. Under these conditions, outcrossing can facilitate rapid adaptation by generating offspring with rare or novel genotypes, which are more likely to escape infection by coevolving pathogens. Conversely, selfing and asexual reproduction generate offspring with little or no genetic diversity, thus impeding the adaptive process and leaving them highly susceptible to infection by coevolving pathogens. The Red Queen Hypothesis has been empirically supported in studies of natural snail populations, which show that sexual reproduction is more common where parasites are common and adapted to infect the local host population.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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