83-516: (Redirected from Virgin Birth ) A virgin birth can refer to: Parthenogenesis , birth without fertilization Miraculous births , virgin birth in mythology and religion Virgin birth of Jesus Trinitarian doctrine of Jesus' nature Artificial insemination Russell case (1920s) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
166-460: A template strand by the DSB strand (see figure below). Nearby homologous regions of the template strand are often used for repair, which can give rise to either insertions or deletions in the genome if a non-homologous but complementary part of the template strand is used. Sequence similarity is a major player in crossover – crossover events are more likely to occur in long regions of close identity on
249-428: A 30% genome wide reduction in crossover numbers, and a large number of meioses with non exchange chromosomes. Nevertheless, this mutant gave rise to spore viability patterns suggesting that segregation of non-exchange chromosomes occurred efficiently. Thus in S. cerevisiae proper segregation apparently does not entirely depend on crossovers between homologous pairs. The grasshopper Melanoplus femur-rubrum
332-432: A chromosome with a ruptured end. She used modified patterns of gene expression on different sectors of leaves of her corn plants to show that transposable elements ("controlling elements") hide in the genome, and their mobility allows them to alter the action of genes at different loci. These elements can also restructure the genome, anywhere from a few nucleotides to whole segments of chromosome. Recombinases and primases lay
415-484: A common pattern. This finding suggested that chromosomal crossing over is a general characteristic of eukaryotic meiosis. There are two popular and overlapping theories that explain the origins of crossing-over, coming from the different theories on the origin of meiosis . The first theory rests upon the idea that meiosis evolved as another method of DNA repair , and thus crossing-over is a novel way to replace possibly damaged sections of DNA. The second theory comes from
498-427: A complete haploid complement of alleles on chromosomes that are independently selected from each pair of chromatids lined up on the metaphase plate. Without recombination, all alleles for those genes linked together on the same chromosome would be inherited together. Meiotic recombination allows a more independent segregation between the two alleles that occupy the positions of single genes, as recombination shuffles
581-425: A condensed space, it is thought that transposon regions undergoing a crossover event are more prone to erroneous complementary match-up; that is to say, a section of a chromosome containing a lot of identical sequences, should it undergo a crossover event, is less certain to match up with a perfectly homologous section of complementary code and more prone to binding with a section of code on a slightly different part of
664-445: A consequence, research on human parthenogenesis is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy. In 2022, researchers reported that they have achieved parthenogenesis in mice for viable offspring born from unfertilized eggs, addressing the problems of genomic imprinting by "targeted DNA methylation rewriting of seven imprinting control regions". In 1955, Helen Spurway ,
747-427: A drone father, while the production of further drones (males) depends on the queen (and occasionally workers) producing unfertilized eggs. This means that females (workers and queens) are always diploid, while males (drones) are always haploid, and produced parthenogenetically. Facultative parthenogenesis occurs when a female can produce offspring either sexually or via asexual reproduction. Facultative parthenogenesis
830-423: A fertile, viable female in a few, e.g., boas ). ZW offspring are produced by endoreplication before meiosis or by central fusion. ZZ and WW offspring occur either by terminal fusion or by endomitosis in the egg cell. In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female. In many hymenopteran insects such as honeybees, female eggs are produced sexually, using sperm from
913-419: A few vertebrates , such as some fish , amphibians , reptiles , and birds . This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice. Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers ), while others can switch between sexual reproduction and parthenogenesis. This
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#1732765958897996-590: A foundation of nucleotides along the DNA sequence. One such particular protein complex that is conserved between processes is RAD51 , a well conserved recombinase protein that has been shown to be crucial in DNA repair as well as cross over. Several other genes in D. melanogaster have been linked as well to both processes, by showing that mutants at these specific loci cannot undergo DNA repair or crossing over. Such genes include mei-41, mei-9, hdm, spnA, and brca2. This large group of conserved genes between processes supports
1079-620: A full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring. Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been introduced . Relying solely on parthenogenetic reproduction has several advantages for an invasive species : it obviates
1162-466: A gene. This means that any section of the genome with long sections of repetitive DNA is prone to crossover events. The presence of transposable elements is another influential element of non-homologous crossover. Repetitive regions of code characterize transposable elements; complementary but non-homologous regions are ubiquitous within transposons. Because chromosomal regions composed of transposons have large quantities of identical, repetitious code in
1245-412: A general source of mutation within the genome . The specific causes of non-homologous crossover events are unknown, but several influential factors are known to increase the likelihood of an unequal crossover. One common vector leading to unbalanced recombination is the repair of double-strand breaks (DSBs). DSBs are often repaired using homology directed repair, a process which involves invasion of
1328-494: A geneticist specializing in the reproductive biology of the guppy ( Lebistes reticulatus ), claimed that parthenogenesis may occur (though very rarely) in humans, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike. Sometimes an embryo may begin to divide without fertilization, but it cannot fully develop on its own; so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes
1411-617: A male and a female produces only females. The reason for this is the non-random segregation of the sex chromosomes 'X' and 'O' during spermatogenesis . Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals. For example, many cases of spontaneous parthenogenesis in sharks , some snakes , Komodo dragons , and a variety of domesticated birds were widely attributed to facultative parthenogenesis. These cases are examples of spontaneous parthenogenesis. The occurrence of such asexually produced eggs in sexual animals can be explained by
1494-414: A male is absent from the habitat or if it is unable to produce viable offspring. However, California condors and the tropical lizard Lepidophyma smithii both can produce parthenogenic offspring in the presence of males, indicating that facultative parthenogenesis may be more common than previously thought and is not simply a response to a lack of males. In aphids , a generation sexually conceived by
1577-505: A male is present and available for a female to breed with. In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non- sister chromosomes , a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions. Many taxa with heterogony have within them species that have lost
1660-424: A meiotic error, leading to eggs produced via automixis . Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means. Many species have transitioned to obligate parthenogenesis over evolutionary time. Well documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms. These transitions often occur as
1743-671: A million years. The success of those salamanders may be due to rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million. In addition, the Amazon molly is known to reproduce by gynogenesis. Hybridogenesis is a mode of reproduction of hybrids . Hybridogenetic hybrids (for example AB genome ), usually females, during gametogenesis exclude one of parental genomes (A) and produce gametes with unrecombined genome of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A)
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#17327659588971826-662: A non-specific protein synthesis inhibitor, enhances parthenote development in swine presumably by continual inhibition of MPF/cyclin B. As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote Parthenotes can be surgically transferred to a recipient oviduct for further development, but will succumb to developmental failure after ≈30 days of gestation. The swine parthenote placentae often appears hypo-vascular: see free image (Figure 1) in linked reference. Induced parthenogenesis in mice and monkeys often results in abnormal development. This
1909-439: A result of inbreeding or mutation within large populations. Some documented species, specifically salamanders and geckos, that rely on obligate parthenogenesis as their major method of reproduction. As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species), amphibians and fishes in nature for which males are no longer a part of the reproductive process. A female produces an ovum with
1992-665: A scaffold protein called SLX4 may participate in this regulation. Specifically, SLX4 knockout mice largely phenocopies the MUS81 knockout—once again, an elevated class I crossovers while normal chiasmata count. In FANCM knockout mice, the class II pathway is hyperactivated, resulting in increased numbers of crossovers that are independent of the MLH1/MLH3 pathway. In most eukaryotes , a cell carries two versions of each gene , each referred to as an allele . Each parent passes on one allele to each offspring. An individual gamete inherits
2075-409: A situation in which some combinations of genes or genetic markers occur more or less frequently in a population than would be expected from their distances apart. This concept is applied when searching for a gene that may cause a particular disease . This is done by comparing the occurrence of a specific DNA sequence with the appearance of a disease. When a high correlation between the two is found, it
2158-550: A species. During DNA replication , each strand of DNA is used as a template for the creation of new strands using a partially-conserved mechanism; proper functioning of this process results in two identical, paired chromosomes, often called sisters. Sister chromatid crossover events are known to occur at a rate of several crossover events per cell per division in eukaryotes. Most of these events involve an exchange of equal amounts of genetic information, but unequal exchanges may occur due to sequence mismatch. These are referred to by
2241-401: A sperm cell; this must have happened early in development, as self-activated eggs quickly lose their ability to be fertilized. The unfertilized cells eventually duplicated their DNA, boosting their chromosomes to 46. When the unfertilized cells hit a developmental block, the fertilized cells took over and developed that tissue. The boy had asymmetrical facial features and learning difficulties but
2324-606: A type of benign tumor called an ovarian teratoma . Spontaneous ovarian activation is not rare and has been known about since the 19th century. Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs and other structures, but are non-viable. In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as white blood cells ) to be lacking in any genetic content from his father. Scientists believe that an unfertilized egg began to self-divide but then had some (but not all) of its cells fertilized by
2407-401: A variety of names, including non-homologous crossover, unequal crossover, and unbalanced recombination, and result in an insertion or deletion of genetic information into the chromosome. While rare compared to homologous crossover events, these mutations are drastic, affecting many loci at the same time. They are considered the main driver behind the generation of gene duplications and are
2490-460: Is because in asexual reproduction a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who will not give birth. Some species can produce both sexually and through parthenogenesis, and offspring in the same clutch of a species of tropical lizard can be a mix of sexually produced offspring and parthenogenically produced offspring. In California condors, facultative parthenogenesis can occur even when
2573-480: Is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring for development to proceed normally. A mammal created by parthenogenesis would have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities. It has been suggested that defects in placental folding or interdigitation are one cause of swine parthenote abortive development. As
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2656-421: Is because recombination is greatly influenced by the proximity of one gene to another. If two genes are located close together on a chromosome, the likelihood that a recombination event will separate these two genes is less than if they were farther apart. Genetic linkage describes the tendency of genes to be inherited together as a result of their location on the same chromosome. Linkage disequilibrium describes
2739-478: Is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy or heterogony ). The switch between sexuality and parthenogenesis in such species may be triggered by the season ( aphid , some gall wasps ), or by a lack of males or by conditions that favour rapid population growth ( rotifers and cladocerans like Daphnia ). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This
2822-444: Is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies ; presumably, this is the default reproductive mode of all species in this insect order. Facultative parthenogenesis has generally been believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if
2905-628: Is known as a chiasma . The Holliday junction is a tetrahedral structure which can be 'pulled' by other recombinases, moving it along the four-stranded structure. The MSH4 and MSH5 proteins form a hetero-oligomeric structure ( heterodimer ) in yeast and humans. In the yeast Saccharomyces cerevisiae MSH4 and MSH5 act specifically to facilitate crossovers between homologous chromosomes during meiosis . The MSH4/MSH5 complex binds and stabilizes double Holliday junctions and promotes their resolution into crossover products. An MSH4 hypomorphic (partially functional) mutant of S. cerevisiae showed
2988-406: Is likely that the appropriate gene sequence is really closer Crossovers typically occur between homologous regions of matching chromosomes , but similarities in sequence and other factors can result in mismatched alignments. Most DNA is composed of base pair sequences repeated very large numbers of times. These repetitious segments, often referred to as satellites, are fairly homogeneous among
3071-419: Is linked to DNA repair or bacterial transformation, as the two do not appear to be mutually exclusive. It is likely that crossing over may have evolved from bacterial transformation, which in turn developed from DNA repair, thus explaining the links between all three processes. Meiotic recombination may be initiated by double-stranded breaks that are introduced into the DNA by exposure to DNA damaging agents, or
3154-423: Is linked, if not identical, to chromosomal crossover. Morgan immediately saw the great importance of Janssens' cytological interpretation of chiasmata to the experimental results of his research on the heredity of Drosophila . The physical basis of crossing over was first demonstrated by Harriet Creighton and Barbara McClintock in 1931. The linked frequency of crossing over between two gene loci ( markers )
3237-531: Is more complicated. In some cases, the offspring are haploid (e.g., male ants ). In other cases, collectively called automictic parthenogenesis , the ploidy is restored to diploidy by various means. This is because haploid individuals are not viable in most species. In automictic parthenogenesis, the offspring differ from one another and from their mother. They are called half clones of their mother. Automixis includes several reproductive mechanisms, some of which are parthenogenetic. Diploidy can be restored by
3320-495: Is present is due to crossing over. In the case of endomitosis after meiosis, the offspring is completely homozygous and has only half the mother's genetic material. This can result in parthenogenetic offspring being unique from each other and from their mother. In apomictic parthenogenesis, the offspring are clones of the mother and hence (except for aphids) are usually female. In the case of aphids, parthenogenetically produced males and females are clones of their mother except that
3403-438: Is restored by fertilization of these gametes with gametes from the first species (AA, sexual host, usually male). Hybridogenesis is not completely asexual, but hemiclonal: half the genome is passed to the next generation clonally , unrecombined, intact (B), other half sexually , recombined (A). This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from
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3486-435: Is the crossing-over value . For fixed set of genetic and environmental conditions, recombination in a particular region of a linkage structure ( chromosome ) tends to be constant and the same is then true for the crossing-over value which is used in the production of genetic maps . When Hotta et al. in 1977 compared meiotic crossing-over ( recombination ) in lily and mouse they concluded that diverse eukaryotes share
3569-421: Is the exchange of genetic material during sexual reproduction between two homologous chromosomes ' non-sister chromatids that results in recombinant chromosomes . It is one of the final phases of genetic recombination , which occurs in the pachytene stage of prophase I of meiosis during a process called synapsis . Synapsis begins before the synaptonemal complex develops and is not completed until near
3652-471: Is the restoration of the parental genotype. One class of MMR in particular, MutSβ, is known to initiate the correction of insertion-deletion mismatches of up to 16 nucleotides. Little is known about the excision process in eukaryotes, but E. coli excisions involve the cleaving of a nick on either the 5' or 3' strand, after which DNA helicase and DNA polymerase III bind and generate single-stranded proteins, which are digested by exonucleases and attached to
3735-473: The HLA region of DNA. These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and would allow derivatives of these cells to be implanted without immune rejection. With selection of oocyte donors according to HLA haplotype , it would be possible to generate a bank of cell lines whose tissue derivatives, collectively, could be MHC-matched with a significant number of individuals within
3818-467: The Spo11 protein. One or more exonucleases then digest the 5' ends generated by the double-stranded breaks to produce 3' single-stranded DNA tails (see diagram). The meiosis-specific recombinase Dmc1 and the general recombinase Rad51 coat the single-stranded DNA to form nucleoprotein filaments. The recombinases catalyze invasion of the opposite chromatid by the single-stranded DNA from one end of
3901-760: The X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system , they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female). Parthenogenesis is a form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization . It occurs naturally in some plants, algae , invertebrate animal species (including nematodes , some tardigrades , water fleas , some scorpions , aphids , some mites, some bees , some Phasmatodea , and parasitic wasps ), and
3984-415: The mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he contributed a major breakthrough to stem cell research by creating human embryos using parthenogenesis. A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with
4067-466: The statistical probability that another offspring will have the same combination. This principle of " independent assortment " of genes is fundamental to genetic inheritance. However, the frequency of recombination is actually not the same for all gene combinations. This leads to the notion of " genetic distance ", which is a measure of recombination frequency averaged over a (suitably large) sample of pedigrees. Loosely speaking, one may say that this
4150-488: The Greek παρθένος , parthénos , 'virgin' + γένεσις , génesis , 'creation' ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization . In animals , parthenogenesis means development of an embryo from an unfertilized egg cell . In plants , parthenogenesis is a component process of apomixis . In algae , parthenogenesis can mean
4233-519: The International Stem Cell Corporation of California announced that Elena Revazova had intentionally created human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way for creating stem cells genetically matched to a particular female to treat degenerative diseases. The same year, Revazova and ISCC published an article describing how to produce human stem cells that are homozygous in
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#17327659588974316-599: The Southern Hemisphere. Parthenogenesis does not apply to isogamous species. Parthenogenesis occurs naturally in aphids , Daphnia , rotifers , nematodes , and some other invertebrates, as well as in many plants. Among vertebrates , strict parthenogenesis is only known to occur in lizards, snakes, birds, and sharks. Fish, amphibians, and reptiles make use of various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis). The first all-female (unisexual) reproduction in vertebrates
4399-427: The allele content between homologous chromosomes. Recombination results in a new arrangement of maternal and paternal alleles on the same chromosome. Although the same genes appear in the same order, some alleles are different. In this way, it is theoretically possible to have any combination of parental alleles in an offspring, and the fact that two alleles appear together in one offspring does not have any influence on
4482-406: The break. Next, the 3' end of the invading DNA primes DNA synthesis, causing displacement of the complementary strand, which subsequently anneals to the single-stranded DNA generated from the other end of the initial double-stranded break. The structure that results is a cross-strand exchange , also known as a Holliday junction . The contact between two chromatids that will soon undergo crossing-over
4565-424: The case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids. If terminal fusion (restitutional meiosis of anaphase II or the fusion of its products) occurs, a little over half the mother's genetic material is present in the offspring and the offspring are mostly homozygous. This is because at anaphase II the sister chromatids are separated and whatever heterozygosity
4648-540: The chromosome. This results in unbalanced recombination, as genetic information may be either inserted or deleted into the new chromosome, depending on where the recombination occurred. While the motivating factors behind unequal recombination remain obscure, elements of the physical mechanism have been elucidated. Mismatch repair (MMR) proteins, for instance, are a well-known regulatory family of proteins, responsible for regulating mismatched sequences of DNA during replication and escape regulation. The operative goal of MMRs
4731-481: The class I crossovers. The remaining are the result of the class II pathway, which is regulated by MUS81 endonuclease and FANCM translocase. There are interconnections between these two pathways—class I crossovers can compensate for the loss of class II pathway. In MUS81 knockout mice, class I crossovers are elevated, while total crossover counts at chiasmata are normal. However, the mechanisms underlining this crosstalk are not well understood. A recent study suggests that
4814-581: The development of an embryo from either an individual sperm or an individual egg. Parthenogenesis occurs naturally in some plants, algae , invertebrate animal species (including nematodes , some tardigrades , water fleas , some scorpions , aphids , some mites, some bees , some Phasmatodea , and parasitic wasps ), and a few vertebrates , such as some fish , amphibians , and reptiles . This type of reproduction has been induced artificially in animal species that naturally reproduce through sex, including fish, amphibians, and mice. Normal egg cells form in
4897-409: The doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed. This is an endomitotic cycle. Diploidy can also be restored by fusion of the first two blastomeres , or by fusion of the meiotic products. The chromosomes may not separate at one of the two anaphases (restitutional meiosis)l; or the nuclei produced may fuse; or one of the polar bodies may fuse with
4980-490: The egg cell at some stage during its maturation. Some authors consider all forms of automixis sexual as they involve recombination. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined. The criterion for sexuality varies from all cases of restitutional meiosis, to those where
5063-422: The end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome. Crossing over was described, in theory, by Thomas Hunt Morgan ; the term crossover was coined by Morgan and Eleth Cattell. Hunt relied on the discovery of Frans Alfons Janssens who described the phenomenon in 1909 and had called it "chiasmatypie". The term chiasma
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#17327659588975146-487: The father's side. This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"): Other examples where hybridogenesis is at least one of modes of reproduction include i.e. Parthenogenesis, in the form of reproduction from a single individual (typically a god), is common in mythology, religion, and folklore around
5229-630: The first ever cytological demonstration of crossing over in meiosis. Working with student Harriet Creighton, McClintock also made significant contributions to the early understanding of codependency of linked genes. Crossing over and DNA repair are very similar processes, which utilize many of the same protein complexes. In her report, "The Significance of Responses of the Genome to Challenge", McClintock studied corn to show how corn's genome would change itself to overcome threats to its survival. She used 450 self-pollinated plants that received from each parent
5312-405: The formation of overhangs on the sides of the broken DNA strand, allowing for the annealing of a new strand. Bacterial transformation itself has been linked to DNA repair many times. The second theory comes from the idea that meiosis evolved from bacterial transformation , with the function of propagating genetic diversity. Thus, this evidence suggests that it is a question of whether cross over
5395-401: The fusion of its products), the offspring get all to more than half of the mother's genetic material and heterozygosity is mostly preserved (if the mother has two alleles for a locus, it is likely that the offspring will get both). This is because in anaphase I the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion. In
5478-491: The human population. After an independent investigation, it was revealed that the discredited South Korean scientist Hwang Woo-Suk unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result later found to be fabricated. Further examination of the chromosomes of these cells show indicators of parthenogenesis in those extracted stem cells, similar to those found in
5561-399: The idea that meiosis evolved from bacterial transformation , with the function of propagating diversity. In 1931, Barbara McClintock discovered a triploid maize plant. She made key findings regarding corn's karyotype, including the size and shape of the chromosomes. McClintock used the prophase and metaphase stages of mitosis to describe the morphology of corn's chromosomes, and later showed
5644-499: The males lack one of the X chromosomes (XO). When meiosis is involved, the sex of the offspring depends on the type of sex determination system and the type of apomixis. In species that use the XY sex-determination system , parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), ZZ (male), or WW (non-viable in most species, but
5727-573: The metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations, and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis. To initiate parthenogenesis of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide,
5810-403: The need for individuals in a very sparse initial population to search for mates; and an exclusively female sex distribution allows a population to multiply and invade more rapidly (potentially twice as fast). Examples include several aphid species and the willow sawfly, Nematus oligospilus , which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into
5893-427: The nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences. The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosis or when central fusion occurs (restitutional meiosis of anaphase I or
5976-404: The offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation. Parthenogenetic offspring in species that use either the XY or
6059-463: The phenomenon is called deuterotoky. Parthenogenesis can occur without meiosis through mitotic oogenesis. This is called apomictic parthenogenesis . Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids. Parthenogenesis involving meiosis
6142-444: The process of meiosis and are haploid , with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles . In some types of parthenogenesis
6225-428: The requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some salamanders of the genus Ambystoma are gynogenetic and appear to have been so for over
6308-454: The sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis. The production of female offspring by parthenogenesis is referred to as thelytoky (e.g., aphids) while the production of males by parthenogenesis is referred to as arrhenotoky (e.g., bees). When unfertilized eggs develop into both males and females,
6391-568: The theory of a close evolutionary relationship. Furthermore, DNA repair and crossover have been found to favor similar regions on chromosomes. In an experiment using radiation hybrid mapping on wheat's ( Triticum aestivum L. ) 3B chromosome, crossing over and DNA repair were found to occur predominantly in the same regions. Furthermore, crossing over has been correlated to occur in response to stressful, and likely DNA damaging, conditions. The process of bacterial transformation also shares many similarities with chromosomal cross over, particularly in
6474-560: The title Virgin birth . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Virgin_birth&oldid=1224915425 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Parthenogenesis Parthenogenesis ( / ˌ p ɑːr θ ɪ n oʊ ˈ dʒ ɛ n ɪ s ɪ s , - θ ɪ n ə -/ ; from
6557-415: The world, including in ancient Greek myth ; for example, Athena was born from the head of Zeus . In Christianity and Islam, there is the virgin birth of Jesus ; there are stories of miraculous births in other religions including Islam. The theme is one of several aspects of reproductive biology explored in science fiction . Chromosomal crossover Chromosomal crossover , or crossing over ,
6640-487: The zygotene-early pachytene stages caused a significant increase in mean cell chiasma frequency. Chiasma frequency was scored at the later diplotene-diakinesis stages of meiosis. These results suggest that X-rays induce DNA damages that are repaired by a crossover pathway leading to chiasma formation. Double strand breaks (DSBs) are repaired by two pathways to generate crossovers in eukaryotes. The majority of them are repaired by MutL homologs MLH1 and MLH3, which defines
6723-488: Was described in the fish Poecilia formosa in 1932. Since then at least 50 species of unisexual vertebrate have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders. Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring. During oocyte development, high metaphase promoting factor (MPF) activity causes mammalian oocytes to arrest at
6806-414: Was exposed to an acute dose of X-rays during each individual stage of meiosis , and chiasma frequency was measured. Irradiation during the leptotene - zygotene stages of meiosis (that is, prior to the pachytene period in which crossover recombination occurs) was found to increase subsequent chiasma frequency. Similarly, in the grasshopper Chorthippus brunneus , exposure to X-irradiation during
6889-440: Was otherwise healthy. This would make him a parthenogenetic chimera (a child with two cell lineages in his body). While over a dozen similar cases have been reported since then (usually discovered after the patient demonstrated clinical abnormalities), there have been no scientifically confirmed reports of a non-chimeric, clinically healthy human parthenote (i.e. produced from a single, parthenogenetic-activated oocyte). In 2007,
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