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Pseudo-arrhenotoky
Pseudo-arrhenotoky or paternal genome elimination is the phenomenon where males develop from fertilized eggs but the paternal genome is heterochromatinized or lost in the somatic cells and not passed on to their offspring. This phenomenon occurs in certain mites, beetles and mealybugs and scale insects. When the males have a diploid number of chromosomes they are termed ''parahaploids'' as the paternal genes are not expressed at all. The paternal chromosomes are inactivated by heterochromatization in all the cells at an early embryonic stage. The adult cells have one set of inactive ''H chromosomes'' and one set of euchromatin ''E chromosomes''. These H chromosomes are eliminated from the sperm during or just before spermatogenesis. In a few other species all the cells in an adult are haploid due to elimination of the paternal chromosomes at an early developmental stage. This variant is called the ''diaspidid system'' after the scale insect clade (Diaspididae) where it was discover ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haplodiploid
Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky. Haplodiploidy determines the sex in all members of the insect orders Hymenoptera ( bees, ants, and wasps) and Thysanoptera ('thrips'). The system also occurs sporadically in some spider mites, Hemiptera, Coleoptera ( bark beetles), and rotifers. In this system, sex is determined by the number of sets of chromosomes an individual receives. An offspring formed from the union of a sperm and an egg develops as a female, and an unfertilized egg develops as a male. This means that the males have half the number of chromosomes that a female has, and are haploid. The haplodiploid sex-determination system has a number of peculiarities. For example, a male has no father and cannot have sons, but he has a grandfather and can have grandsons. Additionally, if a eusocial-insect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arrhenotoky
Arrhenotoky (from Greek -τόκος ''-tókos'' "birth of -" + ἄρρην ''árrhēn'' "male person"), also known as arrhenotokous parthenogenesis, is a form of parthenogenesis in which unfertilized eggs develop into males. In most cases, parthenogenesis produces exclusively female offspring, hence the distinction. The set of processes included under the term arrhenotoky depends on the author: arrhenotoky may be restricted to the production of males that are haploid (haplodiploidy); may include diploid males that permanently inactivate one set of chromosomes (parahaploidy); or may be used to cover all cases of males being produced by parthenogenesis (including such cases as aphids, where the males are XO diploids). The form of parthenogenesis in which females develop from unfertilized eggs is known as thelytoky; when both males and females develop from unfertilized eggs, the term "deuterotoky" is used. In the most commonly used sense of the term, arrhenotoky is synonymous with ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterochromatin
Heterochromatin is a tightly packed form of DNA or '' condensed DNA'', which comes in multiple varieties. These varieties lie on a continue between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a role in the expression of genes. Because it is tightly packed, it was thought to be inaccessible to polymerases and therefore not transcribed; however, according to Volpe et al. (2002), and many other papers since, much of this DNA is in fact transcribed, but it is continuously turned over via RNA-induced transcriptional silencing (RITS). Recent studies with electron microscopy and OsO4 staining reveal that the dense packing is not due to the chromatin. Constitutive heterochromatin can affect the genes near itself (e.g. position-effect variegation). It is usually repetitive and forms structural functions such as centromeres or telomeres, in addition to acting as an attractor for other gene-expression or repression signals. Facultative hete ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evidence of a close relationship. Most mites are tiny, less than in length, and have a simple, unsegmented body plan. The small size of most species makes them easily overlooked; some species live in water, many live in soil as decomposers, others live on plants, sometimes creating galls, while others again are Predation, predators or Parasitism, parasites. This last type includes the commercially destructive ''Varroa'' parasite of honey bees, as well as scabies mites of humans. Most species are harmless to humans, but a few are associated with allergies or may transmit diseases. The scientific discipline devoted to the study of mites is called acarology. Evolution and taxonomy The mites are not a defined taxon, but is used for two disti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beetle
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 described species, is the largest of all orders, constituting almost 40% of described insects and 25% of all known animal life-forms; new species are discovered frequently, with estimates suggesting that there are between 0.9 and 2.1 million total species. Found in almost every habitat except the sea and the polar regions, they interact with their ecosystems in several ways: beetles often feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. Some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae (ladybirds or ladybugs) eat aphids, scale insects, thrips, and other plant-sucking insects that damage crops. Beetles typically have a particularly hard e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mealybug
Mealybugs are insects in the family (biology), family Pseudococcidae, unarmored scale insects found in moist, warm habitats. Many species are considered pest (animal), pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a vector (epidemiology), vector for several plant diseases. Some ants live in symbiotic Ant#Relationships with other organisms, relationships with them, protecting them from predators and feeding off the Honeydew (secretion), honeydew which they excrete. Description Mealybugs are Sexual dimorphism, sexually dimorphic: females appear as nymphs, exhibiting reduced morphology, and lack wings, although unlike many female scale insects, they often retain legs and can move. Males are smaller, gnat-like and have wings. Since mealybugs (as well as all other Hemiptera) are hemimetabolous insects, they do not undergo complete metamorphosis in the true sense of the word. However, male mealybugs do exhibit a radical cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scale Insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the superfamily Coccoidea due to taxonomic uncertainties. Adult females typically have soft bodies and no limbs, and are concealed underneath domed scales, extruding quantities of wax for protection. Some species are hermaphroditic, with a combined ovotestis instead of separate ovaries and testes. Males, in the species where they occur, have legs and sometimes wings, and resemble small flies. Scale insects are herbivores, piercing plant tissues with their mouthparts and remaining in one place, feeding on sap. The excess fluid they imbibe is secreted as honeydew on which sooty mold tends to grow. The insects often have a mutualistic relationship with ants, which feed on the honeydew and protect them from predators. There are about 8,000 descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diaspididae
Diaspididae is the largest family of scale insects with over 2650 described species in around 400 genera. As with all scale insects, the female produces a waxy protective scale beneath which it feeds on its host plant. Diaspidid scales are far more substantial than those of most other families, incorporating the exuviae from the first two nymphal instars and sometimes faecal matter and fragments of the host plant. These can be complex and extremely waterproof structures rather resembling a suit of armor. For this reason these insects are commonly referred to as armored scale insects. As it is so robust and firmly attached to the host plant, the scale often persists long after the insect has died. Some African Diaspididae are attended by ants of genus ''Melissotarsus''. The ants appear to consume the armored scales because Diaspididae are completely naked when ant-attended; the ant nest itself remains completely hidden under the bark of the tree. Selected species Well-known spec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intragenomic Conflict
Intragenomic conflict refers to the evolutionary phenomenon where genes have phenotypic effects that promote their own transmission in detriment of the transmission of other genes that reside in the same genome. The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects cause their transmission to new organisms, and most genes achieve this by cooperating with other genes in the same genome to build an organism capable of reproducing and/or helping kin to reproduce. The assumption of the prevalence of intragenomic cooperation underlies the organism-centered concept of inclusive fitness. However, conflict among genes in the same genome may arise both in events related to reproduction (a selfish gene may "cheat" and increase its own presence in gametes or offspring above the expected according to fair Mendelian segregation and fair gametogenesis) and altruism (genes in the same genome may disagree on how to value ot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gynogenesis
Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed "sperm parasitism" in reference to the somewhat pointless role of male gametes. Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually. Gynogenesis is a disadvantageous mating system for males, as they are unable to pass on their DNA. The question as to why this reproductive mode exists, given that it appears to combine the disadvantages of both asexual and sexual reproduction, remains unsolved in the field of evolutionary biology. The male equivalent to this process is Androgenesis where th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thelytoky
Thelytoky (from the Greek ''thēlys'' "female" and ''tokos'' "birth") is a type of parthenogenesis in which females are produced from unfertilized eggs, as for example in aphids. Thelytokous parthenogenesis is rare among animals and reported in about 1,500 species, about 1 in 1000 of described animal species, according to a 1984 study. It is more common in invertebrates, like arthropods, but it can occur in vertebrates, including salamanders, fish, and reptiles such as some whiptail lizards. Thelytoky can occur by different mechanisms, each of which has a different impact on the level of homozygosity. It is found in several groups of Hymenoptera, including Apidae, Aphelinidae, Cynipidae, Formicidae, Ichneumonidae, and Tenthredinidae. It can be induced in Hymenoptera by the bacteria ''Wolbachia'' and ''Cardinium''. Arrhenotoky and thelytoky in Hymenoptera Hymenoptera (ants, bees, wasps, and sawflies) have a haplodiploid sex-determination system. They produce haploid males ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybridogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development of embryos occur in a gamete (egg or sperm) without combining with another gamete (e.g., egg and sperm fusing). 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 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, reptiles and birds). This type of reproduction has been induced artificially in a few sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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