|
Parthenogenesis In Amphibians
Parthenogenesis is a form of reproduction where eggs develop without fertilization, resulting in unisexual species. This phenomenon is closely related with reproductive modes such as hybridogenesis, where fertilization occurs, but the paternal DNA is not passed on. Among amphibians, it is seen in numerous frog and salamander species, but has not been recorded in caecilians. Artificial parthenogenesis Haploid parthenogenesis has been achieved experimentally in amphibians, through approaches that could be considered artificial gynogenesis. Oscar Hertwig first achieved artificial parthenogenesis in frogs in 1911, using eggs fertilized by irradiated sperm. The radiation destroyed the DNA within the sperm, but nearly normal embryos were still produced. Gunther Hertwig repeated this experiment in 1924, using crosses between different frogs. A cross between a toad, ''Amietophrynus regularis'', and a frog, '' Rana fusca'', would not produce a viable embryo, but fertilization of a toad eg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Parthenogenesis
Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertilized Gametophyte, 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, 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 the process of meiosis and are haploid, with half as many chromosomes as t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Pelophylax Esculentus
The edible frog (''Pelophylax'' klepton, kl. ''esculentus'') is a Hybrid (biology), hybrid species of common European frog, also known as the common water frog or green frog (however, this latter term is also used for the North American species ''Rana clamitans''). It is used for food, particularly in France as well as Germany and Italy, for the delicacy frog legs. Females are between long, males between . This widespread and common frog has many common names, including European dark-spotted frog, European black-spotted pond frog, and European black-spotted frog. Distribution ''Pelophylax esculentus'' is endemic to Europe. It naturally occurs from the northern half of France to western Russia, and from Estonia and Denmark to Bulgaria and northern Italy. The edible frog is introduced in Spain, Norway and the United Kingdom. The natural range is nearly identical to that of ''Pool frog, P. lessonae''. Hybridogenesis ''Pelophylax'' kl. ''esculentus'' is the fertile Hybrid (bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Meiosis
Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one copy of each chromosome (haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and a female will fuse to create a zygote, a cell with two copies of each chromosome. Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Chromosomal Crossover
Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' sister chromatids, 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 is usually initiated before the synaptonemal complex develops and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome, resulting in Chiasma (genetics), chiasma which are the visible evidence of crossing over. History of discovery 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". Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Ambystoma Platineum
The silvery salamander (''Ambystoma platineum'') is a hybrid species of mole salamander from the United States of America and Canada. It is usually between long and slender, with many small silvery-blue spots on its back and sides. It is brownish grey, and the area around its vent is grey. A unisexual ''Ambystoma'' hybrid species, ''A. platineum'' has been grouped with other unisexual ambystomatids that take genetic material from Jefferson salamanders (''A. jeffersonianum''), streamside salamanders (''A. barbouri''), small-mouthed salamanders (''A. texanum''), tiger salamanders (''A. tigrinum'') and the blue-spotted salamander (''A. laterale''). Species name designations for unisexual ''Ambystoma'' are no longer in use. Instead, unisexual ''Ambystoma'' are now considered distinct biotypes rather than species. Behaviour Silvery Salamanders are gynogens; lacking its own males, they breed with males of a different species. The males' spermatophores only stimulate egg developme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Polyploidy
Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one from each of two parents; each set contains the same number of chromosomes, and the chromosomes are joined in pairs of homologous chromosomes. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes (eggs and sperm) by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis; the sporophyte generation is diploid and p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Ambystoma Barbouri
The streamside salamander (''Ambystoma barbouri'') is a species of mole salamander from North America, occurring in several Midwestern states of the US. Description The streamside salamander is a medium-sized amystomatid salamander. It typically has a relatively small head and a short rounded snout. The salamander's body is relatively short and flaccid. There are 14-15 distinct costal grooves when fully grown. The tail is fairly short and thick, and it contains costal grooves that correspond directly to the vertebrae. Coloring is typically a dark black background covered in lichen-like markings in gray and brown. The species has more teeth, with a unique cusp shape, in its maxillary and premaxillary positions than its close relatives teeth, and is somewhat stockier. Distribution and habitat The species is found in central Kentucky, southwestern Ohio, southeastern Indiana. There is an isolated population in Livingston County, Kentucky. Overall distribution is uncertain due to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Ambystoma Tigrinum
The tiger salamander (''Ambystoma tigrinum'') is a species of mole salamander and one of the largest terrestrial salamanders in North America. Description These salamanders usually grow to a length of with a lifespan of around 12–15 years. They are characterized by having markings varying in color on the back of their head, body, and tail. The coloring of these spots range from brownish yellow to greenish yellow, while the rest of their back is black or dark brown. They are smooth bodied, with costal grooves running down their sides to aid in moisture control. They have short snouts, thick necks, strong legs, and lengthy tails. Tiger salamanders also utilize specialized foot pads for burrowing.Tiger salamanders are a sexually dimorphic species, as the males are larger in body size, as well as have longer and higher tails than females. Some individuals, typically when their aquatic environment is well suited, will retain their larval characteristics and forego metamorphosis. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Ambystoma Jeffersonianum
The Jefferson salamander (''Ambystoma jeffersonianum'') is a mole salamander native to the northeastern United States, southern and central Ontario, and southwestern Quebec. It was named after Jefferson College in Pennsylvania. It is typically dark gray, brown, or black on its dorsal surface, but a lighter shade on its anterior. Some individuals may also have silver or blue specks on their sides; the area around the vent is usually gray. These salamanders are slender, with a wide nose and distinctive long toes, and range in size from . Like other mole salamanders, the Jefferson salamander burrows; they have well-developed lungs suited for this purpose. Nocturnal by nature, they can be spotted by day during the mating season. Breeding occurs in early spring, after the snow in the area has melted. Reproduction Eggs are laid in small agglomerations attached to submerged twigs or other natural support at the pond's edge. Clutches can contain between 5 and 60 eggs, averaging about 3 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
