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Oogonial Stem Cells
Oogonial stem cells (OSCs), also known as egg precursor cells or female germline cells, are diploid germline cells with stem cell characteristics: the ability to renew and differentiate into other cell types, different from their tissue of origin. Present in invertebrates and some lower vertebrate species, they have been extensively studied in ''Caenorhabditis elegans'', ''Drosophila melanogaster''. OSCs allow the production of new female reproductive cells (oocytes) by the process of oogenesis during an organism's reproductive life. Invertebrates ''Caenorhabditis elegans'' The nematode ''Caenorhabditis elegans'' (''C. elegans'') are nematodes can have hermaphroditic or male reproductive capabilities. In males, only spermatogenesis occurs; hermaphrodites can produce spermatozoa until adulthood, when oogenesis takes over. All oogonial stem cells in ''C. elegans'' are derived from one distal-tip cell (DTC), which acts as a niche to ensure that germline proliferation continues. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair, which chromosomes naturally exist as. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): monoploid (1 set), diploid (2 sets), triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid or septaploid (7 sets), etc. The generic term polyploid is often used to describe cells with three or more chromosome sets. Virtually all sexually reproducing organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary widely between different organisms, between different tissues within the same organism, and at different stages in an organism's life cycle. Half ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Germline
In biology and genetics, the germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny (offspring). In other words, they are the cells that form the egg, sperm and the fertilised egg. They are usually differentiated to perform this function and segregated in a specific place away from other bodily cells. As a rule, this passing-on happens via a process of sexual reproduction; typically it is a process that includes systematic changes to the genetic material, changes that arise during recombination, meiosis and fertilization for example. However, there are many exceptions across multicellular organisms, including processes and concepts such as various forms of apomixis, autogamy, automixis, cloning or parthenogenesis. The cells of the germline are called germ cells. For example, gametes such as a sperm and an egg are germ cells. So are the cells that divide to produce gametes, called gametocytes, the cells that produce thos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loris
Loris is the common name for the strepsirrhine mammals of the subfamily Lorinae (sometimes spelled Lorisinae) in the family Lorisidae. ''Loris'' is one genus in this subfamily and includes the slender lorises, ''Nycticebus'' is the genus containing the slow lorises, and ''Xanthonycticebus'' is the genus name of the pygmy slow loris. Description Lorises are nocturnal and arboreal. They are found in tropical and woodland forests of India, Sri Lanka, and parts of southeast Asia. Loris locomotion is a slow and cautious climbing form of quadrupedalism. Some lorises are almost entirely insectivorous, while others also include fruits, gums, leaves, and slugs in their diet. Female lorises practice infant parking, leaving their infants behind in trees or bushes. Before they do this, they bathe their young with allergenic saliva that is acquired by licking patches on the insides of their elbows, which produce a mild toxin that discourages most predators, though orangutans occasionally e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ovariole
An ovariole is a tubular component of the insect ovary, and the basic unit of egg production. Each ovariole is composed of a germarium (the germline stem cell niche) at the anterior tip, a set of developing oocytes contained within follicles, and a posterior connection to a common oviduct. While most insects have two ovaries, the number of ovarioles within each ovary varies across insect species. This number may also be variable across individuals within a species, or between the left and right ovaries within an individual. Types Ovarioles are often classified into one of several types by the presence and position of nurse cells. These specialized cells provide nutrition and molecules important for embryonic patterning to the developing oocyte. Ovarioles that lack nurse cells are referred to as ''panoistic'' and ovarioles with nurse cells are referred to as ''meroistic''. Meroistic ovarioles are further classified according to where nurse cells are located. In ''polytrophic m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. The ovaries also secrete hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause. It is also an endocrine gland because of the various hormones that it secretes. Structure The ovaries are considered the female gonads. Each ovary is whitish in color and located alongside the lateral wall of the uterus in a region called the ovarian fossa. The ovarian fossa is the region that is bounded by the external iliac artery and in front of the ureter and the internal iliac artery. This area is about 4 cm x 3 cm x 2 cm in size.Daftary, Shirish; Chakravarti, Sudip (2011). Manual of Obstetrics, 3rd Edition. Elsevier. pp. 1-16. . The ovarie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dioecy
Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is biparental reproduction. Dioecy has costs, since only about half the population directly produces offspring. It is one method for excluding self-fertilization and promoting allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population. Plants have several other methods of preventing self-fertilization including, for example, dichogamy, herkogamy, and self-incompatibility. Dioecy is a dimorphic sexual system, alongside gynodioecy and androdioecy. In zoology In zoology, dioecious species may be opposed to hermaphroditic species, meaning that an individual is either male or female, in which case the synonym gonochory is more often used. Most animal species are dioecious (gon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prophase
Prophase () is the first stage of cell division in both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase. The main occurrences in prophase are the condensation of the chromatin reticulum and the disappearance of the nucleolus. Staining and microscopy Microscopy can be used to visualize condensed chromosomes as they move through meiosis and mitosis. Various DNA stains are used to treat cells such that condensing chromosomes can be visualized as the move through prophase. The giemsa G-banding technique is commonly used to identify mammalian chromosomes, but utilizing the technology on plant cells was originally difficult due to the high degree of chromosome compaction in plant cells. G-banding was fully realized for plant chromosomes in 1990. During both meiotic and mitotic prophase, giemsa staining can be applied to cells to elicit G-banding in chromosomes. Silver staining, a more modern technology, in conjunction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells 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 female will fuse to create a cell with two copies of each chromosome again, the zygote. 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 chr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anatomical Terms Of Location
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes. The meaning of terms that are used can change depending on whether an organism is bipedal or quadrupedal. Additionally, for some animals such as invertebrates, some terms may not have any meaning at all; for example, an animal that is radially symmetrical will have no anterior surface, but can still have a description that a part is close to the middle ("proximal") or further from the middle ("distal"). International organisations have determined vocabularies that are often used as standard vocabularies for subdisciplines of anatom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintained. Therefore, mitosis is also known as equational division. In general, mitosis is preceded by S phase of interphase (during which DNA replication occurs) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis altogether define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are preprophase (specific to plant cells), prophase ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stem-cell Niche
Stem-cell niche refers to a microenvironment, within the specific anatomic location where stem cells are found, which interacts with stem cells to regulate cell fate. The word 'niche' can be in reference to the ''in vivo'' or ''in vitro'' stem-cell microenvironment. During embryonic development, various niche factors act on embryonic stem cells to alter gene expression, and induce their proliferation or differentiation for the development of the fetus. Within the human body, stem-cell niches maintain adult stem cells in a quiescent state, but after tissue injury, the surrounding micro-environment actively signals to stem cells to promote either self-renewal or differentiation to form new tissues. Several factors are important to regulate stem-cell characteristics within the niche: cell–cell interactions between stem cells, as well as interactions between stem cells and neighbouring differentiated cells, interactions between stem cells and adhesion molecules, extracellular matrix co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
