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Aneugen
An aneugen is a substance that causes a daughter cell to have an abnormal number of chromosomes or aneuploidy. A substance's aneugenicity reflects its ability to induce aneuploidy. Unlike clastogens, aneugenic events do not damage the physical structure of the chromosome, but represent a deletion or insertion of an additional copy of a whole chromosome (i.e. with an intact Centromere). Aneugens and clastogens can be differentiated via certain stains, using the technique of Fluorescence in situ hybridization. Males, if exposed to certain environmental and/or occupational chemical hazards may face an increased risk of spermatozoa aneuploidy. Tobacco smoke contains chemicals that cause DNA damage (see Tobacco smoking#Health). Smoking also can induce aneuploidy. In this study of men with a moderate smoking habit showed an association with increased chromosome 13 disomy in spermatozoa by 3-fold and YY disomy by 2-fold. Occupational exposure to benzene is associated with a 2.8-fold ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clastogen
A clastogen is a mutagenic agent that disturbs normal DNA related processes or directly causes DNA strand breakages, thus causing the deletion, insertion, or rearrangement of entire chromosome sections. These processes are a form of mutagenesis which if left unrepaired, or improperly repaired, can lead to cancer. Known clastogens include acridine yellow, benzene, ethylene oxide, arsenic, phosphine, mimosine, actinomycin D, camptothecin, methotrexate, methyl acrylate, resorcinol and 5-fluorodeoxyuridine. Additionally, 1,2-dimethylhydrazine is a known colon carcinogen and shows signs of possessing clastogenic activity. There are many clastogens not listed here and research is ongoing to discover new clastogens. Some known clastogens only exhibit clastogenic activity in certain cell types, such as caffeine which exhibits clastogenic activity in plant cells. Researchers are interested in clastogens for researching cancer, as well as for other human health concerns such as the i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aneuploidy
Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), cell, for example a human somatic (biology), somatic cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more ploidy#Haploid and monoploid, complete sets of chromosomes. A cell with any number of complete chromosome sets is called a ''ploidy#Euploid, euploid'' cell. An extra or missing chromosome is a common cause of some genetic disorders. Some cancer cells also have abnormal numbers of chromosomes. About 68% of human solid tumors are aneuploid. Aneuploidy originates during cell division when the chromosomes do not separate properly between the two cells (nondisjunction). Most cases of aneuploidy in the autosomes result in miscarriage, and the most common extra autosomal chromosomes among live births are Down syndrome, 21, Edwards syndrome, 18 and Patau syndrome, 13. Chromosome abnormality, Chromosome abnormalities are detected in 1 of 160 live huma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Non-disjunction
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis/meiosis). There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy). Calvin Bridges and Thomas Hunt Morgan are credited with discovering nondisjunction in ''Drosophila melanogaster'' sex chromosomes in the spring of 1910, while working in the Zoological Laboratory of Columbia University. Proof of the chromosome theory of heredity emerged from these early studies of chromosome non-disjunction. Types In general, nondisjunction can occur in any form of cell division that involves ordered distribution of chromosomal material. Higher animals have three distinct forms of such cell divisions: Meiosis I an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centromere
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore. The physical role of the centromere is to act as the site of assembly of the kinetochores – a highly complex multiprotein structure that is responsible for the actual events of chromosome segregation – i.e. binding microtubules and signaling to the cell cycle machinery when all chromosomes have adopted correct attachments to the spindle, so that it is safe for cell division to proceed to completion and for cells to enter anaphase. There are, broadly speaking, two types of centromeres. "Point centromeres" bind to specific proteins that recognize particular DNA sequences with high efficiency. Any piece of DNA with the point centromere DNA sequence on it will typically form a centr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluorescence In Situ Hybridization
Fluorescence ''in situ'' hybridization (FISH) is a molecular cytogenetic technique that uses fluorescent probes that bind to only particular parts of a nucleic acid sequence with a high degree of sequence complementarity. It was developed by biomedical researchers in the early 1980s to detect and localize the presence or absence of specific DNA sequences on chromosomes. Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes. FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification. FISH can also be used to detect and localize specific RNA targets (mRNA, lncRNA and miRNA) in cells, circulating tumor cells, and tissue samples. In this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues. Probes – RNA and DNA In biology, a probe is a single strand of DNA or RNA that is complementary to a nucleotide sequence of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spermatozoon
A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is the male gamete that Fertilization, joins with an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, that normally develops into an embryo.) Sperm cells contribute approximately half of the nuclear gene, genetic information to the diploid offspring (excluding, in most cases, mitochondrial DNA). In mammals, the sex of the offspring is determined by the sperm cell: a spermatozoon bearing an X chromosome will lead to a female (XX) offspring, while one bearing a Y chromosome will lead to a male (XY) offspring. Sperm cells were first observed in Antonie van Leeuwenhoek's laboratory in 1677. Mammalian spermatozoa Humans The sperm cell of ''Homo sapiens'' is the small Gamete, reproductive cell produced by m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tobacco Smoking
Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or released from the mouth, as is generally done with pipes and cigars. The practice is believed to have begun as early as 5000–3000 BC in Mesoamerica and South America. Tobacco was introduced to Eurasia in the late 17th century by European colonists, where it followed common trade routes. The practice encountered criticism from its first import into the Western world onward but embedded itself in certain strata of several societies before becoming widespread upon the introduction of automated cigarette-rolling apparatus. Smoking is the most common method of consuming tobacco, and tobacco is the most common substance smoked. The agricultural product is often mixed with additives and then combusted. The resulting smoke, which contains various active substances, the most significant of which is the addictive psychostimulant drug nicotine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Y Chromosome
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the Y chromosome causes offspring produced in sexual reproduction to be of male sex. In mammals, the Y chromosome contains the SRY gene, which triggers development of male gonads. The Y chromosome is passed only from male parents to male offspring. Overview Discovery The Y chromosome was identified as a sex-determining chromosome by Nettie Stevens at Bryn Mawr College in 1905 during a study of the mealworm ''Tenebrio molitor''. Edmund Beecher Wilson independently discovered the same mechanisms the same year, working with Hemiptera. Stevens proposed that chromosomes always existed in pairs and that the smaller chromosome (now labelled "Y") was the pair of the X chromosome discovered in 1890 by Hermann Henking. She realized that th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X Chromosome
The X chromosome is one of the two sex chromosomes in many organisms, including mammals, and is found in both males and females. It is a part of the XY sex-determination system and XO sex-determination system. The X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart Y chromosome, for the next letter in the alphabet, following its subsequent discovery. Discovery It was first noted that the X chromosome was special in 1890 by Hermann Henking in Leipzig. Henking was studying the testicles of '' Pyrrhocoris'' and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining (''chroma'' in Greek means ''color''). Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of the object and consequently named it ''X element'', which later became X chromosome after it was established that it w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pesticide
Pesticides are substances that are used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all pesticide use globally. Most pesticides are used as plant protection products (also known as crop protection products), which in general protect plants from weeds, fungi, or insects. In general, a pesticide is a chemical or biological agent (such as a virus, bacterium, or fungus) that deters, incapacitates, kills, or otherwise discourages pests. Target pests can include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, cause nuisance, spread disease, or are disease vectors. Along with these benefits, pesticides also have drawbacks, such as potential toxicity to humans and other species. Definition The word pesticide derives from the Latin ''pestis'' (plagu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Insecticide
Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, industrial buildings, for vector control, and control of insect parasites of animals and humans. Acaricides, which kill mites and ticks, are not strictly insecticides, but are usually classified together with insecticides. Some insecticides (including common bug sprays) are effective against other non-insect arthropods as well, such as scorpions, spiders, etc. Insecticides are distinct from insect repellents, which repel but do not kill. Sales In 2016 insecticides were estimated to account for 18% of worldwide pesticide sales. Worldwide sales of insecticides in 2018 were estimated as $ 18.4 billion, of which 25% were neonicotinoids, 17% were pyrethroids, 13% were diamides, and the rest were many other classes which sold for less th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
