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Cytogeneticist
Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping, analysis of G-banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent ''in situ'' hybridization (FISH) and comparative genomic hybridization (CGH). History Beginnings Chromosomes were first observed in plant cells by Carl Nägeli in 1842. Their behavior in animal (salamander) cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, von Waldeyer in 1888. The next stage took place after the development of genetics in the early 20th century, when it was appreciated that the set of chromosomes (the karyotype) was the carrier of the genes. Levitsky seems to have bee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Cytogenetics
Molecular cytogenetics combines two disciplines, molecular biology and cytogenetics, and involves the analysis of chromosome structure to help distinguish normal and cancer-causing cells. Human cytogenetics began in 1956 when it was discovered that normal human cells contain 46 chromosomes. However, the first microscopic observations of chromosomes were reported by Arnold, Flemming, and Hansemann in the late 1800s. Their work was ignored for decades until the actual chromosome number in humans was discovered as 46. In 1879, Arnold examined sarcoma and carcinoma cells having very large nuclei. Today, the study of molecular cytogenetics can be useful in diagnosing and treating various malignancies such as hematological malignancies, brain tumors, and other precursors of cancer. The field is overall focused on studying the evolution of chromosomes, more specifically the number, structure, function, and origin of chromosome abnormalities. It includes a series of techniques referred to a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and noncoding genes. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. These genes make up different DNA sequences called genotypes. Genotypes along with environmental and developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes (many different genes) as well as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypotonicity
In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane-impermeable solutes across a cell membrane which determine the direction and extent of osmotic flux. It is commonly used when describing the swelling-versus-shrinking response of cells immersed in an external solution. Unlike osmotic pressure, tonicity is influenced only by solutes that cannot cross the membrane, as only these exert an effective osmotic pressure. Solutes able to freely cross the membrane do not affect tonicity because they will always equilibrate with equal concentrations on both sides of the membrane without net solvent movement. It is also a factor affecting imbibition. There are three classifications of tonicity that one solution can have relative to another: ''hypertonic'', ''hypotonic'', and ''isotonic''.A hypoton ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The New York Times
''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid digital media, digital subscribers. It also is a producer of popular podcasts such as ''The Daily (podcast), The Daily''. Founded in 1851 by Henry Jarvis Raymond and George Jones (publisher), George Jones, it was initially published by Raymond, Jones & Company. The ''Times'' has won List of Pulitzer Prizes awarded to The New York Times, 132 Pulitzer Prizes, the most of any newspaper, and has long been regarded as a national "newspaper of record". For print it is ranked List of newspapers by circulation, 18th in the world by circulation and List of newspapers in the United States, 3rd in the U.S. The paper is owned by the New York Times Company, which is Public company, publicly traded. It has been governed by the Sulzberger family since 189 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Guardian
''The Guardian'' is a British daily newspaper. It was founded in 1821 as ''The Manchester Guardian'', and changed its name in 1959. Along with its sister papers ''The Observer'' and ''The Guardian Weekly'', ''The Guardian'' is part of the Guardian Media Group, owned by the Scott Trust Limited, Scott Trust. The trust was created in 1936 to "secure the financial and editorial independence of ''The Guardian'' in perpetuity and to safeguard the journalistic freedom and liberal values of ''The Guardian'' free from commercial or political interference". The trust was converted into a limited company in 2008, with a constitution written so as to maintain for ''The Guardian'' the same protections as were built into the structure of the Scott Trust by its creators. Profits are reinvested in journalism rather than distributed to owners or shareholders. It is considered a newspaper of record in the UK. The editor-in-chief Katharine Viner succeeded Alan Rusbridger in 2015. Since 2018, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Albert Levan
Albert Levan (8 March 1905 – 28 March 1998) was a Swedish botanist and geneticist. Albert Levan is best known today for co-authoring the report in 1956 that humans had forty-six chromosomes (instead of forty-eight, as previously believed). This epochal discovery was made by Joe Hin Tjio in Levan's laboratory. Originally specialising in plant cytology, Levan later turned to the similarities in the chromosome structure of cancer cells and errors introduced to plant cells via chemical or radioactive elements. These studies later led to examination of chromosomes in animal cells. Levan was elected a member of the Royal Swedish Academy of Sciences in 1967. He was cited by professor Bryan Sykes Bryan Clifford Sykes (9 September 1947 – 10 December 2020) was a British geneticist and science writer who was a Fellow of Wolfson College and Emeritus Professor of human genetics at the University of Oxford. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Joe Hin Tjio
Joe Hin Tjio (2 November 1919 – 27 November 2001), was an Indonesian-born American cytogeneticist. He was renowned as the first person to recognize the normal number of human chromosomes on December 22, 1955 at the Institute of Genetics of the University of Lund in Sweden, where Tjio was a visiting scientist. Early life Tjio (whose name is pronounced ''CHEE-oh'') was born to Indonesian parents of Chinese origin in Pekalongan, Java, then part of the Dutch East Indies and later known as Indonesia. His father was a photographer. Tjio was educated in Dutch colonial schools, trained in agronomy in college, and did research on potato breeding. He was imprisoned for 3 years and tortured by the Japanese in a concentration camp during World War II. Career After the war ended, Tjio went to the Netherlands, whose government provided him with a fellowship for study in Europe. He worked in plant breeding in Denmark, Spain and Sweden. From 1948 to 1959 he did plant chromosome research in Za ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XY Sex-determination System
The XY sex-determination system is a sex-determination system used to classify many mammals, including humans, some insects (''Drosophila''), some snakes, some fish ( guppies), and some plants ('' Ginkgo'' tree). In this system, the sex of an individual is determined by a pair of sex chromosomes. Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two different kinds of sex chromosomes (XY), and are called the heterogametic sex. In humans, the presence of the Y chromosome is responsible for triggering male development; in the absence of the Y chromosome, the fetus will undergo female development. There are various exceptions, such as individuals with Klinefelter syndrome (who have XXY chromosomes), Swyer syndrome (women with XY chromosomes), and XX male syndrome (men with XX chromosomes), however these exceptions are rare. In most species with XY sex determination, an organism must have at least one X chromosome in order ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theophilus Painter
Theophilus Shickel Painter (August 22, 1889 – October 5, 1969) was an American zoologist best known for his work on the structure and function of chromosomes, especially the sex-determination genes X and Y in humans. He was the first to discover that human sex was determined by an X/Y heteromorphic chromosomal pair mechanism.Rudle, Frank H. (2004)Theophilus Painter: First Steps Toward an Understanding of the Human Genome, ''J. Experimental Zoology, 301A'', 375–377. Retrieved 24 Jan. 2022. He also carried out work in identifying genes in fruit flies (''Drosophila''). His work exploited the giant polytene chromosomes in the salivary glands of ''Drosophila'' and other Dipteran larvae. Academic administration Painter joined the faculty at the University of Texas in 1916 and, except for military duty during World War I, stayed there his whole career. He was, in succession, associate professor, professor and distinguished professor of zoology. He served as acting president (1944– ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex-determination System
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. In some species there are hermaphrodites. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization. In some species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene (a "sex locus"), with a multitude of other genes following in a domino effect. In other cases, sex of a fetus is determined by environmental variables (such as temperature). The details of some sex-determination systems are not yet fully under ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XO Sex-determination System
The XO sex-determination system (sometimes X0 sex-determination system) is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two (XX). The letter O (sometimes a zero) signifies the lack of a second X. Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete. Its sperm normally contains either one X chromosome or no sex chromosomes at all. This system determines the sex of offspring among: * Most arachnidsBull, James J.; ''Evolution of sex determining mechanisms''; p. 17 with the exception of mites where a small majority are haplodiploid, * Almost all apterygote and Paleopteran insects (e.g., dragonflies, silverfish) * Most exopterygote insects (e.g., grasshoppers, crickets, cockroaches) * Some nematodes, cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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