Zygosity refers to the similarity of gene s for a trait inherited characteristic in an organism. If both genes are the same, the organism is Zygosity Homozygous homozygous for the trait. If both genes are different, the organism is Zygosity Heterozygous heterozygous for that trait. If one gene is missing, it is Zygosity Hemizygous hemizygous , and if both genes are missing, it is Zygosity Nullizygous nullizygous . Most eukaryote s have two matching sets of chromosomes , that is, they are diploid . Diploid organisms have the same genes on each of their two sets of chromosomes, except that the sequences of these genes may differ between the two chromosomes in a matching pair and that a few chromosomes may be mismatched as part of a Sex determination system Chromosomal determination sex determination system . The DNA sequence of a gene usually varies from one individual to another. Those variations are called alleles . Some genes have only one allele. Any variation from the DNA sequence of that allele will be fatal in the embryo, and the organism will never survive to be born. But most genes have two or more alleles. The frequency of different alleles varies throughout the population. Some genes may have two alleles with equal distribution. For other genes, one allele may be common, and another allele may be rare. Sometimes, one allele is a Genetic disorder disease causing variation while the other allele is healthy. Sometimes, the different variations in the alleles make no difference ... parent and one from the female parent. Zygosity is a description of whether those two alleles ... and allozygous Zygosity may also refer to the origin s of the alleles in a genotype. When the two ... monozygotic and dizygotic As discussed above, zygosity can be used in the context of a specific genetic locus example ref cite pmid 12654648 ref . In addition, the word zygosity may also be used ... sperm . In some cases the term zygosity is used in the context of a single chromosome. ref cite ... more details
Refimprove date December 2009 Overdominance is a condition in genetics where the phenotype of the Zygosity heterozygote lies outside of the phenotypical range of both Zygosity homozygote parents. The Gillespie Model Population Geneticist John H. Gillespie established the following model ref Gillespie 2004 ref class wikitable Genotype A sub 1 sub A sub 1 sub A sub 1 sub A sub 2 sub A sub 2 sub A sub 2 sub Relative fitness 1 1 hs 1 s Where h is the heterozygote effect and s is the recessive allele effect. Thus given a value for s ie 0 s 1 , h can yield the following information class wikitable h 0 A sub 1 sub dominant, A sub 2 sub recessive h 1 A sub 2 sub dominant, A sub 1 sub recessive 0 h 1 incomplete dominance h 0 overdominance h 1 Underdominance Overdominance in human genetics In humans, sickle cell anemia is a condition that is determined by a single polymorphism biology polymorphism . Possessors of this slightly deleterious allele have lower life expectancy, with Zygosity homozygotes rarely reaching 50 years of age. However, this allele also yields some resistance to malaria . Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While Zygosity homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia , Zygosity heterozygotes enjoy a partial resistance to both. In the Gillespie Model mentioned above, this situation corresponds to the case h 0. See also Polar overdominance Underdominance Notes Reflist 1 References cite book last Gillespie first John authorlink John H. Gillespie title Population Genetics A Concise Guide, Second Edition publisher Johns Hopkins University Press year 2004 isbn 0 8018 8008 4 Category Genetics Genetics stub es Sobredominancia ru zh ... more details
Image Carabelli.jpg thumb Diagram indicating cusp of Carabelli The cusp of Carabelli , or Carabelli s tubercle , or tuberculus anomalus of Georg Carabelli is a small additional cusp dentistry cusp at the Commonly used terms of relationship and comparison in dentistry mesiopalatal line angle of maxillary first molar s. This extra cusp is usually found on the first molar, and becomes progressively less likely in the second, third molars. This cusp is entirely absent in some individuals and present in others in a variety of forms. In some cases, Carabelli s cusp may rival the main cusps in size. Other related forms include ridges, pits, or furrows. This additional cusp was first described in 1842 by the Hungarian Georg Carabelli Carabelli Gy rgy , the court dentist of the Austrian Empire Austrian Emperor Franz. The cusp of Carabelli is a heritable feature. Kraus 1951 proposed that Zygosity homozygosity of a gene is responsible for a pronounced tubercle, whereas the Zygosity heterozygote shows slight grooves, pits, tubercles or bulge. Later studies showed that the development of this trait is affected by multiple genes. Carabelli s cusp is most common among Europeans 75 85 of individuals and rarest in Pacific Islands 35 45 . This cusp may also be found in dogs and cats. Further reading Simon Hillson. 1996. Dental Anthropology . Cambridge University Press. Tooth anatomy Category Teeth ja pt Tub rculo de Carabelli ... more details
A hypostatic gene is one whose phenotype is masked by the expression of an allele at a separate locus, in an epistasis event. Example In labrador retriever s, the chocolate coat colour is a result of Zygosity homozygosity for a gene that is epistasis epistatic to the black vs. yellow gene. The alleles determining whether the dog is yellow or black, are that of the hypostatic gene in this event. See also Epistasis Bombay phenotype Further reading cite book last Hartwell first Leland coauthors L. Hood, M. Goldberg, A. Reynolds, L. Silver, R. Veres title Genetics From Genes to Genomes publisher McGraw Hill date 2004 location New York, NY pages 56 57 url http highered.mcgraw hill.com sites 0072919302 information center view0 isbn 0 07 246248 5 Category Classical genetics ... more details
Unreferenced date September 2007 In Mendelian inheritance , a child receiving a dominant allele from either parent will have the dominant form of the trait. Only those that received the recessive allele from Zygosity both parents present with the recessive phenotype . Purely Mendelian traits are a tiny minority of all traits, since most phenotypic traits exhibit incomplete dominance , codominance , and quantitative trait locus contributions from many genes . Image VirgilGriffithFace.jpg thumb Attached earlobes are a recessive phenotype. Image Hitchhiker s thumbs.jpg thumb Hitchhiker s thumbs The recessive phenotype may theoretically skip any number of generations, lying dormant in Zygosity heterozygous carrier individuals until they have children with someone who also has the recessive allele and both pass it on to their child. Examples These traits include Ability to taste phenylthiocarbamide dominant Ability to smell bitter almond like hydrogen cyanide ACHOO syndrome dominant Albinism recessive Brachydactyly Shortness of fingers and toes Cleft chin dominant Free dominant or attached recessive earlobes Wet dominant or dry recessive earwax freckle Face freckles dominant Thumb Variation Hitchhiker s thumb recessive Huntingtons Disease dominant Sexdactyly Six fingers toes dominant Widow s peak allele Traits previously believed to be Mendelian Some traits were previously believed to be Mendelian, but their inheritance is probably based on more complex genetic models Fact date August 2008 , possibly involving Polygenic more than one gene . These include Eye color Hair color Morton s toe Tongue rolling See also Heritability Human genetic variation Human genetic clustering External links http www.ncbi.nlm.nih.gov omim OMIM Online Mendelian Inheritance in Man Category Genetics uk ... more details
According to Zygosity and Chorion Type A Preliminary Report. Behavior Genetics 26 407 408. ref ... in Twins According to Zygosity and Chorion Type A Preliminary Report. Behavior Genetics 26 407 408 ... membrane. The zygosity and chorion type do not influence twins handedness. ref name Derom Derom, C., Thiery, E., Vlietinck, R., Loos, R., and Derom, R. 1996. Handedness in Twins According to Zygosity ... more details
Infobox Disease Name PAGENAME Image Caption DiseasesDB 29693 ICD10 ICD10 D 58 2 d 55 ICD9 ICD9 282.7 ICDO OMIM MedlinePlus eMedicineSubj eMedicineTopic MeshID D006445 Hemoglobin C abbreviated as Hb C or HbC is an abnormal hemoglobin with substitution of a lysine residue for a glutamic acid residue at the 6th position of the globin chain. ref http www.ncbi.nlm.nih.gov entrez dispomim.cgi?id 141900&a 141900 AllelicVariant0038 Hemoglobin C HBB, GLU6LYS ref Clinical significance This mutated form reduces the normal plasticity of host erythrocytes causing a hemoglobinopathy . In those who are zygosity heterozygous for the mutation, about 28&ndash 44 of total hemoglobin Hb is HbC, and no anemia develops. In zygosity homozygotes , nearly all Hb is in the HbC form, resulting in mild hemolytic anemia . ref name pmid12818227 cite journal author Nagel RL, Fabry ME, Steinberg MH title The paradox of hemoglobin SC disease journal Blood Rev. volume 17 issue 3 pages 167 78 year 2003 month September pmid 12818227 doi 10.1016 S0268 960X 03 00003 1 url http linkinghub.elsevier.com retrieve pii S0268960X03000031 accessdate 2009 02 24 ref Presentation Codocyte Target cell s, microspherocytes and HbC crystals are found in a blood smear from a homozygous patient. Combinations with other conditions Individuals heterozygous for both HbC and Hb S Hb SC disease or for HbC and thalassemia are known, and have atypical hemolytic anemias sickle cell sickling is enhanced in Hb SC disease. Epidemiology Hemoglobin C is found predominantly in Yorubas A profile of sickle cell disease in Nigeria By O.O Akinyanju, Department of Medicine University of Lagos . It is also found in areas of West Africa, such as Ghana, where Yorubas once lived MAN Volume 56 March 1956 pages 34 36 ref name pmid12480691 cite journal author Fairhurst RM, Fujioka H, Hayton K, Collins KF, Wellems TE title Aberrant development of Plasmodium falciparum in hemoglobin CC red cells implications for the malaria protective effect of ... more details
No footnotes date April 2009 Neomorph redirects here. It is also one of the post human types of persons in the novel Eon novel Eon by Greg Bear. 1946 Nobel Prize winner Hermann J. Muller 1890 1967 coined the terms amorph, hypomorph, hypermorph, antimorph and neomorph to classify mutations based on their behaviour in various genetics genetic situations. These classifications are still widely used in Drosophila genetics to describe mutations. For a more general description of mutations, see mutation , and for a discussion of allele interactions, see dominance relationship . Key In the following sections, alleles are referred to as wildtype, m mutant, Df gene deletion, Dp gene duplication. Phenotypes are compared with > , meaning phenotype is more severe than Loss of function Amorph Amorphic describes a mutation that causes complete loss of gene function. Amorph is sometimes used interchangeably with genetic null allele null . An amorphic mutation might cause complete loss of protein function by disrupting translation protein null and or preventing transcription RNA null . An amorphic allele elicits the same phenotype when Zygosity homozygous and when zygosity heterozygous to a Genetic deletion chromosomal deletion or deficiency that disrupts the same gene. This relationship can be represented as follows m m m Df An amorphic allele is commonly dominance relationship recessive to its wildtype counterpart. It is possible for an amorph to be dominance relationship dominant if the gene in question is required in two copies to elicit a normal phenotype i.e. haploinsufficiency haploinsufficient . Hypomorph Hypomorphic describes a mutation that causes a partial loss of gene function. A hypomorph is a reduction in gene protein, RNA expression, but not a complete loss. The phenotype of a hypomorph is more severe in trans to a deletion allele than when homozygous. m Df > m m Hypomorphs are usually recessive, but occasional alleles are dominant due to haploinsufficiency . Gai ... more details
wiktionary homogeneous Homogeneity , homogeneous , or homogenization may refer to Science Homogeneity physics , translational invariance or compatibility of units in equations Homogeneous chemistry , a property of a mixture showing no variation in properties Homogenization chemistry , intensive mixing of mutually insoluble substance or groups of substance to obtain a soluble suspension or constant. Homogenized milk is one example. Homogenization biology , a process that involves breaking apart cells releasing organelles and cytoplasm Homogeneity ecology , means all of the same or similar kind or nature. In ecological terms, it can also be expressed as a lack of, or reduction in biodiversity. Homogenization mathematics , the study of partial differential equations with highly oscillatory coefficients and the determination of effective properties of materials with inhomogeneous moduli e.g. elastic, thermal, electrical Mathematics Homogenization mathematics , the study of partial differential equations with highly oscillatory coefficients Homogeneity statistics , logically consistent data matrices Homogeneous function Homogeneous polynomial , in algebra Homogeneous differential equation Linear map Homogeneous linear transformation Homogeneous coordinates , used in projective spaces Homogeneous space for a Lie group G, or more general transformation group Graded algebra Homogeneous ideal in a graded ring Homogeneous large cardinal property Homogeneous model in model theory Homoscedasticity , homogeneity of variance See also Heterogeneous disambiguation , links relating to objects or systems consisting of multiple items having a large number of structural variations Monoculturalism , ethnic homogeneity or the advocacy of it Zygosity disambig bg cs Homogenita eo Homogeneco fr Homog n it it Omogeneit nl Homogeniteit pt Homogeneidade ru sk Homogenita sl Homogenost ... more details
heredity outcomes A the affected father has one X linked dominant allele, the mother is Zygosity ... is Zygosity Hemizygous hemizygous with one copy of the X linked dominant allele both daughters ... more details
in the zygosity heterozygous individuals in populations of ploidy diploid organisms recessive alleles are only expressed in the less common zygosity homozygous individuals . Natural selection can also ... more details
degree. ref name Dun Zygosity http www.vgl.ucdavis.edu services dunhorse.php Dun Zygosity ... visible on horses with a short summer coat. ref name Dun Zygosity Taxonomic distribution Seealso .... Web Site accessed January 12, 2008 http www.vgl.ucdavis.edu services dunhorse.php Dun Zygosity test ... more details
Thelytoky comes from the Greek language Greek thely, meaning female , and tok, meaning birth . Thelytokous parthenogenesis is a type of parthenogenesis in which females are produced from unfertilized eggs. It is rare in the animal animal kingdom and has only been reported in about 1500 species . ref White, M 1984 . Chromosomal mechanisms in animal reproduction. Bull Zoology 51 1 23. ref It is more common in invertebrates , like arthropods , but can also occur in vertebrates , like some Cnemidophorus whiptail lizards . Thelytoky can occur by a number of different mechanisms each of which has a different impact on the level of zygosity homozygosity . It can be induced in Hymenoptera by the bacteria Wolbachia and Cardinium ref Jeong, G. and Stouthamer, R. 2005 Genetics of female functional virginity in the Parthenogenesis Wolbachia infected parasitoid wasp Horntail Telenomus nawai Hymenoptera Scelionidae . Heredity 94 402 407 ref , and has also been described in several groups of Hymenoptera, including Cynipidae , Tenthredinidae , Aphelinidae , Ichneumonidae , Apidae and Formicidae . ref Suomalainen E, Saura A, Lokki J 1987 . Cytology and Evolution in Parthenogenesis. CRC Press Inc. Boca Raton, FL. ref Hymenoptera ant s, bee s and wasp s usually reproduce by arrhenotoky arrhenotokous parthenogenesis . They have the haplodiploid sex determination system , and usually unfertilized eggs develop into haploid males, and fertilized eggs develop into diploid females. In thelytoky, however, female worker bee worker s or queen insect queen s are produced by laying worker bee s when diploidy is restored in their eggs by the fusion of two meiosis meiotic products. ref Baudry, E. et al. 2004 Whole Genome Scan in Thelytokous Laying Workers of the Cape Honey bee Apis mellifera capensis Central Fusion, Reduced Recombination Rates and Centromere Mapping Using Half Tetrad Analysis. Genetics journal 167 243 252 ref . These laying workers are therefore producing unfertilized diploid eggs ... more details
H1299 , also known as National Cancer Institute NCI H1299 ref name pmid8965489 cite journal author title NCI Navy Medical Oncology Branch cell line supplement journal J. Cell. Biochem. Suppl. volume 24 issue pages 1 291 year 1996 pmid 8965489 doi url issn ref ref name ATCC The Global Biosource Center cite web url http www.atcc.org ATCCAdvancedCatalogSearch ProductDetails tabid 452 Default.aspx?ATCCNum CRL 5803&Template cellBiology title ATCC Advanced Catalog Search author authorlink coauthors date format work publisher pages language archiveurl archivedate quote accessdate 2009 01 07 ref or CRL 5803 , ref name urlLGC Promochem Cell Biology Collection cite web url http www.atcc.org ATCCAdvancedCatalogSearch ProductDetails tabid 452 Default.aspx?ATCCNum CRL 5803&Template cellBiology title CRL 5803 NCI H1299 cell line author authorlink coauthors date format work LGC Promochem Cell Biology Collection publisher American Type Culture Collection pages language archiveurl archivedate quote accessdate 2008 06 22 ref is a non small cell lung carcinoma cell line derived from the lymph node, which is widely used in research. ref name pmid1563005 cite journal author Giaccone G, Battey J, Gazdar AF, Oie H, Draoui M, Moody TW title Neuromedin B is present in lung cancer cell lines journal Cancer Res. volume 52 issue 9 Suppl pages 2732s 2736s year 1992 month May pmid 1563005 doi url http cancerres.aacrjournals.org cgi content abstract 52 9 Supplement 2732s issn ref As with other biological immortality immortalized cell lines, H1299 cells can divide indefinitely. These cells have a zygosity Homozygous homozygous partial deletion of the TP53 gene and as a result, do not express the tumor suppressor p53 protein which in part accounts for their cell growth proliferative propensity. ref name pmid8663350 cite journal author Lin DL, Chang C title p53 is a mediator for radiation repressed human TR2 orphan receptor expression in MCF 7 cells, a new pathway from tumor suppressor to member of ... more details
Infobox disease Name Fabry disease ICD10 ICD10 E 75 2 e 70 ILDS E75.25 ICD9 ICD9 272.7 ICDO Image PBB Protein GLA image.jpg Caption Alpha galactosidase the protein that is deficient in Fabry disease . OMIM 301500 OMIM mult MedlinePlus eMedicineSubj neuro eMedicineTopic 579 eMedicine mult eMedicine2 derm 707 eMedicine2 ped 2888 DiseasesDB 4638 MeshID D000795 Fabry disease also known as Fabry s disease , Anderson Fabry disease , angiokeratoma corporis diffusum and alpha galactosidase A deficiency is a rare X linked recessive inherited lysosomal storage disease , which can cause a wide range of systemic symptoms. ref name Andrews Cite book author James, William D. Berger, Timothy G. et al. title Andrews Diseases of the Skin clinical Dermatology publisher Saunders Elsevier location year 2006 page 538 isbn 0 7216 2921 0 oclc doi accessdate ref The disease is named after one of its discoverers, Johannes Fabry. ref WhoNamedIt synd 1761 ref Pathophysiology A deficiency of the enzyme alpha galactosidase alpha galactosidase A a GAL A, encoded by http www.genenames.org data hgnc data.php?match GLA GLA due to mutation causes a glycolipid known as globotriaosylceramide abbreviated as Gb3, GL 3, or ceramide trihexoside to accumulate within the blood vessel s, other tissues, and organs. ref name pmid16403380 Cite journal author Karen JK, Hale EK, Ma L title Angiokeratoma corporis diffusum Fabry disease journal Dermatol. Online J. volume 11 issue 4 pages 8 year 2005 pmid 16403380 doi url http dermatology.cdlib.org 114 NYU NYUtexts 0419054.html ref This accumulation leads to an impairment of their proper function. The DNA mutations which cause the disease are X linked recessive . The condition affects Zygosity hemizygous males i.e. all males , as well as Zygosity homozygous , and in many cases Zygosity heterozygous females. While males typically experience severe symptoms, women can range from being asymptomatic to having severe symptoms. This variability is thought to be due to X i ... more details
If two alleles of a given gene are identical, the organism is called a zygosity homozygote and is homozygous with respect to that gene if instead the two alleles are different, the organism is a zygosity ... their phenotype when present in the zygosity heterozygous ... state. ref Which trait is dominant ? The terms ... X chromosome gene locus, and are described as zygosity hemizygous for these genes. The Y chromosome ... more details
Improveref date February 2010 For the musician nicknamed Big Toe Big Toe musician Infobox Anatomy Name PAGENAME Latin Hallux Digitus primus pedis GraySubject GrayPage Image RightFootToes.jpg Caption The innermost toe left in image is the hallux. Precursor System Artery Vein Nerve Lymph MeshName MeshNumber In tetrapod s, the hallux big toe , great toe is the innermost most Anatomical terms of location Left and right lateral , and medial medial toe of the foot . Despite its name it may not be the longest toe on the foot of some individuals. It is counted as digit I one . The name stems from the Latin for the same, similar to the pollex , which refers to the thumb , the corresponding digit of the hand . People who go barefoot or wear open toed sandals most of the time tend to have have big toes that are separate from the others, whereas in persons who wear shoes most of the time, the big toes are squeezed toward touching the second toes. Digit ratio see also Digit ratio In human s, the hallux is longer than the second or pointer or index toe for a majority of people. This is an Mendelian inheritance inherited trait in humans, where the Dominance genetics dominant gene causes a longer second toe Morton s toe or Greek foot while the Zygosity homozygous recessive genotype presents with the more common trait a longer hallux. ref OMIM 189200 Toes relative lengths of first and second ref People with the rare genetic disease fibrodysplasia ossificans progressiva characteristically have a short hallux which appears to turn inward, or medially, in relation to the foot. In bird s with anisodactyl or heterodactyl feet, the hallux is opposed or directed backwards and allows for grasping and perching . Evolution While the thumb is often mentioned as the one of the signature characteristics in humans, this manual digit remains partially primitive and is actually present in all primates . In humans, the most derived digital feature is the hallux. ref cite journal ref harv last1 ... more details
A heterozygote advantage heterozygous advantage describes the case in which the Zygosity heterozygote genotype has a higher relative fitness biology fitness than either the Zygosity homozygote Dominance genetics dominant or homozygote recessive gene recessive genotype . This selection favoring the heterozygote is one of the mechanisms that maintain Polymorphism biology polymorphism and help to explain some kinds of genetic variation genetic variability . There are several cases in which the heterozygote conveys certain advantages and some disadvantages while both versions of homozygotes are only at disadvantages. A well established case of heterozygote advantage is that of the gene involved in sickle cell disease sickle cell anaemia . Often, the advantages and disadvantages conveyed are rather complicated, because more than one gene may influence a given Phenotypic trait trait or Polymorphism biology morph . Major gene s almost always have multiple effects Pleiotropy pleiotropism , which can simultaneously convey separate advantageous traits and disadvantageous traits upon the same organism. In this instance, the state of the organism s environment will provide selection , with a net effect either favoring or working in opposition to the gene, until an environmentally determined equilibrium is reached. Heterozygote advantage in theory When two populations of any sexual organism are separated and kept isolated from each other, the frequencies of deleterious mutations in the two populations will differ over time, by genetic drift . It is highly unlikely, however, that the same deleterious mutations will be prevalent in both populations after a long period of separation. Since loss of function mutations tend to be recessive given that dominant mutations of this type generally ... . Other mutations, which inactivate the enzyme null allele s are lethal when inherited Zygosity homozygous ly two defect copies of the TPI gene , but have no obvious effect as Zygosity heterozygotes ... more details
Infobox Disease Name Bazex Dupre Christol syndrome Image Caption DiseasesDB 34543 ICD10 ICD9 ICDO OMIM 301845 MedlinePlus eMedicineSubj eMedicineTopic MeshID Bazex Dupre Christol syndrome also known as Bazex syndrome, ref name Bolognia and Follicular atrophoderma and basal cell carcinomas ref name Bolognia cite book author Rapini, Ronald P. Bolognia, Jean L. Jorizzo, Joseph L. title Dermatology 2 Volume Set publisher Mosby location St. Louis year 2007 pages isbn 1 4160 2999 0 oclc doi accessdate ref is a very rare condition inherited in an X linked dominant fashion. Physical findings typically include follicular atrophoderma , multiple basal cell carcinoma s, hypotrichosis and hypohidrosis . ref Bolognia,J 2008 Dermatology , Mosby, ISBN 9781416029991. ref This condition should not be confused with the unrelated condition Acrokeratosis paraneoplastica of Bazex , which may also be referred to Bazex syndrome. Genetics Double image right Xlink dominant mother.jpg 185 X link dominant father.jpg 185 X linked dominant inheritance works differently depending upon whether the mother left image or father right image is the carrier of a gene that causes a disease or disorder BCDS is inherited in an X linked dominant manner. This means the defective gene responsible for the disorder is located on the X chromosome, and only one copy of the defective gene is sufficient to cause the disorder when inherited from a parent who has the disorder. Males are normally Zygosity Hemizygous hemizygous for the X chromosome, having only one copy. As a result, X linked dominant disorders usually show higher expressivity in males than females. As the X chromosome is one of the sex chromosome s the other being the Y chromosome , X linked inheritance is determined by the gender of the parent carrying a specific gene and can often seem complex. This is because, typically, female s have two copies of the X chromosome, while male s have only one copy. The difference between Dominance genetics Dominan ... more details
Image Placentation.svg thumb 300px Various types of chorionicity and amniosity how the baby s sac looks in monozygotic one egg identical twins as a result of when the fertilized egg divides Monochorionic twins are monozygotic identical twins that share the same placenta . If the placenta is shared by more than two twins see multiple birth , these are monochorionic multiples . Monochorionic twins occur in 0.3 of all pregnancies. ref name cordero cite journal author Cordero L, Franco A, Joy SD, O shaughnessy RW title Monochorionic diamniotic infants without twin to twin transfusion syndrome journal J Perinatol volume 25 issue 12 pages 753 8 year 2005 month December pmid 16281049 doi 10.1038 sj.jp.7211405 url ref 75 of monozygotic twin pregnancies are monochorionic the remaining 25 are dichorionic diamniotic . ref name Shulman If the placenta divides, this takes place after the third day after fertilization . ref name Shulman cite book author Shulman, Lee S. Vugt, John M. G. van title Prenatal medicine publisher Taylor & Francis location Washington, DC year 2006 pages Page 447 isbn 0 8247 2844 0 oclc doi accessdate ref Amniocity and zygosity Monochorionic twins generally have two amniotic sac s called Monochorionic Diamniotic MoDi , but sometimes, in the case of monoamniotic twins Monochorionic Monoamniotic MoMo , they also share the same amniotic sac. Monoamniotic twins occur when the split takes place after the ninth day after fertilization. ref name Shulman Monoamniotic twins are always monozygotic identical twins . ref name pregnancy info http www.pregnancy info.net monoamniotic.html Pregnancy Info Monoamniotic Twins Retrieved on July 9, 2009 ref Monochorionic Diamniotic twins are almost always monozygotic, with a few exceptions where the blastocysts have fused. ref name Shulman Complications In addition to a shared placenta, monochorionic twins also have their circulatory system s intermingled in random and unpredictable circulatory anastomoses . This can cause di ... more details
dablink This article is not about F statistics as that term is understood in statistical inference, especially analysis of variance and linear regression. See F test F test and F distribution F distribution . In population genetics , F statistics also known as fixation indices describe the level of Zygosity heterozygosity in a population more specifically the degree of usually a reduction in heterozygosity when compared to Hardy&ndash Weinberg law Hardy&ndash Weinberg expectation . F statistics can also be thought of as a measure of the correlation between genes drawn at different levels of a hierarchically subdivided population. This correlation is influenced by several evolutionary processes, such as mutation, migration, inbreeding , natural selection , or the Wahlund effect , but it was originally designed to measure the amount of allelic fixation owing to genetic drift. The concept of F statistics was developed during the 1920s by the United States American geneticist Sewall Wright , who was interested in inbreeding in cattle . However, because complete dominance causes the phenotype s of Zygosity homozygote dominants and heterozygotes to be the same, it was not until the advent of molecular genetics from the 1960s onwards that heterozygosity in populations could be measured. Definitions and equations The measures F sub IS sub , Fixation index F sub st sub , and F sub IT sub are related to the amounts of heterozygosity at various levels of population structure. Together, they are called F statistics, and are derived from F , the inbreeding coefficient. In a simple two allele system with inbreeding, the genotypic frequencies are math p 2 1 F pF text for mathbf AA 2pq 1 F text for mathbf Aa text and q 2 1 F qF text for mathbf aa . math The value for F is found by solving the equation for F using heterozygotes in the above inbred population. This becomes one minus the observation observed number of heterozygotes in a population divided by its expected value expecte ... more details
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