Please explain the terms "homozygous" and "heterozygous".? | Yahoo Answers
E-mail: [email protected] However, heterozygosity for the CY/ H63D is defined in many screening studies without any clinical importance, which. Main · Videos; Alappuzha district panchayat tenders dating heterozygous definition yahoo dating heterozygous definition yahoo dating makro racer review uk. Yozgat, Turkey, Tel: + , Email: [email protected] Received Date: Mar 27, / Accepted Date: Apr 09, / Published Date: Apr 15, Wild, heterozygous and homozygous genotypic distributions of these .. a less well-defined effect, with a lesser decrease of the enzymatic activity .
It is unknown if iron deposits in target organs precede or parallel to the elevation in serum studies, or the possibility that joint damage in patients with HFE mutations is independent of iron perhaps due to as-yet unidentified immunological effects of the HFE mutations cannot be excluded [ 12 ]. The iron overload is still the corner stone in the diagnosis, but elevation in serum iron studies could be delayed and does not reflect the damage degree of end organ.
The clinical correlation with genetic test is required especially in unknown as-yet unidentified immunological etiology of arthropathy which is still the most presentation of compound heterozygotes of hemochromatosis. In many articles, the diagnosis of hereditary hemochromatosis requires increased iron stores, with or without symptoms. CY homozygosity in the absence of elevated iron stores is not diagnostic for hereditary hemochromatosis. The genetic test is ordered to confirm the diagnosis in patient with clinical presentation and high iron studies.
However this recommendation may be reconsidered, HFE mutation analysis should be performed in a case such as our case where arthropathy presented as atypical arthritis with mild or even normal upper limit of iron studies, further studies may be needed. Negative iron studies are used to rule out the disease in children who have one parent with hereditary hemochromatosis if the other parent does not have it [ 11 ].
Additionally, an elevated serum ferritin level is not diagnostic for hereditary hemochromatosis [ 7 ]. However, serum ferritin value is still the most important prognostic test in patients with homozygous hemochromatosis: And avoid unnecessary liver biopsy used usually to determine the degree of fibrosis or cirrhosis.
Is there another indicator of hemochromatosis? Noninvasive specialized magnetic resonance imaging MRI techniques may be used to determine the degree of hepatic iron content or to diagnose nonclassical hemochromatosis in patients with CY heterozygosity and severely elevated ferritin levels [ 3 ]. There is no data to use it in patients without elevated ferritin. The frequency of phlebotomy is guided by serial measurements of serum ferritin levels and transferring saturation in hereditary hemochromatosis with a goal of 50 to ng per mL Facing of this challenge should be taken to try to prevent complications which sometimes even with treatment will not be reversible such as established cirrhosis or significantly arthropathy, testicular atrophy, or thyroid dysfunction [ 3 ].
All the offspring form this patient will be carrier and other family members are at increased risk. Even there is no official recommendation but genetic counseling and HH molecular testing are recommended for at risk family member.
Equal numbers of gametes, ovules, or pollen grains are formed that contain the genes R and r. The white-flowered plants, which must be recessive homozygotes, bear the genotype rr. Mendel's law of independent assortment. Cross of peas having yellow and smooth … Mendel also crossbred varieties of peas that differed in two or more easily distinguishable traits. When a variety with yellow round seed was crossed to a green wrinkled seed variety Figure 2the F1 generation hybrids produced yellow round seed.
Evidently yellow A and round B are dominant traits, green a and wrinkled b are recessive. By allowing the F1 plants genotype AaBb to self-pollinate, Mendel obtained an F2 generation of yellow round, yellow wrinkled, green round, and 32 green wrinkled seeds, a ratio approximately 9: The important point here is that the segregation of the colour A—a is independent of the segregation of the trait of seed surface B—b.
This is expected if the F1 generation produces equal numbers of four kinds of gametes, carrying the four possible combinations of the parental genes: AB, Ab, aB, and ab. Random union of these gametes gives, then, the four phenotypes in a ratio 9 dominant—dominant: Among these four phenotypic classes there must be nine different genotypes, a supposition that can be tested experimentally by raising a third hybrid generation.
The predicted genotypes are actually found. Another test is by means of a backcross or testcross —the F1 hybrid phenotype yellow round seed; genotype AaBb is crossed to a double recessive plant phenotype green wrinkled seed; genotype aabb. If the hybrid gives four kinds of gametes in equal numbers and if all the gametes of the double recessive are alike abthe predicted progeny of the backcross are yellow round, yellow wrinkled, green round, and green wrinkled seed in a ratio 1: This prediction is realized in experiments.
The second generation of hybrids, the F2, has 27 33 genotypically distinct kinds of individuals but only eight different phenotypes. From these results and others Mendel derived his second law, the law of recombination or independent assortment of genes.
Please explain the terms "homozygous" and "heterozygous".?
Universality of Mendel's laws Although Mendel experimented with varieties of peas, his laws have been shown to apply to the inheritance of many kinds of characters in almost all organisms. In Mendelian inheritance was demonstrated in poultry and in mice. The following year, albinism became the first human trait shown to be a Mendelian recessive, with pigmented skin the corresponding dominant. In and Sir Archibald Garrod initiated the analysis of inborn errors of metabolism in humans in terms of biochemical genetics.
Alkaptonuria, inherited as a recessive, is characterized by excretion in the urine of large amounts of the substance called alkapton, or homogentisic acid, which renders the urine black on exposure to air. Garrod advanced the hypothesis that this enzyme is absent or inactive in homozygous carriers of the defective recessive alkaptonuria gene; hence the homogentisic acid accumulates and is excreted in the urine. Mendelian inheritance of numerous traits in humans has been studied since then.
In analyzing Mendelian inheritance, it should be borne in mind that an organism is not an aggregate of independent traits, each determined by one gene. One gene may affect many traits a condition termed pleiotropic. The gene white in Drosophila flies is pleiotropic; it affects the colour of the eyes and of the testicular envelope in the males, the fecundity and the shape of the spermatheca in the females, and the longevity of both sexes. In humans many diseases caused by a single defective gene will have a variety of symptoms, all pleitropic manifestations of the gene.Yahoo Answers Cringe: Vol. 1
Allelic interactions Dominance relationships The operation of Mendelian inheritance is frequently more complex than in the case of the traits recorded by Mendel. In the first place, clear-cut dominance and recessiveness are by no means always found. When red- and white-flowered varieties of four-o'clock plants or snapdragons are crossed, for example, the F1 hybrids have flowers of intermediate pink or rose colour, a situation that seems more explicable by the blending notion of inheritance than by Mendelian concepts.
That the inheritance of flower colour is indeed due to Mendelian mechanisms becomes apparent when the F1 hybrids are allowed to cross, yielding an F2 generation of red- pink- and white-flowered plants in a ratio of 1 red: Obviously the hereditary information for the production of red and white flowers had not been blended away in the first hybrid generation, as flowers of these colours were produced in the second generation of hybrids.
The apparent blending in the F1 generation is explained by the fact that the gene alleles that govern flower colour in four-o'clocks show an incomplete dominance relationship. Suppose, then, that a gene allele R1 is responsible for red and R2 for white flowers; the homozygotes R1R1 and R2R2 are red and white respectively, and the heterozygotes R1R2 have pink flowers.
A similar pattern of lack of dominance is found in shorthorn cattle. In diverse organisms, dominance ranges from complete a heterozygote indistinguishable from one of the homozygotes through incomplete heterozygotes exactly intermediate to excessive or over-dominance a heterozygote more extreme than either homozygote.
Another form of dominance is one in which the heterozygote displays the phenotypic characteristics of both alleles. This is called codominance; an example is seen in the MN blood group system of human beings. MN blood type is governed by two alleles, M and N.
Individuals who are homozygous for the M allele have a surface molecule called the M antigen on their red blood cells. Similarly, those homozygous for the N allele have the N antigen on the red blood cells. Heterozygotes—those with both alleles—carry both antigens. Multiple alleles The traits discussed so far all have been governed by the interaction of two possible alleles. Many genes, however, are represented by multiple allelic forms within a population.
One individual, of course, can possess only two of these multiple alleles. Human blood groups—in this case, the well-known ABO system—again provide an example.
The gene that governs ABO blood types has three alleles: Because of the multiple alleles and their various dominance relationships, there are four phenotypic ABO blood types: Gene interactions Many individual traits are affected by more than one gene.
For example, the coat colour in many mammals is determined by numerous genes interacting to produce the result. The great variety of colour patterns in cats, dogs, and other domesticated animals is the result of different combinations of complexly interacting genes. The gradual unravelling of their modes of inheritance was one of the active fields of research in the early years of genetics.
Two or more genes may produce similar and cumulative effects on the same trait. In humans, the skin colour difference between so-called blacks and so-called whites is due to several probably four or more interacting pairs of genes, each of which increases or decreases the skin pigmentation by a relatively small amount.
Epistatic genes Some genes mask the expression of other genes just as a fully dominant allele masks the expression of its recessive counterpart. The gene that masks the phenotypic effect of another gene is called the epistatic gene; the gene it subordinates is the hypostatic gene. The gene for albinism lack of pigment in humans is an epistatic gene.
It is not part of the interacting skin-colour genes described above; rather, its dominant allele is necessary for the development of any skin pigment, and its recessive homozygous state results in the albino condition regardless of how many other pigment genes may be present. Albinism thus occurs in some individuals among people who belong to the dark- or intermediate-pigmented races, such as blacks and American Indians, as well as among whites.
The presence of epistatic genes explains much of the variability seen in the expression of such dominantly inherited human diseases as Marfan's syndrome and neurofibromatosis. Because of the effects of an epistatic gene, some individuals who inherit the dominant, disease-causing gene show only partial symptoms of the disease; some, in fact, may show no expression of the disease-causing gene, a condition referred to as nonpenetrance.
The individual in whom such a nonpenetrant mutant gene exists will be phenotypically normal but still capable of passing the deleterious gene on to offspring, who may exhibit the full-blown disease. Examples of epistasis abound in nonhuman organisms. In mice, as in humans, the gene for albinism has two variants: The latter allele is unable to synthesize the pigment melanin.
Mice, however, have another pair of alleles involved in melanin placement. These are the agouti allele, which produces dark melanization of the hair except for a yellow band at the tip, and the black allele, which produces melanization of the whole hair. If melanin cannot be formed the situation in the mouse homozygous for the albino gene neither agouti nor black can be expressed.
Complementation The phenomenon of complementation is another form of interaction between nonallelic genes.
Iron Study is a Weak Indicator in Symptomatic C282Y/ H63D Compound Heterozygotes
For example, there are mutant genes that in the homozygous state produce profound deafness in humans. One would expect that the children of two persons suffering from such hereditary deafness would all be deaf.
This is frequently not the case, because the parents' deafness is often caused by different genes. Since the mutant genes are not alleles, the child becomes heterozygous for the two genes and hears normally. In other words, the two mutant genes complement each other in the child. Complementation thus becomes a test for allelism.
In the case of congenital deafness cited above, if all the children had been deaf, one could assume that the deafness in each of the parents was due to mutant genes that were alleles.
This would be more likely to occur if the parents were genetically related consanguineous. Polygenic inheritance The greatest difficulties of analysis and interpretation are presented by the inheritance of many quantitative or continuously varying traits.
Inheritance of this kind produces variations in degree rather than in kind, in contrast to the inheritance of discontinuous traits resulting from single genes of major effect see above. The yield of milk in different breeds of cattle, egg-laying capacity in poultry, and stature, shape of the head, blood pressure, and intelligence in humans range in continuous series from one extreme to the other and are significantly dependent on environmental conditions.
Crosses of two varieties differing in such characters usually give F1 hybrids intermediate between the parents. That Mendelian segregation does take place with polygenes, as with the genes having major effects sometimes called oligogenesis shown by the variation among F2 and further generation hybrids being usually much greater than that in the F1 generation.
By selecting among the segregating progenies the desired variants, for example, individuals or families with the greatest yield, the best size, or a desirable behaviour, it is possible to produce new breeds or varieties sometimes exceeding the parental forms. Hybridization and selection are consequently potent methods that can be used for improvement of agricultural plants and animals.
Polygenic inheritance also applies to many of the birth defects congenital malformations seen in humans. Although expression of the defect itself may be discontinuous as in clubfoot, for examplesusceptibility to the trait is continuously variable and follows the rules of polygenic inheritance.
When a developmental threshold produced by a polygenically inherited susceptibility and a variety of environmental factors is exceeded, the birth defect results. Heredity and environment Preformism and epigenesis A notion that was widespread among pioneer biologists in the 18th century was that the fetus, and hence the adult organism that develops from it, is preformed in the sex cells.
The development of the individual from the sex cells appeared deceptively simple—it was merely increase in size and growth of what was already present in the sex cells. The antithesis of the early preformation theories were theories of epigenesis, which claimed that the sex cells were structureless jelly and contained nothing at all in the way of rudiments of future organisms.
The naive early versions of preformation and epigenesis had to be given up when embryologists showed that the embryo develops by a series of complex but orderly and gradual transformations see animal development. Heredity has been defined as a process that results in the progeny's resembling their parents.
A further qualification of this definition states that what is inherited is a potential that expresses itself only after interacting with and being modified by environmental factors. In short, all phenotypic expressions have both hereditary and environmental components, the amount of each varying for different traits. Thus, a trait that is primarily hereditary e. And conversely, a trait sensitive to environmental modifications e.
Organic development is preformistic insofar as a fertilized egg cell contains a genotype that conditions the events that may occur and is epigenetic insofar as a given genotype allows a variety of possible outcomes.
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- The incidence of FVL and PT G20210A mutations in patients with idiopathic deep venous thrombosis
These considerations should dispel the reluctance felt by many people to accept the fact that mental as well as physiological and physical traits in humans are genetically conditioned. Heritability Although hereditary diseases and malformations are, unfortunately, by no means uncommon in the aggregate, no one of them occurs very frequently.
The characteristics by which one person is distinguished from another, such as facial features, stature, shape of the head, skin, eye and hair colours, and voice, are not usually inherited in a clear-cut Mendelian manner, as are some hereditary malformations and diseases. This is not as strange as it may seem. The kinds of gene changes, or mutations, that produce morphological or physiological effects drastic enough to be clearly set apart from the more usual phenotypes are likely to cause diseases or malformations just because they are so drastic.
The variations that occur among healthy persons are, as a general rule, caused by polygenes with individually small effects. The same is true of individual differences among members of various animal and plant species. Even brown-blue eye colour in humans, which in many families behaves as if caused by two forms of a single gene brown being dominant and blue recessiveis often blurred by minor gene modifiers of the pigmentation.
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Some apparently blue-eyed persons actually carry the gene for the brown eye colour, but several additional modifier genes decrease the amount of brown pigment in the iris. This type of genetic process can influence susceptibility to many diseases e. The question geneticists must often attempt to answer is how much of the observed diversity between persons, or between individuals of any species, is due to hereditary, or genotypic, variations and how much of it is due to environmental influences.
Applied to human beings, this is sometimes referred to as the nature—nurture problem. With animals or plants the problem is evidently more easily soluble than it is with people. Two complementary approaches are possible.
First, individual organisms, or their progenies, are raised in environments as uniform as can be provided, with food, temperature, light, humidity, etc. The differences that persist between such individuals or progenies probably reflect genotypic differences. Second, individuals with similar or identical genotypes are placed in different environments. The phenotypic differences then may be ascribed to environmental induction. Experiments combining both approaches have been carried out on several species of plants that grow naturally at different altitudes, from sea level to the alpine zone of the Sierra Nevada of California.
Young yarrow plants Achillea were cut in three parts and the cuttings replanted in experimental gardens at sea level, at midaltitude 4, feet [1, metres]and at a high altitude 10, feet [3, metres]. The plants native at sea level grow best in their native habitat, grow less well at midaltitudes, and die at high altitudes. On the other hand, the alpine race survives and develops better at the high-altitude transplant station than it does at lower altitudes. With organisms that cannot survive being cut in pieces and placed in controlled environments, a partitioning of the observed variability into genetic and environmental components may be attempted by other methods.
Suppose that in a certain population individuals vary in stature, weight, or some other trait. These characters can be measured in many pairs of parents and in their progenies raised under different environmental conditions. On the other hand, if the environment is unimportant and the character is uncomplicated by dominance, then the means of this character in the progenies will be the same as the means of the parents; with differences in the expression in females and in males taken into account, the heritability will equal unity.
In reality, most heritabilities are found to lie between zero and one. Some examples of heritabilities of traits in different animals are given in Table 2. It is important to understand clearly the meaning of heritability estimates.
They show that, given the range of the environments in which the experimental animals lived, one could predict the average body sizes in the progenies of pigs better than one could predict the average numbers of piglets in a litter. The heritability is, however, not an inherent or unchangeable property of each character. If one could make the environments more uniform, the heritabilities would rise, and with more diversified environments they would decrease.
Combination of acquired risk factors with inherited genetic factors significantly increases the risk of thrombosis [ 16 ]. Although FVL leads to an increased risk of VTE, many carriers of FVL may not show clinical findings of thrombosis unless they have combined risk factors, such as deficiency of protein C or protein S [ 17 ].
In certain subgroups that are already at increased risk for thrombosis patients taking birth control pill, patients with hereditary protein C deficiencythe added presence of FVL may have a multiplicative effect on thrombophilic risk [ 18 ].
Women taking birth control pill who had FVL were found to have a fold increase in risk for venous thrombosis compared with women who had no risk factor [ 18 ]. Carrier status of both FVL and PT GA may be advantageous to fertile females, reducing gynecologic hemorrhage, and protecting against anemia [ 1920 ].
Also these polymorphisms may have been protective in the past, particularly in times when hunting-related injury was more common and medical management rather primitive [ 19 ]. Although these conditions seemed to be useful during Neolithic period, we think that these polymorphisms may be harmful at the present time owing to severe thromboembolic complications.
PT GA polymorphism has been found to be associated with increased level of prothrombin known as a risk factor for thrombosis [ 7 ]. Similar to FVL mutation, its prevalence has also been detected high in white population of European origin [ 21 ]. These mutations are associated with high risk of DVT [ 23 ]. The prevalence of PT GA mutation was detected as 2.
PT GA mutation was found as 8. Thus, these patients should be candidates for lifelong anticoagulant treatment [ 26 ]. Carriers of heterozygous or homozygous FVL polymorphism have a thrombophilic tendency that may be enhanced during an inflammatory condition [ 27 ]. Although venous thrombosis is thought major clinical manifestation of the FVL, there is also evidence that FVL may play a role leading to unrecognized miscarriage due to thrombosis of placental vessels [ 5 ].
Therefore, screening of both polymorphisms might be recommended for women with a history of recurrent miscarriage. Especially, the homozygous MTHFR CT polymorphism may lead to decreased enzymatic activity and increased homocysteinemia levels, whereas the MTHFR AC polymorphism presents a less well-defined effect, with a lesser decrease of the enzymatic activity [ 29 ]. The resultant mild hyperhomocysteinemia observed in homozygotes for MTHFR TT genotype is accentuated when such patients have reduced plasma folic acid levels [ 30 ].
The relation between the risk of venous thrombosis and hyperhomocysteinemia is not clear. Homocysteine is likely to produce a thrombogenic effect by damaging the vascular endothelial cells [ 17 ]. During the past decade, epidemiologic studies have showed that mild to moderate homocysteinemia as an independent risk factor for VTE [ 21 ]. For this reason investigation of these mutations will be particularly helpful in adjusting the duration of anticoagulant therapy in patients with DVT.
However, our study should be continued by increasing the number of subjects and supported by further studies. J Hematol Transfus Med ; Genetic mutations in Turkish population with pulmonary embolism and deep venous thrombosis. Clin Appl Thromb Hemost ; Frequency of genetic mutations associated with thromboembolism in the western black sea region.