|
X-linked
Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, X-linked dominant and Y-linked. The inheritance and presentation of all three differ depending on the sex of both the parent and the child. This makes them characteristically different from autosomal dominance and recessiveness. There are many more X-linked conditions than Y-linked conditions, since humans have several times as many genes on the X chromosome than the Y chromosome. Only females are able to be carriers for X-linked conditions; males will always be affected by any X-linked condition, since they have no second X chromosome with a healthy copy of the gene. As such, X-linked recessive conditions affect males much more commonly than females. In X-linked recessive inheritance, a son born to a carrier mother and an unaffected f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-linked Dominant
X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome. As an inheritance pattern, it is less common than the X-linked recessive type. In medicine, X-linked dominant inheritance indicates that a gene responsible for a genetic disorder is located on the X chromosome, and only one copy of the allele is sufficient to cause the disorder when inherited from a parent who has the disorder. In this case, someone who expresses an X-linked dominant allele will exhibit the disorder and be considered affected. X-linked dominant traits do not necessarily affect males more than females (unlike X-linked recessive traits). The exact pattern of inheritance varies, depending on whether the father or the mother has the trait of interest. All fathers that are affected by an X-linked dominant disorder will have affected daughters but not affected sons. However, if the mother is also affec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-linked Recessive
X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily homozygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation, see zygosity. Females with one copy of the mutated gene are carriers. X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes while males have one X and one Y chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X-chromosome inactivation (known as skewed X-inactivation) can lead to varying degrees of clinical expression in carrier females, since some cells will express one X allele and some will express the other. The current estimate of sequenced X-linked genes is 499, and the total, including vaguely defined trait ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex-linked Inheritance
Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, X-linked dominant and Y-linked. The inheritance and presentation of all three differ depending on the sex of both the parent and the child. This makes them characteristically different from autosomal dominance and recessiveness. There are many more X-linked conditions than Y-linked conditions, since humans have several times as many genes on the X chromosome than the Y chromosome. Only females are able to be carriers for X-linked conditions; males will always be affected by any X-linked condition, since they have no second X chromosome with a healthy copy of the gene. As such, X-linked recessive conditions affect males much more commonly than females. In X-linked recessive inheritance, a son born to a carrier mother and an unaffected fa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-inactivation
X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into a transcriptionally inactive structure called heterochromatin. As nearly all female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome (see dosage compensation). The choice of which X chromosome will be inactivated in a particular embryonic cell is random in placental mammals such as humans, but once an X chromosome is inactivated it will remain inactive throughout the lifetime of the cell and its descendants in the organism (its cell line). The result is that the choice of inactivated X chromosome in all the cells of the organism is a random distribution, often with about half the cells having the paternal X chromosom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X Chromosome
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), 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 object and consequently named it ''X element'', which later ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skewed X-inactivation
Skewed X-chromosome inactivation (skewed X-inactivation) occurs when the X-inactivation of one X chromosome is favored over the other, leading to an uneven number of cells with each chromosome inactivated. It is usually defined as one allele being found on the active X chromosome in over 75% of cells, and extreme skewing is when over 90% of cells have inactivated the same X chromosome. It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or by secondary nonrandom inactivation, which occurs by selection. X-chromosome inactivation occurs in females to provide dosage compensation between the sexes. If females kept both X chromosomes active, they would have twice the number of active X genes than males, who only have one copy of the X chromosome. At approximately the time of embryonic implantation, one of the two X chromosomes in each cell of the female embryo is randomly selected for inactivation. Cells then undergo tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skewed X-inactivation
Skewed X-chromosome inactivation (skewed X-inactivation) occurs when the X-inactivation of one X chromosome is favored over the other, leading to an uneven number of cells with each chromosome inactivated. It is usually defined as one allele being found on the active X chromosome in over 75% of cells, and extreme skewing is when over 90% of cells have inactivated the same X chromosome. It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or by secondary nonrandom inactivation, which occurs by selection. X-chromosome inactivation occurs in females to provide dosage compensation between the sexes. If females kept both X chromosomes active, they would have twice the number of active X genes than males, who only have one copy of the X chromosome. At approximately the time of embryonic implantation, one of the two X chromosomes in each cell of the female embryo is randomly selected for inactivation. Cells then undergo tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fragile X Syndrome
Fragile X syndrome (FXS) is a genetic disorder characterized by mild-to-moderate intellectual disability. The average IQ in males with FXS is under 55, while about two thirds of affected females are intellectually disabled. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common, and seizures occur in about 10%. Males are usually more affected than females. This disorder and finding of Fragile X syndrome has an X-linked dominant inheritance. It is typically caused by an expansion of the CGG triplet repeat within the '' FMR1'' (fragile X messenger ribonucleoprotein 1) gene on the X chromosome. This results in silencing ( methylation) of this part of the gene and a deficiency of the resultant protein (FMRP), which is required for the normal development of connections between neurons. D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alport Syndrome
Alport syndrome is a genetic disorder affecting around 1 in 5,000-10,000 children, characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. Alport syndrome can also affect the eyes, though the changes do not usually affect vision, except when changes to the lens occur in later life. Blood in urine is universal. Proteinuria is a feature as kidney disease progresses. The disorder was first identified in a British family by the physician Cecil A. Alport in 1927. Alport syndrome once also had the label hereditary nephritis, but this is misleading as there are many other causes of hereditary kidney disease and 'nephritis'. Alport syndrome is caused by an inherited defect in type IV collagen—a structural material that is needed for the normal function of different parts of the body. Since type IV collagen is found in the ears, eyes, and kidneys, this explains why Alport syndrome affects different seemingly unrelated parts of the body (ears, eyes, kidneys, et ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coffin–Lowry Syndrome
Coffin–Lowry syndrome is a genetic disorder that is X-linked dominant and which causes severe mental problems sometimes associated with abnormalities of growth, cardiac abnormalities, kyphoscoliosis, as well as auditory and visual abnormalities. Presentation Symptoms of disease are more severe in males, who are generally diagnosed in early childhood. Children with CLS display cognitive disabilities of varying severity. Additional neuromuscular features include sleep apnea, muscular spasticity, progressive loss of muscle strength and tone leading to paraplegia or partial paralysis. Affected individuals are at elevated risk of stroke. Some patients experience stimulus-induced drop attacks (SIDAs, temporary paralytic episodes without loss of consciousness), triggered by unpredictable environmental stimuli (touch, scents, sounds, etc.). SIDA episodes become more frequent as the disease progresses, and become frequent around adolescence in males. Additional clinical physical features ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sex Chromosome
A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. Nettie Stevens and Edmund Beecher Wilson both independently discovered sex chromosomes in 1905. However, Stevens is credited for discovering them earlier than Wilson. Differentiation In humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are called autosomes. Autosomes are homologous chromosomes i.e. chromosomes which contain the same genes (regions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dominance And Recessiveness
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and the second recessive. This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new (''de novo'') or inherited. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (autosomes) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child (see Sex linkage). Since there is only one copy of the Y chromosome, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance such as incomplete do ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.svg "Click for more on -> X-linked Recessive")
