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Blue Cone Monochromacy
Blue cone monochromacy (BCM) is an inherited eye disease that causes severe color blindness, poor visual acuity, nystagmus, hemeralopia, and photophobia due to the absence of functional red (L) and green (M) cone photoreceptor cells in the retina. BCM is a recessive X-linked disease and almost exclusively affects XY karyotypes. Cause Cone cells are one kind of photoreceptor cell in the retina that are responsible for the photopic visual system and mediate color vision. The cones are categorized according to their spectral sensitivity: * LWS (long wave sensitive) cones are most sensitive to red light. * MWS (middle wave sensitive) cones are most sensitive to green light. * SWS (short wave sensitive) cones are most sensitive to blue light. MWS and LWS cones are most responsible for visual acuity as they are concentrated in the fovea centralis region of the retina, which constitutes the very center of the visual field. Blue cone monochromacy is a severe condition in which the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Acuity
Visual acuity (VA) commonly refers to the clarity of visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye influence the sharpness of an image on its retina. Neural factors include the health and functioning of the retina, of the neural pathways to the brain, and of the interpretative faculty of the brain. The most commonly referred-to visual acuity is ''distance acuity'' or ''far acuity'' (e.g., "20/20 vision"), which describes someone's ability to recognize small details at a far distance. This ability is compromised in people with myopia, also known as short-sightedness or near-sightedness. Another visual acuity is ''Near visual acuity, near acuity'', which describes someone's ability to recognize small details at a near distance. This ability is compromised in people with hyperopia, also known as long-sightedness or far-sightedness. A com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rod Cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~4.6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light. Structure Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the eye. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 120 million rod cells ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photopsin
Vertebrate visual opsins are a subclass of ciliary opsins and mediate vision in vertebrates. They include the opsins in human rod and cone cells. They are often abbreviated to ''opsin'', as they were the first opsins discovered and are still the most widely studied opsins. Opsins Opsin refers strictly to the apoprotein (without bound retinal). When an opsin binds retinal to form a holoprotein, it is referred to as Retinylidene protein. However, the distinction is often ignored, and opsin may refer loosely to both (regardless of whether retinal is bound). Opsins are G-protein-coupled receptors (GPCRs) and must bind retinal — typically 11-''cis''-retinal — in order to be photosensitive, since the retinal acts as the chromophore. When the Retinylidene protein absorbs a photon, the retinal isomerizes and is released by the opsin. The process that follows the isomerization and renewal of retinal is known as the visual cycle. Free 11-''cis''-retinal is photosensitiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OPN1LW
OPN1LW is a gene on the X chromosome that encodes for long wave sensitive (LWS) opsin, or red cone photopigment. The OPN1LW gene provides instructions for making an opsin pigment that is more sensitive to light in the yellow/orange part of the visible spectrum (long-wavelength light). The gene contains 6 exons with variability that induces shifts in the spectral range. OPN1LW is subject to homologous recombination with OPN1MW, as the two have very similar sequences. These recombinations can lead to various vision problems, such as red-green colourblindness and blue monochromacy. The protein encoded is a G-protein coupled receptor with embedded 11-''cis''-retinal, whose light excitation causes a cis-trans conformational change that begins the process of chemical signalling to the brain. It is responsible for perception of visible light in the yellow-green range on the visible spectrum (around 500-570nm). Gene OPN1LW produces red-sensitive opsin, while its counterparts, OPN1MW ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opsin
Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become retinylidene proteins, but are usually still called opsins regardless. Most prominently, they are found in photoreceptor cells of the retina. Five classical groups of opsins are involved in Visual perception, vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the Visual phototransduction, visual transduction cascade. Another opsin found in the mammalian retina, melanopsin, is involved in circadian rhythms and Pupillary light reflex, pupillary reflex but not in vision. Humans have in total nine opsins. Beside vision and light perception, opsins may also sense temperature, sound, or chemicals. Structure and function Animal opsins detect light and are the molecules that allow us to see. Opsins are G-protein-coupled receptors (GPCRs), which are chemoreceptors and hav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Locus Control Region
A locus control region (LCR) is a long-range cis-regulatory element that enhances expression of linked genes at distal chromatin sites. It functions in a copy number-dependent manner and is tissue-specific, as seen in the selective expression of β-globin genes in erythroid cells. Expression levels of genes can be modified by the LCR and gene-proximal elements, such as promoters, enhancers, and silencers. The LCR functions by recruiting chromatin-modifying, coactivator, and transcription complexes. Its sequence is conserved in many vertebrates, and conservation of specific sites may suggest importance in function. It has been compared to a super-enhancer as both perform long-range ''cis'' regulation via recruitment of the transcription complex. History The β-globin LCR was identified over 20 years ago in studies of transgenic mice. These studies determined that the LCR was required for normal regulation of beta-globin gene expression. Evidence of the presence of this add ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. 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 non-coding genes. During gene expression (the synthesis of Gene product, RNA or protein from a gene), DNA is first transcription (biology), copied into RNA. RNA can be non-coding RNA, directly functional or be the intermediate protein biosynthesis, template for the synthesis of a protein. The transmission of genes to an organism's offspring, is the basis of the inheritance of phenotypic traits from one generation to the next. These genes make up different DNA sequences, together called a genotype, that is specific to every given individual, within the gene pool of the population (biology), population of a given species. The genotype, along with environmental and developmental factors, ultimately determines the phenotype ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OMIM
Online Mendelian Inheritance in Man (OMIM) is a continuously updated catalog of human genes and genetic disorders and traits, with a particular focus on the gene-phenotype relationship. , approximately 9,000 of the over 25,000 entries in OMIM represented phenotypes; the rest represented genes, many of which were related to known phenotypes. Versions and history OMIM is the online continuation of Victor A. McKusick's ''Mendelian Inheritance in Man'' (MIM), which was published in 12 editions between 1966 and 1998.McKusick, V. A. ''Mendelian Inheritance in Man. Catalogs of Autosomal Dominant, Autosomal Recessive and X-Linked Phenotypes.'' Baltimore, MD: Johns Hopkins University Press, 1st ed, 1996; 2nd ed, 1969; 3rd ed, 1971; 4th ed, 1975; 5th ed, 1978; 6th ed, 1983; 7th ed, 1986; 8th ed, 1988; 9th ed, 1990; 10th ed, 1992. Nearly all of the 1,486 entries in the first edition of MIM discussed phenotypes. MIM/OMIM is produced and curated at the Johns Hopkins School of Medicine ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Locus (genetics)
In genetics, a locus (: loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of Human genome#Coding sequences (protein-coding genes), protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000. Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus. Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygote, homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygote, heterozygous. The ordered list of loci known for a particular genome is called a gene map. Gene mapping is the process of determining the specific locus or loci responsible for producing a particular phenotype or biological trait. Association ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene Cluster
A gene cluster is a group of two or more genes found within an organism's DNA that encode similar peptide, polypeptides or proteins which collectively share a generalized function and are often located within a few thousand base pairs of each other. The size of gene clusters can vary significantly, from a few genes to several hundred genes. Portions of the DNA sequence of each gene within a gene cluster are found to be identical; however, the protein encoded by each gene is distinct from the proteins encoded by the other genes within the cluster. Gene clusters often result from expansions of a single gene caused by repeated duplication events, and may be observed near one another on the same chromosome or on different, but homologous chromosomes. An example of a gene cluster is the Hox gene, which is made up of eight genes and is part of the Homeobox gene family. Formation Historically, four models have been proposed for the formation and persistence of gene clusters. Gene dupli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dichromacy
Dichromacy (from Greek ''di'', meaning "two" and ''chromo'', meaning "color") is the state of having two types of functioning photoreceptors, called cone cells, in the eyes. Organisms with dichromacy are called dichromats. Dichromats require only two primary colors to be able to represent their visible gamut. By comparison, trichromats need three primary colors, and tetrachromats need four. Likewise, every color in a dichromat's gamut can be evoked monochromatic light. By comparison, every color in a trichromat's gamut can be evoked with a combination of monochromatic light and white light. Dichromacy in humans is a color vision deficiency in which one of the three cone cells is absent or not functioning and color is thereby reduced to two dimensions. Perception Dichromatic color vision is enabled by two types of cone cells with different spectral sensitivities and the neural framework to compare the excitation of the different cone cells. The resulting color vision ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesopic Vision
Mesopic vision, sometimes also called twilight vision, is a combination of photopic and scotopic vision under low-light (but not necessarily dark) conditions. Mesopic levels range approximately from 0.01 to 3.0 cd/m2 in luminance. Most nighttime outdoor and street lighting conditions are in the mesopic range. Human eyes respond to certain light levels differently. This is because under high light levels typical during daytime (photopic vision), the eye uses cones to process light. Under very low light levels, corresponding to moonless nights without artificial lighting (scotopic vision), the eye uses rods to process light. At many nighttime levels, a combination of both cones and rods supports vision. Photopic vision facilitates excellent color perception, whereas colors are barely perceptible under scotopic vision. Mesopic vision falls between these two extremes. In most nighttime environments, enough ambient light prevents true scotopic vision. In the words of Duco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
