Colour Blindness

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by sydkazz
Last updated 8 years ago

Health & Fitness

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Colour Blindness

GENETIC DISORDERSA genetic disorder is a disease resulting from an abnormality or mutation in a person’s DNA. DNA is received from an offspring’s parents. This DNA must make an exact replication of itself in order to be able to pass it on to its offspring. Sometimes, this replication isn’t a perfect copy and contains a slight difference from the original DNA sequence coding. That difference or mistake during replication is a mutation, and often results from a problem with the DNA bases. On some occasions, bases are simply paired incorrectly; other times extra bases are inserted or missing from the DNA sequence. Normally, base sequences work to develop proteins that enable the body to work and grow. Improper base sequencing often results in non-functioning proteins, resulting in abnormalities. Some abnormalities are small and minor, and found in only a single gene, while others are the effect of an additional or missing chromosome or chromosome pair.

INTRO TO GENETIC DISORDERS:DNAEvery cell in a living organism is composed of DNA. DNA is an organism’s coding for who they are and how they work; it’s their genetic programing that tells and enables their cells to function properly and is the reason for why they are the way they are. It is ultimately our genetic information, found in DNA that carries the information on how to build and maintain an organism; it’s the reason things behave and look as they do. Everyone’s genetic information is sequenced and coded specifically to ensure this. DNA is composed of four chemical bases. Each base pairs with another, forming a sequence. These base pair sequences are an organism’s coding that functions to determine and create them. Within every cell, DNA is organized into chromosomes. Chromosomes are basically bundled up DNA. For organisms that reproduce sexually, chromosomes come in pairs: humans, for example, have 32 pairs. One of each pair of chromosomes is maternal (mother) and the other is paternal (father). So, for these organisms, each of their traits comes from a combination of genes from both the mother and father. Genes are segments of DNA carried on chromosomes and are responsible for controlling hereditary characteristics - they determine specific human traits.


COLOUR BLINDNESS CONTROVERSIESThere are few controversies over colour blindness. The only fairly prominent one is the debate over whether or not schools should alter their teaching methods for young grades. Many lessons are colour based and oriented, and disregard the children that are colour blind. This has led to learning complications and confusion in the past. Many think schools should introduce colour blind testing at an early age and that the programs should be altered so as not to base or greatly relate learning to colour. Others agree with the current teaching methods and think that learning with colour gives children advantages and works to help them.

SYMPTOMS OF COLOUR BLINDNESSThe symptoms of colour blindness are related to the different types of colour blindness and its severity: • Some colours may be seen, but not others (people might not be able to differentiate between red and green, but can see blue and yellow).• Many colors might be seen, so people may not know that they see color differently from other people.• Only a few shades or depths of color might be seen, whereas most people can see thousands of colors and their shades/depths.•In rare and extreme cases, people may see only black, white, and gray.

HISTORY OF COLOUR BLINDNESSThe first theory relating to colour blindness was developed by a colour blind John Dalton in 1793 when he wrote a scientific paper entitled “Extraordinary facts relating to the vision of colours.” He developed a theory stating that colour blindness was caused by a coloured liquid inside the eyeball, and that it was the source for different colour perception. His theory was later disproved when his eyes were examined after his death, and this liquid could not be found. Thomas Young and Hermann von Helmholtz developed the next theory of trichromatic vision. They proposed that colour vision is the result of three different light receptors, and therefore people with normal colour vision require three wavelengths of light to create different colours. Helmholtz used colour-matching experiments in which people would alter amounts of three wavelengths of light to match a test colour. No colour could be matched with just two wavelengths, but any colour on the spectrum could be reached with three. The theory became known as the Young-Helmholtz theory of color vision. The identification of the three receptors however, didn’t come until almost 70 years later. Researchers discovered that cones have different levels of absorption due to their amounts of acids. The different cone receptors are:• Short-wavelength cone receptors• Middle-wavelength cone receptors• Long-wavelength cone receptors

HEREDITARY Certain human characteristics are the result of a single gene from either the mother or father, or a gene combination from both the mother and father. When two different genes combine to form the same characteristic, one of them takes over and is the resulting visible trait. This gene is known as the dominant gene. The other gene is still present but not clearly visible and is referred to as the recessive trait. Dominant traits will take over as long as they are present within an organism. The only time where a recessive trait is visible is when only recessive genes have been inherited for a specific characteristic. When abnormalities, or gene mutations exists in an egg or sperm cell, children can inherit the mutated gene from their parents. Because people inherit a gene from each parent, having one disease gene most likely won’t cause problems because the normal gene will allow the body to make its required, normal protein. Problems occur when the dominant gene carries the mutation or when the same recessive disease gene is inherited from both parents. If a person carries the dominant gene for a disease, their child has a 50 percent chance of inheriting that gene. They receive only one of two genes and as long as the dominant gene is inherited, it will take over. When two carriers of a recessive disease gene have a child, they have a 25 percent chance of inheriting the diseased gene, because they must inherit said gene from both parents. This person still has a 50 percent chance of being a carrier of the mutated gene, and a 25 percent chance they will not inherit the diseased gene at all.

COLOUR BLINDNESS CAUSE AND INHERITANCEIf a person is colour-blind, it’s a result from improper instruction for the development of cone cells. Cells may be missing, or too sensitive, or the pathway from the cone cells to the brain could be improperly developed. Cones are photoreceptor cells in the retina or back of the eye that are responsible for registering colour and detail. Ultimately, they’re colour sensing cells of the eye. They receive light and pass the resulting coloured images to the brain. There are three kinds of cones in the human eye: red, green, and blue. Each receives and responds to variation in colour in different ways; each is sensitive to a certain wavelength of light (red, green, blue). The colours that we see therefore result from the combination of cones perceiving and reacting to certain wavelengths of light. People who suffer from colour blindness have mutations in their genes that causes them to lose or have displaced cones. When the cones aren’t properly aligned, they don’t perceive and react to wavelengths of light as they should. Their perception is therefore restricted to a narrower colour spectrum, and it is difficult to differentiate between colours and their variations. People may not be able to see a colour at all, or they see a different shade or different colour entirely. This is colour blindness. The severity of the colour blindness is dependent upon how out of place the receptive peaks of the cones are.Colour blindness is inherited through receiving a genetically mutated gene on the sex chromosome, X. Males have an X and a Y, versus females who have both X. This is why colour blindness is more common in men than in women. Males need only to receive one genetically mutated X to be colour blind, but females must inherit two mutated X’s. If they receive just one defective gene, the normal one will protect the female from being colour blind. They may still be carriers of the defective gene and are thus still able to pass colorblindness on to their children, however.

This image is of colours that the normal person sees

TYPES OF COLOUR BLINDNESSThere are varying types of colourblindess:• Monochromatism: Cones are lost or non-functional, or just one type of cone is present and functional. • Dichromatism: Only two different cone types are present and the other is missing completely.• Anomalous Trichromatism: All three types of cones are present but one has shifted and therefore is not as sensitive or receptive. This results in a smaller colour spectrum. Dischromats and anomalous trichromats vary in their types as well, according to their missing or malfunctioning cone:• Tritanopia/Tritanomaly: The short-wavelength cone receptor that perceives blue colour, depth, and shade is missing or malfunctioning.• Deuteranomaly: The medium-wavelength cone receptor that perceives green colour, depth, and shade is missing or malfunctioning. A deuteranomalous person is considered green-weak. • The red, orange, yellow, and green region of the spectrum appears somewhat shifted towards red, and each colour is therefore hard to differentiate between. Deuteranomalous individuals don’t, however, have trouble sensing or distinguishing between brightness.• Dichromasy/Deuteranopia: Red, orange, yellow, green, and their varying shades all appear as the same colour and with perceptible differences. • Protanomaly: The long-wavelength cone receptor that perceives red colour, depth, and shade is missing or malfunctioning. This is referred to as red-weakness .The saturation, depth, and brightness of red are seen more weakly by a protanomalous viewer that the normal viewer. • Red, orange, yellow, and yellow-green all appear paler and more green than to the normal observer. Purple also appears blue to a protanomalous viewer, as purple is a combination of red and blue colour. The observer in unable to detect the red in the purple, and so it appears only blue. • Protanopia: The brightness of red, orange, and yellow is very much reduced, sometimes so much so that reds are confused with black or dark gray. Purple and its shades appear blue because their red components are so dimmed.

Top left: normal colour visionTop right: protanopiaBottom left: deuteranopiaBottom right: tritanopia

COLOUR BLINDNESS TREATMENTS Inherited colour blindness cannot be cured, but there are things that colour blind people can do to help themselves:• Wearing colored contact lenses might help people see differences between colors. They don't provide normal color vision, however, and can distort objects.• Wearing glasses that block glare can help to differentiate between colors. Colour blind people see better when there is less glare and brightness.• Learning to look for clues/signs/cues like brightness or location, rather than colors will make things easier. (Ex: learning the order of traffic light colours versus the actual colours).• Proper eye care will prevent from further future damage. Colour Blindness can be corrected to an extent, however:• Developments in light filtering lenses have actually given colour blind people a greater ability to differentiate between certain colour shades that would normally look the same to them.

GENE THERAPYScientists are aware that curing colorblindness requires a form of gene therapy. Doing this would repair the damaged and mutated chromosome/gene/section of DNA that is the reason for the colour blindness mutation. There currently isn’t however, a scientific method developed or available to preform gene therapy correctly on humans to cure colour blindness. Gene therapy is the replacement of dysfunctional, mutated genes with healthy, fully functional ones. It’s an experimental technique that uses genes to treat or prevent diseases. Scientists have discovered how to remove a mutated gene and insert a normal, proper one into the same position so as to have it correctly functioning. This has worked to treat and cure hereditary diseases and cancers in the past. It’s a difficult process, however, due to the problems with carrying large sections of DNA.Gene therapy has been tested to restore colour vision on previously colour blind squirrel monkeys. Both were unable to distinguish between red and green colour and their variations. The therapy actually worked for both, who are now fully able to see all colours of the spectrum. This gives people hope that a similar cure/treatment for colour blindness in humans will be developed and usable shortly.

Each of the three cones is sensitive to a specific wavelength. Short-wavelength cone receptors are sensitive to short wavelength light (blue), middle-wavelength cone receptors are sensitive to medium wavelength light (green), and long-wavelength cone receptors are sensitive to long wavelength light (red). This image shows that.

This image is a diagram of the human eye.

To the right is a brief video describing scientists' use of gene therapy to cure colourblindness and its effects on squirrel monkeys.

This image is of a colourblindness test. If the numbers cannot be seen or distinguished, the person is colourblind.


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