Red-Green Colour Blindness
Colour blindness is more accurately known as colour vision deficiency because most sufferers do see some colours but not all colours. Many people believe that all colourblind people see black and white but in reality it is extremely rare for a person to see the world in greyscale. Furthermore, colourblindness affects people differently and there are several types and different levels of impairment. Red-green colour blindness is the general umbrella term for 4 types of colour blindness: protanopia, deuteranopia, protanomaly and deuteranomaly. Those with red-green colour blindness have difficulty discriminating red and green hues because of an absence or mutation of red and/or green photoreceptors in the eyes. It also is one of the most common and most well-known forms of colour blindness.
1. Thorough description of the Type of inheritance
Red-green colour blindness is a X-linked recessive sex-linked trait. X-linked inheritance means that the gene causing the disorder is located on the X-chromosome. Since females have two X-chromosomes and males only have one, gene expression is not the same in both genders. X-linked recessive genes are only expressed in the female if there are two copies of the same gene. Females who only have one copy of the gene will become "carriers" of the gene and can pass it on to their offspring but will not express the trait. However, males only need one copy of the gene for the trait or disorder to be expressed.
1. Thorough description of the Type of inheritance
Red-green colour blindness is a X-linked recessive sex-linked trait. X-linked inheritance means that the gene causing the disorder is located on the X-chromosome. Since females have two X-chromosomes and males only have one, gene expression is not the same in both genders. X-linked recessive genes are only expressed in the female if there are two copies of the same gene. Females who only have one copy of the gene will become "carriers" of the gene and can pass it on to their offspring but will not express the trait. However, males only need one copy of the gene for the trait or disorder to be expressed.
2. Explanation of the chromosome involved and the genetic mutation
The gene for the trait of colour blindness is found only in the X-chromosome which is passed from the mother to the child. Mutations in OPN1LW, OPN1MW, and OPN1SW genes cause the different forms of colour deficiency. Red-green colour blindness is an inherited X-linked recessive gene and OPN1LW and OPN1MW are genes located on the X-chromosome. Genetic changes involving the OPN1LW or OPN1MW genes is what causes red-green vision defects. (http://ghr.nlm.nih.gov/condition/color-vision-deficiency, 2015). These genes affect the cones in the eye. Cones are cells in the retina (light-sensitive tissue lining the back of the eye). Cones detect light and colour and there are three different types of cones that see colour: red, green and blue. Red-green colour blindness occurs when the genetic mutations affect the functioning of the red and green cones, known as "M" and "L" cones. (http://www.ncbi.nlm.nih.gov/books/NBK11059/, 2001).
3. Symptoms/effects of the disease
Some symptoms of colour blindness vary in severity but you may have difficulty distinguishing colours from each other. In red-green colour blindness you will have difficulty telling the difference between red and green shades but will be able to see blue and yellow easily. You may only be able to see a few shades of colours, while most people see thousands of shades. In addition to this, they may have poor vision and an intolerance to bright light.
Although most colourblind people are able to cope with everyday life easily, sometimes the simplest everyday tasks can become inconvenient because of their condition and they have a vastly difference experience with colour compared to "normal" people. For example, depending on the severity, people might not be able to see if they have sunburns, they may not be able to tell if their meat is cooked by the colour, flowers and fruits might become hard to distinguish and coloured maps and graphs can be very hard to decipher. Furthermore, it can be hard to coordinate clothes to wear since you have a limited colour spectrum. In addition to this, colour blind people must be very cautious when driving and make their own system for remembering which signs are what colour and so on. However, the most significant effect of colour blindness could be on a person's career. Colour blind people must take into consideration if their handicap will affect performance, especially if it is a job where good to perfect colour vision is required such as an airline pilot, air traffic controller, police officer, firefighter and train driver.
4. When/how/why the change in genetic material takes place?
For congenital colour blindness, you simply inherit defective genetic material. There is no change that occurs which causes colour blindness. However, red-green colour blindness can also be acquired throughout a person's life. This can be caused by illness, accident or injury, eye complications or medication.
5. How common is the disease?
Red-green colour blindness is one of the most common form of colour vision deficiency and over 99% of colourblind people have red-green colour blindness. About 8% of all men and 0.5% of all women have red-green colour blindness. (http://www.color-blindness.com/, 2015).
6. Does the disease affect some ethnic groups more than others?
Many might expect that colour blindness is the same in different races and ethnic groups. However, based on empirical research around the world, it has been found that Caucasians are more at risk of being born colourblind than any other ethnicity. Australia, The U.K and Britain rank the highest out of 8 countries (Australia, China, Russia, UK, Britain, Mexico, Canada & USA) investigated in the research.
The gene for the trait of colour blindness is found only in the X-chromosome which is passed from the mother to the child. Mutations in OPN1LW, OPN1MW, and OPN1SW genes cause the different forms of colour deficiency. Red-green colour blindness is an inherited X-linked recessive gene and OPN1LW and OPN1MW are genes located on the X-chromosome. Genetic changes involving the OPN1LW or OPN1MW genes is what causes red-green vision defects. (http://ghr.nlm.nih.gov/condition/color-vision-deficiency, 2015). These genes affect the cones in the eye. Cones are cells in the retina (light-sensitive tissue lining the back of the eye). Cones detect light and colour and there are three different types of cones that see colour: red, green and blue. Red-green colour blindness occurs when the genetic mutations affect the functioning of the red and green cones, known as "M" and "L" cones. (http://www.ncbi.nlm.nih.gov/books/NBK11059/, 2001).
3. Symptoms/effects of the disease
Some symptoms of colour blindness vary in severity but you may have difficulty distinguishing colours from each other. In red-green colour blindness you will have difficulty telling the difference between red and green shades but will be able to see blue and yellow easily. You may only be able to see a few shades of colours, while most people see thousands of shades. In addition to this, they may have poor vision and an intolerance to bright light.
Although most colourblind people are able to cope with everyday life easily, sometimes the simplest everyday tasks can become inconvenient because of their condition and they have a vastly difference experience with colour compared to "normal" people. For example, depending on the severity, people might not be able to see if they have sunburns, they may not be able to tell if their meat is cooked by the colour, flowers and fruits might become hard to distinguish and coloured maps and graphs can be very hard to decipher. Furthermore, it can be hard to coordinate clothes to wear since you have a limited colour spectrum. In addition to this, colour blind people must be very cautious when driving and make their own system for remembering which signs are what colour and so on. However, the most significant effect of colour blindness could be on a person's career. Colour blind people must take into consideration if their handicap will affect performance, especially if it is a job where good to perfect colour vision is required such as an airline pilot, air traffic controller, police officer, firefighter and train driver.
4. When/how/why the change in genetic material takes place?
For congenital colour blindness, you simply inherit defective genetic material. There is no change that occurs which causes colour blindness. However, red-green colour blindness can also be acquired throughout a person's life. This can be caused by illness, accident or injury, eye complications or medication.
5. How common is the disease?
Red-green colour blindness is one of the most common form of colour vision deficiency and over 99% of colourblind people have red-green colour blindness. About 8% of all men and 0.5% of all women have red-green colour blindness. (http://www.color-blindness.com/, 2015).
6. Does the disease affect some ethnic groups more than others?
Many might expect that colour blindness is the same in different races and ethnic groups. However, based on empirical research around the world, it has been found that Caucasians are more at risk of being born colourblind than any other ethnicity. Australia, The U.K and Britain rank the highest out of 8 countries (Australia, China, Russia, UK, Britain, Mexico, Canada & USA) investigated in the research.
7. When does the onset of the condition occur and how does the condition progress
Since it is predominantly a congenital disease, red-green colour blindness is present throughout a person's life since birth. Furthermore, the condition doesn't go through any changes; it neither becomes worse or better during a person's life and remains the same. If it is acquired, onset of the condition may be after a person has gone through some trauma, especially in the eye, illness or after a person has taken medication which has colour blindness as a side effect.
8. Treatment/management of the disease
Red-green colour blindness can’t be treated or cured but there are some measures that can be taken to compensate for it. Many colourblind people can live normal everyday lives despite their colour blindness and some have their own system of recognising colours. Furthermore, with today’s technology, specialised glasses with tinted lenses have been made with special filters that can change the way light hits the eye of the colourblind person and make them see colours they once couldn’t.
9. How is the disease diagnosed?
Red-green colour blindness is usually diagnosed in early childhood using simple tests. Tests commonly used to diagnose colour blindness is the Hardy-Rand-Rittler (H-R-R) and the Ishihara Colour Plates. These screening tests are used to evaluate the type and degree of colour deficiency. In the Ishihara Colour Plates test, you are asked to identify numbers, letters or shapes that are in a jumble of dots that vary in colour and size.
10. Preventative measures taken against its inheritance
To prevent a male from being born with colourblindness, the mother should not be a carrier. If the mother is a carrier of the X-chromosome, the male has a 50/50 chance of being colourblind. If the mother is colour blind, then all her sons will be colour blind. Whether or not the father is colour blind doesn't matter because they don't pass their X-chromosome to boys therefore it all depends on the mother's X-chromosomes.
For females, both of their parents need to be carriers of the defective X-chromosome and they must inherit both of the defective chromosomes to become colour blind. If both parents are colour blind, than the female will also be colour blind. But, if only one parent is colour blind, the female might become a carrier of the gene but will not necessarily be colour blind.
Since it is predominantly a congenital disease, red-green colour blindness is present throughout a person's life since birth. Furthermore, the condition doesn't go through any changes; it neither becomes worse or better during a person's life and remains the same. If it is acquired, onset of the condition may be after a person has gone through some trauma, especially in the eye, illness or after a person has taken medication which has colour blindness as a side effect.
8. Treatment/management of the disease
Red-green colour blindness can’t be treated or cured but there are some measures that can be taken to compensate for it. Many colourblind people can live normal everyday lives despite their colour blindness and some have their own system of recognising colours. Furthermore, with today’s technology, specialised glasses with tinted lenses have been made with special filters that can change the way light hits the eye of the colourblind person and make them see colours they once couldn’t.
9. How is the disease diagnosed?
Red-green colour blindness is usually diagnosed in early childhood using simple tests. Tests commonly used to diagnose colour blindness is the Hardy-Rand-Rittler (H-R-R) and the Ishihara Colour Plates. These screening tests are used to evaluate the type and degree of colour deficiency. In the Ishihara Colour Plates test, you are asked to identify numbers, letters or shapes that are in a jumble of dots that vary in colour and size.
10. Preventative measures taken against its inheritance
To prevent a male from being born with colourblindness, the mother should not be a carrier. If the mother is a carrier of the X-chromosome, the male has a 50/50 chance of being colourblind. If the mother is colour blind, then all her sons will be colour blind. Whether or not the father is colour blind doesn't matter because they don't pass their X-chromosome to boys therefore it all depends on the mother's X-chromosomes.
For females, both of their parents need to be carriers of the defective X-chromosome and they must inherit both of the defective chromosomes to become colour blind. If both parents are colour blind, than the female will also be colour blind. But, if only one parent is colour blind, the female might become a carrier of the gene but will not necessarily be colour blind.