Where does skin color come from ?
Sunday, June 17, 2007
SOURCE: biology-online.org
Skin color is an excellent example of genetic control at work. Skin color depends on the degree of melanin found in skin cells. The amount of melanin is pre-determined by the genetic blueprint of some genes in each cell. To be exact, there are two genes that control the production of melanin, each of which has a dominant and recessive expression. This leads to a possible 16 combinations of genotype when coding for skin color, as seen below.
Although there are 16 possible combinations in expressing the skin phenotype, there are 5 different possible genotypes that the genes of melanin can express for, as indicated above. Each expression of melanin has an accumulating effect on skin tone, until maximum expression of melanin through 4 dominant alleles leads to a black skin phenotype.
Therefore, when any person is born, they will be one of five colours. After this, external factors such as UV sunlight from the sun will change the skin colour away from the genetic expression of its initial colour.
Eye Colour
Melanin is also present in the iris of the eye, therefore its accumulating effect on colour determines the colour of the eye depending on how many dominant and recessive alleles are expressed. The coding for brown eyes is dominant to the coding of blue eyes.
Albinism
Albinism is an occurrence caused by a deficiency of a particular enzyme in a biochemical pathway. The resultant effect is that no melanin is present in the organism, which show pale eyes and white hair/skin. This is not a lethal occurrence in organisms, provided they are not over exposed to ultraviolet radiation from the sun, which can be carcinogenic.
More information about the way genes control and determine the make up of our body is investigated upon on the next page.
Skin color is an excellent example of genetic control at work. Skin color depends on the degree of melanin found in skin cells. The amount of melanin is pre-determined by the genetic blueprint of some genes in each cell. To be exact, there are two genes that control the production of melanin, each of which has a dominant and recessive expression. This leads to a possible 16 combinations of genotype when coding for skin color, as seen below.
 | Key # Genotype 1 M1M1M2M2 2 M1M1M2m2 3 M1M1m2m2 4 M1m1m2m2 5 m1m1m2m2 | Phenotype Black Skin Dark Brown Skin Brown Skin Light Brown Skin White Skin |
Although there are 16 possible combinations in expressing the skin phenotype, there are 5 different possible genotypes that the genes of melanin can express for, as indicated above. Each expression of melanin has an accumulating effect on skin tone, until maximum expression of melanin through 4 dominant alleles leads to a black skin phenotype.
Therefore, when any person is born, they will be one of five colours. After this, external factors such as UV sunlight from the sun will change the skin colour away from the genetic expression of its initial colour.
Eye Colour
Melanin is also present in the iris of the eye, therefore its accumulating effect on colour determines the colour of the eye depending on how many dominant and recessive alleles are expressed. The coding for brown eyes is dominant to the coding of blue eyes.
Albinism
Albinism is an occurrence caused by a deficiency of a particular enzyme in a biochemical pathway. The resultant effect is that no melanin is present in the organism, which show pale eyes and white hair/skin. This is not a lethal occurrence in organisms, provided they are not over exposed to ultraviolet radiation from the sun, which can be carcinogenic.
More information about the way genes control and determine the make up of our body is investigated upon on the next page.
