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The genetic mechanism behind human skin color is mainly regulated by the enzyme tyrosinase, which creates the color of the skin, eyes, and hair shades. [14] [15] Differences in skin color are also attributed to differences in size and distribution of melanosomes in the skin. [9] Melanocytes produce two types of melanin.
Albinism is a congenital condition characterized in humans by the partial or complete absence of pigment in the skin, hair and eyes. Albinism is associated with a number of vision defects, such as photophobia, nystagmus, and amblyopia. Lack of skin pigmentation makes for more susceptibility to sunburn and skin cancers.
By definition albinism is a genetic condition, however a similar coloration could be caused by diet, living conditions, age, disease, or injury. [ 5 ] Oculocutaneous albinism (OCA) is a clearly defined set of seven types of genetic mutations which reduce or completely prevent the synthesis of eumelanin or pheomelanin , resulting in reduced ...
Gene: Description: OCA1: 203100 606952: TYR: OCA1 is caused by mutations of the tyrosinase gene, and can occur in two variations. The first is OCA1a, and means that the organism cannot synthesize melanin whatsoever. [6] The hair is usually white (often translucent) and the skin is very pale. Vision usually ranges from 20/200 to 20/400.
Darker skin appears to be strongly selected for in equatorial regions to prevent sunburn, skin cancer, the photolysis of folate, and damage to sweat glands. [61] Understanding how genetic diversity in the human population impacts various levels of gene expression is an active area of research.
Autosomal dominant A 50/50 chance of inheritance. Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition. [1]
The skin colour variations are normally distributed from light to dark, as it is usual for polygenic traits. [64] [65] Data collected from studies on MC1R gene has shown that there is a lack of diversity in dark-skinned African samples in the allele of the gene compared to non-African populations. This is remarkable given that the number of ...
Alpine salamanders produce a toxin from their skin, and both fully melanistic, black salamanders and spotted individuals produce the compound. [ 32 ] Studies done that traced DNA histories have suggested that the original alpine salamander phenotype was black with some yellow spots, meaning that the fully black color evolved over time and was ...