Melanism

From ArticleWorld

Melanism or melanosis is a condition of increased numbers of melanocytes or an increased amount of melanin in the skin. In animals, it can involve the hair or feathers as well. Melanin is a dark pigment that exists within cells called melanocytes.

Causes

Most melanism is the result of the entire or nearly entire expression of a dominant gene for dark pigmentation. In other word, it is something an individual or animal is born with. In some animals, a condition called “abundism” involves melanism that exists in patterns such as spots or stripes. If the spots or stripes widen to include most of the body, the condition is known as “pseudo-melanism”.

While melanism is usually a genetic condition, it can occur as a response to the environment. Some animals will change their pattern of melanism to become less able to be seen by predators. In the feline population, some leopards, pumas or jaguars mutate and are called black panthers when the difference between the animals is only pigmentation.

Humans alter their skin melanin as a result of being exposed to the sun. In general, populations that originate near the equator where sun exposure is greatest, have more skin melanin as do populations originating in higher latitudes.

Physiology

The majority of cases of increased melanism (or melanosis) in humans is a result of tanning, although pregnancy and some disease states can cause this. In response to hormones or environmental factors, the melanocytes in the cell produce melanin to reduce the risk of further damage to the tissues. Most of the time, diseases with melanosis are from the same number of melanocytes producing more melanin, although some can involve an increase in the number of melanocytes. Sometimes the body produces melanocytes in the deeper layers of skin (the dermis), which also contributes to the increased pigmentation that can be seen.