A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotection in animal cells and tissues.
Melanosomes are synthesised in the skin in melanocyte cells, as well as the eye in choroidal melanocytes and retinal pigment epithelial (RPE) cells. In lower vertebrates, they are found in melanophores or chromatophores.
The little penguin (Eudyptula minor) is the smallest species of penguin in the world, and originates from New Zealand. It is commonly known as the fairy penguin, little blue penguin, or blue penguin, owing to its slate-blue plumage and is also known by its Māori name kororā. It is a marine neritic species that dives for food throughout the day and returns to burrows on the shore at dusk. Eudyptula minor feathers are dense in melanosomes, which increase water resistance and give them their unique blue colour.
The Australian little penguin (Eudyptula novaehollandiae), from Australia and the Otago region of New Zealand, was initially described as Spheniscus novaehollandiae in 1826 and was later classified as Eudyptula minor novaehollandiae, a subspecies of the little penguin.
Light skin is a human skin color that has a low level of eumelanin pigmentation as an adaptation to environments of low UV radiation.Due to migrations of people in recent centuries, light-skinned populations today are found all over the world. Light skin is most commonly found amongst the native populations of Europe, East Asia, West Asia, Central Asia, South Asia, Siberia, and North Africa as measured through skin reflectance. People with light skin pigmentation are often referred to as "white", but the majority of countries officially categorize people by ethnic or national origin and not by perceived skin tone. Furthermore, definitions and perceptions of "ethnicity" or "race" vary greatly from country to country.
Humans with light skin pigmentation have skin with low amounts of eumelanin, and possess fewer melanosomes than humans with dark skin pigmentation. Light skin provides better absorption qualities of ultraviolet radiation, which helps the body to synthesize higher amounts of vitamin D for bodily processes such as calcium development. On the other hand, light-skinned people who live near the equator, where there is abundant sunlight, are at an increased risk of folate depletion. As a consequence of folate depletion, they are at a higher risk of DNA damage, birth defects, and numerous types of cancers, especially skin cancer. Humans with darker skin who live further from the tropics may have lower vitamin D levels, which can also lead to health complications, both physical and mental, including miscarriage and a greater risk of developing schizophrenia. These two observations form the "vitamin D–folate hypothesis", which attempts to explain why populations that migrated away from the tropics into areas of low UV radiation evolved to have light skin pigmentation.
Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart found in many mammals and birds. Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby keratinocytes to induce pigmentation. Thus darker skin tones have more melanosomes present than lighter skin tones. Functionally, melanin serves as protection against UV radiation. Melanocytes also have a role in the immune system.
The iris pigment epithelium (IPE) is a one cell thick layer of cuboidal cells lying behind the iris. The epithelial cells are highly pigmented due to the numerous large melanosomes which pack the cytoplasm of each cell. Towards the central axis, the IPE terminates at the pupillary margin. Peripherally, the IPE is continuous with the inner, non-pigmented layer of the ciliary epithelium. The iris dilator muscle is strictly attached to the anterior side of the iris pigmented epithelium and represents the anterior continuation of the pigmented ciliary epithelium. The ciliary epithelia represent the anterior continuation of the multilayered retina, whose retinal pigmented epithelium (RPE) corresponds to the pigmented ciliary epithelium, while the multilayered sensory retina fades into the non-pigmented ciliary epithelium. Despite their very different functions and histological appearances, these regions have a common origin from the two layers of the embryological optic cup. The melanosomes of the IPE are distinctive, being larger, blacker and rounder than those in the ciliary epithelium or RPE.