Melanoblast cells appear in basal layer of epidermis during-
**Core Concept**
Melanoblasts are the precursor cells of melanocytes, which are responsible for producing melanin, the pigment responsible for skin color. The migration and differentiation of melanoblasts into melanocytes is a crucial process in skin development and pigmentation.
**Why the Correct Answer is Right**
During embryonic development, melanoblasts originate from the neural crest and migrate to the epidermis, where they eventually settle in the basal layer. This is a critical step in the formation of the skin's pigmentary system. The basal layer is the layer of the epidermis where cell division and differentiation occur, making it an ideal location for melanoblasts to mature into functional melanocytes.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as melanoblasts do not appear in the stratum corneum, which is the outermost layer of the epidermis and is composed of dead, flattened cells.
**Option B:** Incorrect, as melanoblasts are not found in the dermis, which is the layer of skin beneath the epidermis.
**Option C:** Incorrect, as melanoblasts do not appear in the sebaceous glands, which are responsible for producing sebum, an oily substance that helps to lubricate the skin.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that melanoblasts migrate to the epidermis during embryonic development, and their presence in the basal layer is critical for the formation of melanocytes and skin pigmentation. This process is essential for the development of normal skin color and function.
**Correct Answer: C. 18-20 weeks of gestation**