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Once an X is inactivated, it remains inactivated throughout the life of that cell and any of its daughter cells. X-inactivation is reversed in female germline cells, so that all new oocytes receive an active X. Regardless of which X is inactivated in her somatic cells, a female will have a 50% chance of passing on the disease to any male children.
Ichthyosis (also named fish scale disease) [1] is a family of genetic skin disorders characterized by dry, thickened, scaly skin. [2] The more than 20 types of ichthyosis range in severity of symptoms, outward appearance, underlying genetic cause and mode of inheritance (e.g., dominant, recessive, autosomal or X-linked). [3]
Cell replacement: In some parts of the body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. [58] New cells are formed by mitosis and so are exact copies of the cells being replaced. In like manner, red blood cells have a short lifespan (only about 3 months) and new RBCs are formed by mitosis. [59]
In rare cases, intersex conditions can be caused by mosaicism where some cells in the body have XX and others XY chromosomes . [ 15 ] [ 16 ] In the fruit fly Drosophila melanogaster , where a fly possessing two X chromosomes is a female and a fly possessing a single X chromosome is a sterile male, a loss of an X chromosome early in embryonic ...
In eukaryotes, there are two distinct types of cell division: a vegetative division , producing daughter cells genetically identical to the parent cell, and a cell division that produces haploid gametes for sexual reproduction , reducing the number of chromosomes from two of each type in the diploid parent cell to one of each type in the ...
The skin weighs an average of 4 kg (8.8 lb), covers an area of about 2 m 2 (22 sq ft), and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. [1] The two main types of human skin are glabrous skin, the nonhairy skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. [16]
Others serve to anchor the epidermis glabrous skin (hairless), and hyper-proliferative epidermis (from a skin disease). [1] They divide to form the keratinocytes of the stratum spinosum, which migrate superficially. [2] Other types of cells found within the stratum basale are melanocytes (pigment-producing cells) and Merkel cells (touch receptors).
Scale forms on the skin surface in various disease settings, and is the result of abnormal desquamation. In pathologic desquamation, such as that seen in X-linked ichthyosis, the stratum corneum becomes thicker (hyperkeratosis), imparting a "dry" or scaly appearance to the skin, and instead of detaching as single cells, corneocytes are shed in clusters, which forms visible scales. [2]