Ichthyosis Vulgaris

Ichthyosis vulgaris is an incredibly common (roughly 1/250) condition which is a result of a defect in fillagrin synthesis, and it is autosomal dominant in its inheritance.  For a bonus point, tell me what autosomal dominant means in terms of how diseases are transmitted from parent to child.  It is characterized by large, flat scales on the lower legs, but also in the upper limbs, the back, chest, neck.  The scales predominate in areas that are not well supplied by sweat glands, such as intertriginous areas.  

It is differentiated from eczema craquele by the character of the scale and the location, being much more prominent and wider distributed than eczema craquele.  The picture of lamellar ichthyosis is different, in that the scales, if anything, are accentuated in the flexural areas and they are pretty much universal, as opposed to ichthyosis vulgaris.

If you had to choose an ichthyosis, you should pick ichthyosis vulgaris, because it is more common, hence its name.