A dominant gene will always be expressed when present, such as in the homozygous dominant genotype (RR), or heterozygous genotype (Rr). A recessive allele is only expressed wh â¦ en the genotype is homozygous recessive (rr).
(Lung alveoli, in contrast, are lined by very thin simple squamous epithelium .). Pseudostratified respiratory epithelium consists primarily of columnar ciliated cells. Ciliary beating sweeps mucus and the dust it carries up the bronchi and trachea toward the pharynx, where it can be swallowed.
Four layers of tissues make up the walls of the trachea: 1  The mucosa is the innermost layer and consists of ciliated pseudostratified columnar epithelium with many goblet cells. 2  Deep to the mucosa is the submucosa layer, which is made of areolar connective tissue containing blood vessels and nervous tissue.