abetalipoproteinemia or (Brit.) abetalipoproteinaemia an autosomal recessive disorder in which plasma lipoproteins lack apolipoprotein B. There is defective assembly and secretion both of chylomicrons in intestinal mucosa and of very-low-density lipoproteins in the liver. The cause is a deficiency of the 88 kDa subunit of microsomal triglyceride transfer protein.

ABC transporter a membrane transport protein having the ABC molecular domain, named after ATP-binding cassette, characteristic of all members of a large superfamily of membrane transport proteins that hydrolyse ATP and transfer a diverse array of small molecules across membranes.

ABC model a model for specification of floral organs especially in Arabidopsis thaliana. It views the floral primordium as comprising four whorls whose developmental fate is determined by the concentric and combinatorial activity of three classes of gene, denoted A, B, and C, which encode transcription factors. Class A determines the fate of whorls 1