Hundreds or thousands of genes are packed into chromosomes. Normal females have 22 pairs of autosomes and two X sex chromosomes. Normal males have 22 pairs of autosomes, one X chromosome and one Y chromosome. The two counterpart genes are called alleles. Congenital anomalies, such as cleft lip with or without cleft palate, may result from genetic factors, environmental factors, or a combination.
Chromosome disorders involve abnormalities in the number or structure of chromosomes.
Single gene conditions are also referred to as monogenic conditions. These are classified as either autosomal dominant, autosomal recessive, and X-linked. There are approximately 350 syndromes that involve orofacial clefting.