Expressivity (genetics)

The number of extra toes can differ between cats, due to variable expressivity of the ZRS gene in the feline chromosome A2.

The syndrome affects connective tissue in the body and has a spectrum of symptoms ranging from mild bone and joint involvement to severe newborn forms and cardiovascular disease.

[16] The gene product is involved in the proper assembly of microfibrils, which are structures found in connective tissues to provide support and elasticity.

[18] Carriers of the rare allele can also have pits near the centre of the lower lip which may appear to be wet due to the presence of salivary glands.

This variation can range so broadly that a study published by the Department of Orthodontics at the University of Athens showed that some individuals were unaware that they possessed the genotype for this condition until they were tested.

[19] Neurofibromatosis (NF1), also known as Von Recklinghausen disease, is a genetic disorder that is caused by a rare mutation in the neurofibromin gene (NF1) on chromosome 17.

Fetal Hemoglobin (HbF) concentration and the presence of alpha-thalassemia, a genetic blood disease in which the alpha globin subunit of the hemoglobin protein is underproduced, are thought to be major contributors to the genetic modification leading to the variable expressivity of hemolysis (destruction of red blood cells) and increasing the severity of the disease.

Figure 1. This figure illustrates some factors influencing gene expressivity including cis-regulatory elements, trans-acting factors, environmental factors, and DNA modification. Credited with Biorender.com.
Figure 3. Example of Cleft lip seen as a result of the Van der Woude syndrome.
Figure 2. Individuals with Marfan Syndrome usually have fingers that are longer than those that do not have the syndrome. The extremity of difference in finger length is a result of variable expressivity.