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Eye development is initiated by the master control gene PAX6, a homeobox gene with known homologues in humans (aniridia), mice (small eye), and Drosophila (eyeless). The PAX6 gene locus is a transcription factor for the various genes and growth factors involved in eye formation.
As of 2010, as many as 16 genes have been associated with eye color inheritance. Some of the eye-color genes include OCA2 and HERC2. [9] [10] The earlier belief that blue eye color is a recessive trait has been shown to be incorrect, and the genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.
The third gene array shows a deuteranopia genotype; the fourth shows a normal color vision genotype. When unequal recombination happens with breaks between the genes (depicted by blue lines), a gene can be essentially deleted from one of the chromosomes. This gene deletion leads to protanopia or deuteranopia (congenital red–green dichromacy).
Pleiotropy can have an effect on the evolutionary rate of genes and allele frequencies. Traditionally, models of pleiotropy have predicted that evolutionary rate of genes is related negatively with pleiotropy – as the number of traits of an organism increases, the evolutionary rates of genes in the organism's population decrease. [10]
Retinitis pigmentosa (RP) is a member of a group of genetic disorders called inherited retinal dystrophy (IRD) that cause loss of vision. [1] Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). [1]
Rhodopsin, also known as visual purple, is a protein encoded by the RHO gene [5] and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. [6]
Familial exudative vitreoretinopathy (FEVR, pronounced as fever) is a genetic disorder affecting the growth and development of blood vessels in the retina of the eye. This disease can lead to visual impairment and sometimes complete blindness in one or both eyes. FEVR is characterized by incomplete vascularization of the peripheral retina.
The most common form is caused by a genetic condition called congenital red–green color blindness (including protan and deutan types), which affects up to 1 in 12 males (8%) and 1 in 200 females (0.5%). [3] The condition is more prevalent in males, because the opsin genes responsible are located on the X chromosome. [2]