Modes of Inheritance of Errors of Refraction

Eighteen families in which both parents had refractions within the range of +4·0 D to −4·0 D and axial lengths seen in emmetropia (22·3-26·0 mm) showed coefficients of correlation of the order 0·5 indicative of polygenic inheritance. Such coefficients were seen for axial length (0·407) and for the cornea (0·487), but not for the lens (which is known to be yoked to the axial length). No such coefficients were seen in 19 families in which one of the parents had axial length outside the emmetropic range (nine families with long axes and 10 with short axes).

The pattern of polygenic inheritance for emmetropia (completely correlated optical components) and errors of refraction up to 4·0 D (inadequately correlated components: correlation ametropia) follows that seen in stature and other measurable characters. In contrast the high refractive errors with their abnormal axial lengths (component ametropia) are—like the extremes in stature—pathological anomalies with monofactorial inheritance.

     

Level of functioning of siblings and parents of probands of varying degrees of retardation

A further analysis of already published data supports the position that retardates of low ability level less frequently have retarded siblings, retarded parents, and parents low in occupational level than do retardates higher in ability level. The analysis supports the position that there are two types of retarded individuals, persons retarded as a result of gene or chromosomal anomalies, brain injury, etc., who more frequently occur in the lower-level retardate group, and persons whose retardation represents polygenic segregation, who more frequently occur in the higher-level group.