Cohort Effects in a Genetically Determined Trait- Eye Color among US Whites

It was initially believed that blue eye color is inherited in a specific similar pattern as a single recessive trait like that of handedness or hair color. An individual's eye color rarely changes after adulthood hence the cohort differences in the prevalence of the blue eye color in a population would be unanticipated as it's a genetically determined trait. The cohort effects may come as a result of differential survival or may also be as a result of an ancestral distribution of whites in the United States. In addition cohort effects variations reflect a trend in assortative mating. For instance, if two blue-eyed individuals of separate gender marry, they will give birth to blue-eyed children and hence such mating would eventually lead to more number of individuals with blue eyes.

Though there is a slightly different figure between both methods in both more men than women had blue eye color tests for trends in the odds of having blue eye color according to birth year were all highly significant nonetheless The results of the relationship of eye color to reported ancestry in NHANES-I are quite consistent with the geographic concentration of blue eye color among Northern Europeans. When mortality rates according to eye color were analyzed in NHANES-I, it found that there is no meaningful difference in subsequent mortality according to eye color, suggesting that the higher prevalence of blue eye color at old age is not attributable to better survival. Thus it is safe to report that there’s no association between eye color and survival.