A Twin Study of Genetic Influences in Reoding Achievement

Abstract

The California Reading Achievement Test was administered to 70 pairs of same-sex twins, ages 9 to 12 years. Intraclass (within-pair) correlations were significantly higher for monozygotic (MZ) than for dizygotic (DZ) pairs, and F ratios of variance showed that the DZ pairs had significantly greater within-pair variability than the MZ pairs. The results were in close agreement with findings of previous studies, and together are indicative of hereditary influences in reading achievement. The MZ twins' reading scores were found in a bimodal rather than a normal distribution, suggesting a recessive gene influence on relatively lower reading scores. Tentative support for this suggestion was found by comparing the observed distribution with that expected from a recessive gene model. The advantages are discussed for utilizing twin samples for further research into (1) inherited underlying traits which might influence reading achievement, and (2) environmental contributions to reading achievement.

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