The etiology of individual differences in literacy, phonological awareness, and language ability is reported in 126 pairs of monozygotic and dizygotic twins. At age 6 and 7 years, more than 60% of the variance in literacy was heritable. Heritabilities for 6- and 7-year-olds were .52 and .62, respectively, for phonological awareness and .43 and .50, respectively, for language ability. After genetic effects on IQ were controlled, a separate genetic influence was identified that acted on literacy, phonological awareness, and language. No genetic link between phonological awareness and literacy independent of general language ability was found; such covariance was mediated through environmental influences. Individual differences in literacy ability are substantially influenced by genetic factors, some of which also act on phonological awareness and general language ability.
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Hohnen et al. (1999) studied this question.
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