Effects of heterosis on growth in height and its segments: a cross-sectional study of the Khasi girls in Northeast India

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Abstract
Background: It is generally believed that improvement in environmental quality is the main factor responsible for the better growth and nutritional status of children in developing countries. However, it is still not clear whether this better growth performance is also associated with heterosis and/or gene flow that may take place as a result of the geographical movement of individuals, or migration. Aim: The present paper attempts to examine the effects of heterosis on physical growth of girls in height and its segments. Subjects and methods: A cross-sectional sample of the Khasi girls of Shillong in Northeast India was considered in the present analysis. The height and sitting height of 1368 girls aged 3-18 years were measured with a Harpenden anthropometer, following standard techniques. The sample was divided into two groups, namely hybrid (HB) and non-hybrid (NHB) girls, in order to test the effects of heterosis using analysis of covariance with the household income as a covariate. The Preece-Baines model 1 (M. A. Preece and M. F. Baines, Annals of Human Biology, 5, 1-24, 1978) was used to fit the adjusted means of height and its segments with a view to assess the variation in adult height, age at peak velocity and size at peak velocity. Results: Both HB and NHB girls were similar in age at maximum increment for height (12 years) and sitting height (13 years), although it was much earlier in the former (10.5 years) than in the latter (11.9 years) with respect to subischial length. The results indicated that HB girls were larger than NHB girls across ages. Such a higher anthropometric status in HB girls was mainly due to their higher growth velocities before the adolescent period. The effect of heterosis after household income was highly significant at many ages from 6 to 18 years, although it was not clearly perceptible in the case of subischial length. Conclusion: Subject to further studies, the role of heterosis and/or gene flow in influencing growth and development of children cannot be completely ruled out, especially after 5 years of age when the variation in growth patterns is likely to be associated not only with environmental quality but also with genetic mechanisms.