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If the parents are both right-handed, in dizygotic and monozygotic twins there is a 21% chance of one being left-handed. If one parent is left-handed, in DZ and MZ twins there is a 57% chance of one being left-handed. If both parents are left-handed, it is almost certain one twin will be left-handed. [citation needed]
The Twins Early Development Study (TEDS) is an ongoing longitudinal twin study based at King's College London. The main goal of TEDS is to use behavioural genetic methods to find out how nature ( genes ) and nurture (environments) can explain why people differ with respect to their cognitive abilities, learning abilities and behaviours.
The power of twin designs arises from the fact that twins may be either identical (monozygotic (MZ), i.e. developing from a single fertilized egg and therefore sharing all of their polymorphic alleles) or fraternal (dizygotic (DZ), i.e. developing from two fertilized eggs and therefore sharing on average 50% of their alleles, the same level of genetic similarity found in non-twin siblings).
Handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed. [23] A large study of twins from 25,732 families by Medland et al. (2006) indicates that the heritability of handedness is roughly 24%. [24]
Thomas J. Bouchard Jr. (born October 3, 1937) is an American psychologist known for his behavioral genetics studies of twins raised apart. He is professor emeritus of psychology and director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota.
Nancy L. Segal was born a twin in Boston, Massachusetts, in 1951.She received a B.A. from Boston University (psychology, with honors and English literature, double major, 1973), a M.A. from the University of Chicago (Division of Social Sciences, 1974), and was awarded a Ph.D. from the University of Chicago (Committee on Human Development, 1982).
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Gesell created the term "reciprocal interweaving" to describe the developmental process in which two opposite tendencies gradually reach an effective balance. For example, when a child is developing a preference for “handedness”, he or she uses first one hand and then the other, and eventually ends up with a preferred pattern of hand use. [10]