After Broca's, observations (1861), it was understood that there are some characteristics in humans such as anatomic, motor, mental and cognitive asymmetries. In this work, mentioned asymmetries have been studied on the twins, including the effect of the hereditary and environmental factors, especially. For this purpose, many previous studies on twins have been looking at, but there was any study about handedness, IQ and the other symmetric, asymmetric features on twins. In this work, studied on twins by handedness (motor), IQ (mental), hemispheric managements (cognitive) and some morphological properties such as head diameter, hands and feet dimensions (anatomic) to determine symmetry-asymmetry features. This study has been done with a subject group of volunteer twins (N=514 people) consist of 148 monozygotic (MZ) and 109 dizigotic (DZ) from every ages but especially primary school students. Monozygotic twins are consisting of 72 female MZ twins and 76 male MZ twins. Dizigotic twins including 59 male-female twins, 29 female DZ twins and 21 male DZ twins. A questionnaire involving Edinburgh Handedness Inventory (EHI) with first ten items and ten questions Yetkin Laterality Questionnaire (YLQ) with second ten items is used to find lateralization degree. The results were assessed by Geshwind scores. For the dominancy of hemispheric management a 35 test including 35 questions is applied. The answers to the questions have a definite point. The points were summed and divided to the number of questions and get a value from 1 to 9. If the result is increasing from 5 to 9, the person has the thinking system of the right hemisphere. If it is decreasing from 5 to 1, the person has the thinking system of the left hemisphere.

The results were compared with lateralization degrees and determined the hemisphere differences and hand preferences in terms of management and IQ. In addition to them, using digital calipers and other measurement devices, the subjects' height in upright position, hand and feet dimensions, head and body length in seating position and determined the body symmetry- asymmetry. According to EHI the average of hand preference was 73, 5% but according to YLQ the value was found 63, 7%. Some twins pair have antagonistic motor, mental, anatomical and cognitive asymmetries which were not a result always expected.

This study has been supported by YYU-Scientific Research Projects 2006-HIS (SBE)-099, Van.