PSYC 100A Chapter Notes - Chapter 4: Twin, Prenatal Development, Active Child

• School: University of Victoria
• Department: Psychology
• Course: PSYC 100A
• Professor: Martin Sherer Smith

Document Summary

Fraternal twins (monozygotic) develop a single fertilized egg that splits in two. Thus they are genetically identical: although identical twins have the same genes, they do not always have the same number of copies of those genes. That variation helps explain why one twin may have a greater risk for a certain illness: most identical twins share a placenta during prenatal development, but one of every three sets have separate placentas. Fraternal twins (dizygotic) develop from two separate fertilized eggs. As womb-mates, they share a prenatal environment, but they are genetically no more similar than ordinary brothers and sisters. Temperament is a person"s characteristic emotional reactivity and intensity. The most emotionally reactive new borns tended also to be the most reactive 9-month- olds. Shy 6-month-olds tended to still be shy as 13-year-olds. Identical twins, more than fraternal twins, often have similar temperaments.