AP PSYCHOLOGY

Detailed explanation-1: -Monozygotic (MZ) twins arise from a single zygote, and have always been thought to inherit identical genomic sequences [1], whereas dizygotic (DZ) twins arise from two different zygotes and, just like siblings, share on average 50% identity in their genomic sequence.

Detailed explanation-2: -Monozygotic and dizygotic twin concordances are approximately 85% and 50%, respectively, for reading, and 70% and 50% for mathematics.

Detailed explanation-3: -The pair-wise concordance rates in schizophrenia are 30–40% in MZ and 5–10% in DZ, with somewhat higher rates for proband concordance. The findings from twin studies support the diathesis stress model in schizophrenia, and it is argued that the polygenic model gives the best explanation for the empirical findings.

Detailed explanation-4: -Since MZ twins are genetically identical, as compared with DZ twins who only share, on average, half of their genomes, a greater concordance rate, that is, a greater phenotypic similarity, in MZ twins than in DZ twins is likely due to greater genetic similarity.