Final answer:
Peripheral blood is the most suitable specimen for cytogenetic analysis as it contains white blood cells that can be stimulated to divide, a necessary step in karyotyping.
Step-by-step explanation:
The most suitable specimen for cytogenetic analysis among the options provided would be peripheral blood. Karyotyping is a cytological technique used to observe an individual's karyotype and requires dividing cells. Peripheral blood contains white blood cells, which can be stimulated to divide in the laboratory environment, a necessary step for cytogenetic analysis. Options such as placenta in formalin, frozen blood plasma, and frozen amniotic fluid are generally not suitable for inducing cell division as required for karyotyping. While the placenta itself is rich in cells, placental tissue in formalin is fixed and therefore no longer capable of cell division, thus not optimal for cytogenetic analysis. Frozen blood plasma and amniotic fluid, when not cryopreserved, may not preserve cells adequately for analysis.