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Snodgrass et al (1966) According to these authors, this malformation complex is due to the aberrant development of the embryonic median fronto-nasal process.In the second category of Snodgrass et al, the facies did not exhibit the prosencephalic type of defect. These patients closely resemble each other and bear little resemblance to category I patients. They show mild microcephaly and micrognathia. The nose is large, with a broad ridge and bulbous tip. There are redundant skin folds in the mandibular and periorbital regions. The mouth may be large and turned down. There are no severe optic defects; cleft lip and palate are not usually observed.We have had the opportunity to do an autoradiographic study on an infant girl with category II D trisomy (Fig. 1). The extra chromosome in this case appears to be a D1 (Fig. 2). Comment Yunis, Hook, and Mayer (1964) proposed that the D group chromosome with late replication in the distal portion of the long arm be designated as D1. The D2 chromosomes in the metaphase were more heavily labelled in the proximal portion, and the D3 chromosomes were the most lightly labelled in the D