Flattened metaphase figures were obtained by squashing or air-drying cells from human leucocyte cultures that had been treated with colchicine and hypotonic sodium citrate prior to fixation. In such metaphase figures the Y chromosome was at the periphery of the figure more often than chance expectation and more often than the chromosome pairs 1, 2, or 16 or the chromosome groups 13–15, 17–18, 19–20, or 21–22. The Y chromosome was further from the center of circular metaphase figures than the mean value of all the chromosomes or the chromosome pairs 1, 2, or 3 or the chromosome groups 4–5, 6–12+X, 19–20 or 21–22.
Summary. A familial reciprocal translocation t(6p + ;l lq-) is presented, unbalanced (6p +) in the craniorachischisic propositus and balanced in his phenotypically normal father, associated with relative infertility, multiple spontaneous abortions, and failure to produce normal offspring. The karyotype-phenotype relationship is discussed with reference to other published cases of partial trisomy for the distal portion of the long arm of chromosome 11, and the concept of deletionunmasking is briefly considered. The occurrence of major neural groove closure defects due to a variety of translocations in mice is noted. The gametic segregation of balanced and unbalanced karyotypes is unique to each particular translocation making recurrence risk projections hazardous in the absence of prior experience with the particular translocation. The questions of the relative importance of genetic inheritance, chromosomal abnormalities, and many environmental factors including possible specific teratogens in causing neural groove closure anomalies are still unsettled. The paucity of published chromosome studies in these malformations is noted. We urge that cytogenetic studies with banding techniques be undertaken on these cases and their parents in order to expand basic knowledge of the role of chromosomal errors in their aetiology.Craniorachischisis, which combines anencephaly and total spina bifida with meningomyelocele, is the extreme example of defective neural groove closure. Because of their apparent anatomical and epidemiological similarity and the frequency with which one type may be born to a family which has already had another, defects such as craniorachischisis, anencephaly, spina bifida, meningomyelocele, and hydrocephalus are frequently considered together in attempts to elucidate their causes. Anencephaly is the most common and shows wide variation in incidence geographically and ethnically (Green, 1964), rang-
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