Faculty Bibliography

Given the DNA fingerprints of two individuals with some bands being shared by both individuals, we define a new measure of the degree of similarity between the DNA profiles of two individuals. We use this measure to calculate the expected DNA similarity of two unrelated individuals of a randomly mating population; this similarity is due to chance only. Then, the expected similarity between two related individuals is obtained; this similarity is due to chance and relatedness. From these results, the degree of similarity due to relatedness alone may be calculated.

We have studied DNA polymorphisms at loci in the pericentromeric region on the long arm of chromosome 21 in 200 families with trisomy 21, in order to determine the meiotic origin of nondisjunction. Maintenance of heterozygosity for parental markers in the individual with trisomy 21 was interpreted as resulting from a meiosis I error, while reduction to homozygosity was attributed to a meiosis II error. Nondisjunction was paternal in 9 cases and was maternal in 188 cases, as reported earlier. Among the 188 maternal cases, nondisjunction occurred in meiosis I in 128 cases and in meiosis II in 38 cases; in 22 cases the DNA markers used were uninformative. Therefore meiosis I was responsible for 77.1% and meiosis II for 22.9% of maternal nondisjunction. Among the 9 paternal nondisjunction cases the error occurred in meiosis I in 2 cases (22.2%) and in meiosis II in 7 (77.8%) cases. Since there was no significant difference in the distribution of maternal ages between maternal I error versus maternal II error, it is unlikely that an error at a particular of maternal ages between maternal I error versus maternal II error, it is unlikely that an error at a particular meiotic stage contributes significantly to the increasing incidence of Down syndrome with advancing maternal age. Although the DNA polymorphisms used were at loci which map close to the centromere, it is likely that rare errors in meiotic-origin assignments may have occurred because of a small number of crossovers between the markers and the centromere.(ABSTRACT TRUNCATED AT 250 WORDS)

A genetic linkage map of the human genome was constructed that consists of 1416 loci, including 279 genes and expressed sequences. The loci are represented by 1676 polymorphic systems genotyped with the CEPH reference pedigree resource. A total of 339 microsatellite repeat markers assayed by PCR are contained within the map, and of the 351 markers with heterozygosities of at least 70%, 205 are microsatellites. Seven telomere loci define physical and genetic endpoints for 2q, 4p, 7q, 8p, 14q, 16p, and 16q, and in other cases distal markers on the maps have been localized to terminal cytogenetic bands. Therefore, at least 92% of the autosomal length of the genome and 95% of the X chromosome is estimated to be spanned by the map. Since the maps have relatively high marker density and numerous highly informative loci, they can be used to map disease phenotypes, even for those with limited pedigree resources. The baseline map provides a foundation for achieving continuity of clone-based physical maps and for the development of a truly integrated physical, genetic, and cytogenetic map of the human.

This report presents cytogenetic data on three cases of malignant ovarian germ cell tumors. All were diagnosed as malignant teratoma; case 1 with yolk sac elements; case 2 with elements of endodermal sinus tumor, embryonal carcinoma, and choriocarcinoma; and case 3 with yolk sac elements and embryonal carcinoma. Metaphase cells from each tumor, and normal tissue from the host, were karyotyped and scored for centromeric heteromorphisms in an attempt to determine the mechanism of origin. The karyotypes were 79,XXX,+1,+3,-6,+8,+12,+14,-15,+17, +20,+21,+22;49,XX,+8,+12,+22; and 48,XX,+3,+14, respectively. The analysis of centromeric heteromorphisms and DNA fingerprints of host and teratoma using the M13 probe revealed that one case originated from a germ cell before the first meiotic division. Normal host tissue was not available in case 2, but several centromeric markers were heterozygous in the tumor, indicating either meiosis I error or complete failure of germ cell meiosis. In the third case the centromeric heteromorphisms that were heterozygous in the host appeared to be homozygous for certain chromosomes and heterozygous for others in the tumor. These results suggest that germ cell teratomas could arise by the fusion of two ova.

A genetic case-control study was conducted in a group of patients with schizophrenia (n = 67; DSM-III) and psychiatrically normal controls matched for ethnicity (n = 84), living in the same geographical area. Using three different DNA polymorphisms of the gene encoding porphobilinogen deaminase (PBGD), a candidate gene for schizophrenia, an association with schizophrenia could not be detected. No significant associations were detected even after sub-division of the cohort by ethnicity and by gender.

Microsatellite DNA consists of tandemly repeated simple DNA sequence motifs, the number of these repeats being polymorphic. These recently described polymorphisms are ubiquitously distributed throughout the human genome and are highly informative, making them ideal markers for linkage analysis. Physical localization of these microsatellites is an important prerequisite for aligning physical and genetic maps. We have physically mapped the microsatellite at D13S71, which has previously been assigned to chromosome 13. Band-specific mapping of D13S71 to the distal part of band 13q32, near 13q33, was achieved by microdissection of GTG-banded chromosomes and subsequent enzymatic amplification with a heminested PCR approach. Analysis of a panel of somatic cell hybrids confirmed this localization. The technique presented may also be useful in a variety of complex mapping situations and whenever the precise localization of very small (as small as 70 bp) DNA probes is necessary.