Showing papers on "Chromosome 21 published in 1979"

Yeast ribosomal DNA genes are located on chromosome XII

Abstract: Two lines of experimental evidence indicate that the repeating ribosomal DNA (rDNA) genes of the yeast Saccharomyces cerevisiae are located on chromosome XII. First, the rDNA genes are linked mitotically to genes that have been previously mapped to chromosome XII. Second, yeast strains that have two copies of the chromosome containing the rDNA genes in every strain examined also have two copies of chromosome XII; this is not true for the other yeast chromosomes. These data also establish that in mitosis most of the rDNA genes in yeast are not extrachromosomal.

Precise localization of human beta-globin gene complex on chromosome 11

Abstract: Cloned DNA probes were used in combination with a panel of five hybrid cell clones containing a series of different terminal deletions in human chromosome 11 to map precisely the human hemoglobin beta and delta chain structural genes contained on this chromosome. The region of deletion in each clone of the panel has been defined by biochemical, immunologic, and cytogenetic markers. DNA from clones containing successively larger terminal deletions was tested with appropriate DNA probes to determine the point on the chromosome at which DNA for these two closely linked hemoglobin genes is deleted. These genes, and by inference the closely linked G gamma and A gamma globin genes as well, have been assigned to the intraband region 11p1205 leads to 11p1208 on the short arm of chromosome 11, an interval containing approximately 4500 kilobases of DNA. The approach appears to have potential for even greater resolution and reasonably wide applicability for gene mapping.

The role of non-disjunction in aneuploidy in man. An overview.

Abstract: Non-disjunction plays a major role in generating aneuploidy in man. About 50% of spontaneous abortions are chromosomally abnormal and among these, trisomies constitute the major group (∼50%), followed by monosomy X (18%), triploidy (17%), tetraploidy (6%) and others. Over 30% of all trisomies are due to trisomy for chromosome 16. There seems to be an association between maternal radiation history and spontaneous abortions in the sence that the work reported, mothers of chromosomally abnormal foetuses have received higher mean gonadal doses relative to comparable controls. About 6% of babies who die perinatally are chromosomally abnormal and the majority are trisomics especially for group E chromosomes. The results of six major surveys of consecutive newborns show that 6 out of 1000 (0.6%) carry one or another kind of chromosome anomally. The breakdown is as follows: 0.22%, sex-chromosomal abnormalities; 0.14%, autosomal trisomies (+D, +E and +G); 0.19%, balanced structural rearrangements and 0.06%, unbalanced structural rearrangements and others. The frequency of “clinically significant” anomalies has been estimated to be about one-half of the total of all chromosomal abnormalities detected in newborns. The spontaneous “mutation rate” for numerical anomalies of chromosomes which result in liveborn children is about 15 × 10 −4 per gamete per generation (9.3 × 10 −4 for sex-chromosomal aneuploidies and 5.7 × 10 −4 for autosomal trisomies). Autosomal aneuploidies are associated with more severe phenotypic effects than sex-chromosomal aneuploidies. The majority of the sex-chromosomal aneuploidies are constituted by XXY, XYY, XXX and XO genotypes (and mosaics). Of these, while the XYY genotype can arise only through second division paternal non-disjunction, the others can arise as a result of either first or second division non-disjunction in either the father or the mother. There is evidence showing that in about 80% of XO (Turner's syndrome) individuals, the single remaining X is of maternal origin suggesting loss of the paternal-X. The frequency of sex-chromosomal aneuploidies in children born to survivors of the Hiroshima and Nagasaki bombings is higher than in controls, but the difference is not significant. Down's syndrome, which is one of the relatively better known autosomal aneuploidies in man, is due to trisomy for chromosome 21, translocation of chromosome 21 with another autosome (usually chromosome 14) or mosaicism for an extra chromosome 21. Trisomy 21 which accounts for 95% of the cases, is due to non-disjunction during gametogenesis in one of the parents, more often in the mother. With quinacrine fluorescent techniques, evidence has been obtained which shows that non-disjunction can occur either in the father or in the mother at first or second meiotic division. The incidence of primary trisomies for chromosome 21 shows a strong correlation with increasing maternal age and this is very extensively documented (gradual increase in risk from maternal age about 20 to 30–31 and a steeper increase thereafter). The data on the association between an increase in paternal age and Down's syndrome are conflicting although some data suggest that the risk may be high for fathers above 55 years of age. Satellite associations between acrocentric chromosomes have been observed in metaphase preparations of chromosomes of lymphocytes, but the questions of whether there are preferential associations between certain chromosomes, and if so, what their relevance is for trisomy, are not yet settled. Consequently it may be premature to extrapolate the findings in somatic cells to germ cells and to the possible origin of trisomies, including that of trisomy 21. The results of 9 retrospective and 3 prospective studies designed to examine whether parental irradiation may increase the risk of producing Down's syndrome have been published. The available evidence does suggest that there is no correlation between paternal radiation and Down's syndrome in the progeny, but is conflicting on the question of correlation between maternal irradiation and Down's syndrome. Thus, after nearly two decades of work on this aspect, no unequivocal answers are available. Both trisomy 18 (Edward's syndrome) and trisomy 13 (Patau's syndrome) are associated with severe phenotypic effects; the incidence rates are about one on 10 000 and one in 15 000 births, respectively. These trisomies are not compatible with survival to adulthood. Other, relatively rare trisomies include those for chromosomes 8 and 22. In Fig. 1 is presented a broad summary of the frequencies of different chromosomal anomalies and thier effects, relating these to one million conceptions (under the assumption that 15% of all conceptions are spontaneously aborted and 2% of the children die perinatally and making use of the different frequencies cited in the text with respect to the kinds of anomalies). The technique of fusion of human spermatozoa with golden hamster eggs, the details of which were published recently, appears to be a promising one since, this permits a direct analysis of the chromosome constitution of human spermatozoa and hopefully, studies on the effects of physical and chemical agents at a level that has hitherto been impossible.

Assignment of the gene for cytoplasmic superoxide dismutase (Sod-1) to a region of chromosome 16 and of Hprt to a region of the X chromosome in the mouse.

Abstract: In the search for homologous chromosome regions in man and mouse, the locus for cytoplasmic superoxide dismutase (SOD-1; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is of particular interest. In man, the SOD-1 gene occupies the same subregion of chromosome 21 that causes Down syndrome when present in triplicate. Although not obviously implicated in the pathogenesis, SOD-1 is considered to be a biochemical marker for this aneuploid condition. Using a set of 29 mouse—Chinese hamster somatic cell hybrids, we assign Sod-1 to mouse chromosome 16. Isoelectric focusing permits distinction between mouse and Chinese hamster isozymes, and trypsin/Giemsa banding distinguishes mouse from Chinese hamster chromosomes. The mouse fibroblasts used were derived from a male mouse carrying Searle's T(X;16)16H reciprocal translocation in which chromosomes X and 16 have exchanged parts. Analysis of informative hybrids leads to regional assignment of Sod-1 to the distal half of mouse chromosome 16 (16B4 → ter). Because the Chinese hamster cell line (380) used for cell hybridization is deficient in hypoxanthine phosphoribosyltransferase (HPRT; IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8), that part of the mouse X chromosome carrying the complementing Hprt gene can be identified by selection in hypoxanthine/aminopterin/thymidine medium and counterselection in 8-azaguanine. Mouse Hprt is on the XT translocation product containing the proximal region X cen → XD.

The phylogeny of human chromosomes

Abstract: Section I. The Origin of Man.- 1. Man, the Most Intelligent Ape.- The Human Paradox.- Intelligence, Ape and Man.- References.- 2. The Fossil Record and the Emergence of Modern Man.- Africa Versus Asia Darwin Versus Haeckel.- The Fossil Record in Africa.- Yet Man Could Have Emerged in Asia.- Ramapithecus, Dryopithecus and the Great Apes.- From Homo erectus to Homo sapiens.- References.- 3. Man and His Classification.- The Conflict of Organic and Molecular Evolution.- References.- 4. The Theory of Evolution, Genes, and Chromosomes.- Natural Selection and Mendelian Genetics.- Chromosomes, the Vehicles of Inheritance.- References.- Section II. Cytotaxonomy and the Evolution of Man and the Great Apes.- 5. The Chromosomes of Man and the Great Apes. The Inference of Interspecific Homology.- Chromosome Number in the Hominidae.- Comparative Studies with Chromosome Banding Techniques.- 1. G-and R-Banding.- 2. Q-Banding.- 3. C-Banding.- 4. G-11 Staining.- 5. Methylated DNA Sequences.- 6. T-Banding.- 7. Ammoniacal Silver (Ag-AS) Staining.- The Inference of Chromosome Homology Through Different Degrees of Similarity.- 1. Chromosomes with Identical Morphology and G- (or R-) Banding Pattern in All Species.- 2. Chromosomes with Very Similar Morphology in All Species.- 3. Homologous Chromosomes Between Species Which Can Be Derived from Each Other by Chromosome Rearrangement of G- (or R-) Band Regions.- 4. Homologous Chromosomes With a Similar Morphology but With G- Banding Pattern Which Neither Coincides With Nor Can be Derived by Chromosome Rearrangement.- 5. Chromosomes Having no Similar Counterpart in Any Other Species.- The Y Chromosome.- References.- 6. Chromosome Heteromorphisms in Man and the Great Apes as a Source of Chromosome Variation Within Species.- Chromosome Heteromorphisms in Man.- Chromosome Heteromorphisms in the Great Apes.- 1. Chromosome Heteromorphisms in Pan troglodytes.- 2. Chromosome Heteromorphisms in Pan paniscus.- 3. Chromosome Heteromorphisms in Gorilla gorilla.- 4. Chromosome Heteromorphisms in Pongo pygmaeus.- Phylogenetic Implications of Chromosome Variation in the Orangutan.- References.- 7. Chromosome Rearrangement and the Phylogeny of the Hominidae.- Inversions and Telomeric Fusions.- Implications of Chromosome Rearrangement: a Comparison with Other Species.- 1. Inversions.- 2. Translocations and Centric Fission.- 3. Telomeric Fusion.- The Reconstruction of the Ancestral Karyotype of the Hominidae and the Relationship Between Man and the Great Apes.- References.- 8. Chromosome Variation Versus Chromosome Fixation.- Allopatric and Stasipatric Models of Speciation.- References.- Section III. Comparative Gene Mapping And Molecular Cytogenetics. A New Approach to Cytotaxonomy.- 9. Composition of the Human Genome.- Repetitive and Non-Repetitive DNA Sequences.- Palindromes and Tandem Repeats.- Satellite DNA and Sequence Heterogeneity.- References.- 10. Evolution of Non-Repetitive DNA Sequences in Man and the Great Apes.- Nucleotide Substitutions and Phyletic Divergence.- Man and the Great Apes: Phylogenetic Implications.- Is Man an Asian Ape?.- References.- 11. Evolution of Structural Gene Sequences.- Missense Mutations and Amino Acid Substitutions.- Molecular Evolutionary Clocks and the Human-Ape Divergence.- The Maximum Parsimony Approach and the Decelerated Rates of Molecular Evolution in the Higher Primates and Man.- Whence Come Chromosomes?.- References.- 12. Comparative Gene Mapping in Man and Other Primates.- The Evolution of Chromosomes as Syntenic Groups.- The Conservation of the Syntenic Groups Among the Hominidae and Cercopithecoidea.- Comparative Gene Mapping Between Hominidae-Cercopithe- coidea and the Possible Origin of Chromosome 1 in Man.- Are Chromosomes Frozen Accidents?.- Gene Duplication, Polyploidy, and Evolutionary Frozen Chromosomes.- References.- 13. Evolution of Repetitive DNA Sequences in Man and Other Primates.- Repetitive DNA in the Primates.- Repetitive DNA in Man.- Satellite DNAs in Man and Other Organisms. Possible Explanations of Their Evolutionary Conservation.- References.- 14. The Chromosome Distribution of Homologous Sequences to the Four Human Satellite DNAs in the Hominidae.- The Distribution of Satellite I, II, III and IV in the Human Chromosome Complement.- The Distribution of Homologous Sequences to the Four Human Satellite I, II, III, and IV DNA in the Chromosome Complement of the Great Apes.- Interspecific Chromosome Homologies in the Hominidae in Relation to Hybridisation. Independent Amplification of Highly Repetitive DNAs After Speciation.- References.- 15. DNA Composition of Constitutive Heterochromatin in the Chromosome Complement of Man and the Great Apes.- Constitutive Heterochromatin as Demonstrated by C-Banding.- G-11 Regions and Satellite III-Rich Regions.- References.- 16. The Chromosomal Distribution of Ribosomal Genes in Man and the Great Apes.- rDNA Genes in Man.- 18S and 28S Cistrons in the Great Apes and Other Primates.- 5S rDNA Cistrons in Man and the Great Apes.- References.- 17. Late DNA Replicating Patterns in the Chromosomes of Man and the Great Apes.- DNA Replication at the Chromosome Level.- DNA Replication Sites in Relation to Chromosome Banding.- The X Chromosome.- Euchromatin, Heterochromatin and DNA Replication.- References.- 18: Evolution of Genome Size in Man and the Great Apes.- The DNA Content of Man and Other Organisms.- Why Has DNA Content Changed?.- References.

Assignment of human beta-, gamma-, and delta-globin genes to the short arm of chromosome 11 by chromosome sorting and DNA restriction enzyme analysis

Abstract: Normal human metaphase chromosomes isolated from fibroblasts were resolved into 14 peaks based on total Hoechst 33258 fluorescence and sorted with the fluorescence-activated cell sorter. The chromosomal DNA was extracted and characterized by EcoRI analysis. As expected, analysis of the peak containing chromosomes 16 and 18 detected the alpha-globin genes and of the peak containing chromosomes 9, 10, 11, and 12 detected the beta-, gamma-, and delta-globin genes. Translocations were then used to localize further the beta-, gamma-, and delta-globin genes. The first translocation t(11;22)(q25;q11), which moved nearly all of chromosome 11 to a different peak, confirmed that the beta-, gamma-, and delta-globin genes are on this chromosome. The second, t(4;11)(q25;q13), which moved the distal portion of the long arm of chromosome 11 to a new peak, showed that the genes are not in this segment. The third, t(X;11)(q11;p13), moved the distal region of the short arm of chromosome 11 to a peak which now contained the beta-, gamma-, and delta-globin genes. Therefore, the beta-, gamma-, and delta-globin genes residue on the distal portion of the chromosome 11 short arm including bands p13, p14, and p15. This sorting method may be used generally to assign other genes to chromosomal segments of the entire chromosome complement.

Evidence for a correlation between late replication and autosomal gene inactivation in a familial translocation t(X;21).

Abstract: A familial translocation t(X;21)(q2700;q11) is studied. A girl, trisomic for almost all the chromosome 21, has a mildly abnormal phenotype. A second girl, phenotypically abnormal, is monosomic for the juxtacentromeric region of chromosome 21 only. A comparison of the replication pattern and of the activity of superoxide dismutase (gene located on chromosome 21) shows a clear correlation between late replication, gene inactivation and phenotype expression of chromosome 21.

Origin of the extra chromosome in trisomy 21.

Abstract: Of 61 families of children with trisomy 21, polymorphism of chromosome 21 elucidating the origin of the extra chromosome was found in 42. Nondisjunction was of paternal origin in 8 cases (19.04%) and the anomaly occurred with equal frequency during the first and second meiotic divisions. Maternal nondisjunction was demonstrated in 34 cases (80.95%), in which nondisjunction occurred by far the most often during the first meiotic division (29 cases). These results are in agreement with data from the literature, and suggest the existence of at least two different causes for chromosomal nondisjunction, the first being the same in both sexes and occurring in both meiotic divisions and the second specifically limited to the first meiotic division in the mother.

Regional localization of human gene loci on chromosome 9: studies of somatic cell hybrids containing human translocations.

Abstract: Somatic cell hybrids were derived from the fusion of (1) Chinese hamster cells deficient in hypoxanthine guanine phosphoribosyltransferase (HPRT) and human cells carrying an X/9 translocation and (2) Chinese hamster cells deficient in thymidine kinase (TK) and human cells carrying a 17/9 translocation. Several independent primary hybrid clones from these two series of cell hybrids were analyzed cytogenitically for human chromosome content and electrophoretically for the expression of human markers known to be on human chromosome 9. The results allow the assignment of the loci for the enzymes galactose-1-phosphate uridyltransferase (GALT), soluble aconitase (ACONs), and adenylate kinase-3 (AK3) to the short arm of chromosome 9 (p11 to pter) and the locus for the enzyme adenylate kinase-1 (AK1) to the distal end of the long arm of human chromosome 9 (hand q34). Earlier family studies have shown that the locus for AK1 is closely linked to the ABO blood group locus and to the locus of the nail-patella (Np) syndrome. Thus the regional localization of AK1 locus permits the localization of the AK1-Np-ABO linkage group.

Down syndrome: Gene dosage at the transcriptional level in skin fibroblasts

Abstract: Chromosome imbalance (aneusomy) is the leading known cause of both spontaneous abortion and mental retardation in human beings. The primary abnormality is thought to result from quantitative changes of transcription products from the unbalanced genetic material. To document this point, I compared chromosome 21-specific transcription in skin fibroblasts from subjects with monosomy 21, disomy 21 (normal), and trisomy 21 (Down syndrome). Polyadenylylated RNA [poly(A)-RNA], which is enriched in messenger and messenger-precursor RNA sequences, was isolated from the above fibroblast lines. Radioactive DNA (cDNA) complementary to these RNAs was synthesized with reverse transcriptase (RNA-dependent DNA polymerase). These cDNAs were hybridized with (i) DNA from a cell line with a mouse genome plus human chromosome 21 and (ii) mouse DNA. Subtraction of the amount of hybridization in experiment ii from that in experiment i yielded a measure of human chromosome 21-specific RNA sequences. The results were consistent with gene dosage at the transcriptional level; for monosomy 21-derived cDNA, 0.6% (of the total cDNA) hybridized specifically to human chromosome 21; for disomy 21-derived cDNA, 2% hybridized; and for trisomy 21-derived cDNA, 3% hybridized. Thus, for DNA sequences on chromosome 21 in human skin fibroblasts, transcription depends on DNA dosage. Characterization of the chromosome 21-specific RNA sequences quantitated in these experiments could help to elucidate the mechanisms by which abnormal karyotypes result in abnormal phenotypes.

Partial purification and characterization of DNA from the human X chromosome

Abstract: Human X chromosome DNA was partially purified from a mouse-human hybrid cell line containing a single human chromosome, the X. Enrichment of such DNA was accomplished by two sequential reassociations of radiolabeled hybrid cell DNA with large excesses of mouse DNA. Unreassociated hybrid cell DNA was used as a probe for human X chromosome sequences. The human-specific fraction of probe DNA CONTAINED THREE COMPONENTS. Two of these reassociated to human DNAs at rates proportional to the number of X chromosomes present. These two components were thus localized to the X chromosome. One of these X-specific components, representing about 80% of human-specific probe DNA, consisted of single copy or very low order reiterated DNA. The second X-specific component, representing about 10% of human-specific probe DNA, was about 20-30 times more reiterated. The remaining 10% of human-specific probe DNA, although derived from the X chromosome, reassociated to human DNAs at a rate independent of the number of X chromosomes present. This component was thus homologous to autosomal as well as X chromosome DNA. The probe DNA accounts for approximately half of the human X chromosome, suggesting that the remainder may have homology with mouse DNA.

The Genetic and Cytogenetic Localization of the Three Structural Genes Coding for the Major Protein of Drosophila Larval Serum

Abstract: The α, β and γ polypeptides that make up Drosophila Larval Serum Protein-1 seem to be coded for by genes that have evolved by duplication of a common ancestral gene. We have found variants of all three polypeptides, and these are variants of the coding sequences. The α-chain variant mapped to 39.5 on the X chromosome and to the polytene interval 11A7-11B9. The β-chain variant mapped to 1.9 on chromosome 2L and to 21D2-22A1. The γ-chain variant was mapped as 0.13 map units from the tip of chromosome 3L or to —1.41 with respect to ru, which has been defined as 0.0, and to 61A1-61A6.

Fragile site long arm chromosome 16

Abstract: A fragile site at the long arms (q21) of chromosome 16 was found in two persons, each of whom became the parent of a child with a de novo structural chromosome abnormality--a balanced autosomal translocation and an autosomal deletion. The question of an increased risk of structural chromosome abnormalities in the offspring of persons with fragile site long arm 16 is discussed.

Site-specific instability in Drosophila melanogaster: the origin of the mutation and cytogenetic evidence for site specificity.

Abstract: During a study of delayed mutations, an unstable X chromosome (Uc) was detected. Spontaneous X-linked recessive lethal mutations were detected in 34 of 993 sperm sampled from 50 males carrying this chromosome. All but three of the 34 lethals originated as clusters in three of the 50 males Cytogenetic and complementation analyses revealed 14 intrachromosomal rearrangements: ten inversions, two reverse repeats, one deficiency and one transposition. Eight of the 14 rearrangements have one break in the 6F1–2 doublet and two rearrangements have a break in 6F1–5 of the X chromosome. The remaining four rearrangements have in addition to the aberrations a lethal point mutation between 6F1 and 6F5. Though each of the lethal lines was established from a single lethal-bearing female, chromosome polymorphism is evident in 17 of the 18 lines having rearrangements, with certain aberrations recurring in several lines. The lethal mutations revert frequently to the nonlethal state, and cytological evidence indicates that more than one mutational event may occur at the unstable locus of the chromosome during one generation. Two lethal lines had more than one type of chromosome rearrangement sharing a common breakpoint. These observations are consistent with the view that the instability in the Uc lines is caused by a transposable element capable of site-specific chromosome breaks and perpetual generation of mutations. The mutagenic and genetic properties of transposable elements can be related to the two-mutation theory of Knudson (1971) for cancer initiation.

Reproductive risk of t(13q14q) carriers: Case report and review

Abstract: We report a four-generation kindred with a balanced 13q 14q Robertsonian translocation The proband had the Down syndrome, due to trisomy of chromosome 21; he also carried the balanced D-group translocation A segregation analysis of 86 sibships was performed to examine the risk of t(13q 14q) carrier parents having trisomy 21, 47, XXY, or trisomy 13 children by which a number of families were ascertained None of these disorders recurred after birth of the propositi The frequency of abortions was not different from that of the general population The conditional segregation ratio for balanced translocation carriers among the phenotypically normal offspring of carrier parents was 055 ± 004

Non‐random duplication of chromosome 15 in murine T‐cell leukemias induced in mice heterozygous for translocation 1(14:15)6

Abstract: Trisomy of chromosome 15 is a highly regular feature of murine T-cell leukemogenesis. We have studied the chromosomal constitution of 7,12-dimethylbenza(a)anthracene (DMBA)-induced T-cell leukemias in C57BL X CBAT6T6 F1 mice. The CBAT6T6-derived chromosome T(14:15)6 was regularly duplicated whereas the C57BL-derived normal chromosome 15 was only present in one copy. It was concluded that the gene(s) that tend to duplicate in parallel with the neoplastic transformation of the prothymocyte to an overt leukemic cell have a greater chance of duplicating and/or may have a stronger promoting effect on leukemogenesis if stronger promoting effect on leukemogenesis if located on the CBA-derived, structurally rearranged T(14:15)6 than the corresponding genes located on the C57BL-derived normal chromosome 15.

Two cases of trisomy 12p due to rcpt (12;21)(p11;p11) inherited through three generations.

Abstract: Two cases of trisomy 12p due to a familial translocation t(12;21) (p11;p11) inherited through three generations are presented. The clinical features of both affected individuals are consistent with those previously reported. Study of the NORs by silver staining showed translocation of the NOR from chromosome 21 onto the der(12) and suggested that the activity of this site has been suppressed in some carriers.

Normal phenotype and partial trisomy for the G positive region of chromosome 21.

Abstract: A prenatally diagnosed male fetus and his mother, who was referred because of her advanced age, both carried an abnormal bisatellited chromosome 21 as an extra chromosome. The abnormal 21 was monocentric and the G negative band q22 and part of q21 had been deleted during formation. The phenotype of both the mother and child (at birth) was normal.

Familial partial 7q monosomy resulting from segregation of an insertional chromosome rearrangement.

Abstract: A family with an insertional type of chromosome rearrangement involving chromosomes 7 and 13 is reported. An interstitial deletion of a segment of chromosome 7 (7q32 leads to 34) had been inserted into the long arm of chromosome 13 at breakpoint q32. Segregation of this chromosome rearrangement gave rise to three subjects who were monosomic for the involved segment of chromosome 7. The karyotypes were: 46,XX, or XY,der(7)ins(13;7) (q32;q32q34). All three subjects were mentally retarded and had minor dysmorphic features. The Kidd, Colton, and Kell blood group systems were investigated, but were not informative.

Monosomy 21: a possible stepwise evolution of the karyotype.

Abstract: We describe a female infant with manifestations of complete monosomy for chromosome 21 intrauterine growth retardation, failure to thrive, craniofacial anomalies, arthrogryposis-like features, and psychomotor retardation. Chromosome analysis demonstrated mosaicism for three different cell lines in the various tissues examined; 45,XX,–21/46,XX,del(21)(q11) 46,XX. The existence of these three lines suggests a possible explanation for the few cases of “complete monosomy 21” which have been reported.

A chromosomal abnormality (21q-) in primary thrombocytosis.

Abstract: A patient with primary thrombocytosis was found to present an acquired deletion of the long arm of chromosome 21 (21q-) A similar observation reported in the literature is hereby confirmed

Unstable transpositions of his4 in yeast

Abstract: Unstable transpositions in yeast have been selected in which the his4C gene from chromosome III is inserted into chromosome XII. This event is associated with the generation of a recessive lethal mutation, resulting from the integration of his4C into an essential gene. Strains with these transpositions are viable as diploids or aneuploids for chromosome XII. The event that generates the transpositions does not lead reciprocally to a deletion on chromosome III, implying that synthesis of a new copy of his4C and subsequent transposition may have occurred. The his4C transpositions are unstable and give rise to C- segregants at a high frequency, as a result of either precise excision of the his4C gene (restoring function of the gene into which insertion had occurred) or chromosome loss.

Partial trisomy 17q. Karyotype: 46,XY,der(21),t(17;21)(q22;p13).

Abstract: A 15-year-old deeply mentally retarded male is described with partial distal 17q trisomy (17q22→17qter), as the result of a de novo 17q/21p translocation. Differential Ag-staining showed that the satellites of chromosome 21 were included in the translocation chromosome.

Interchromosomal effects of heterochromatic deletions on recombination in Drosophila melanogaster.

Abstract: It is now known that partial deletions of the satellite sequences in X - chromosome heterochromatin result in a significant decrease in intrachromosoma1 recombination in the proximal region of the X chromosome of D. melanogaster (YAMAMOTO and MIKLOS 1978). It is important to ask then if the loss or gain of heterochromatin on the X also alters recombination in other chromosomes of the genome (interchromosomal effects). I have looked for such alterations by measuring recombination in chromosome 3. The results clearly indicate that the partial loss of X -chromosome heterochromatin not only decreases crossing over in the proximal region of the X chromosome itself, but also increases the frequency in chromosome 3. especially in the euchromatic regions around the centromere. Furthermore, the greater the deficiency of X heterochromatin, the higher is recombination in chromosome 3 . This finding not only provides further evidence in support of the hypothesis that heterochromatin, in this case mainly composed of satellite DNA, regulates the recombination system, but it demonstrates that when the satellite content of one chromosome of the D. melanogasier genome is altered, there is an alteration in the crossover characteristics of other chromosomes in the same complement. If the amount of satellite DNA in a genome is being continuously altered, then one can predict that the recombination system is also being continually perturbed. Thus, the changing gene Combinations produced indirectly by increases or decreases of heterochromatin are among the components available to organisms to break up or form new gene combinations upon which se!ection can act.

Colinearity in the mouse genome: a study of chromosome 2.

Abstract: The cytologic positions (determined by G-banding) of the breakpoints on mouse chromosome 2 of a series of ten reciprocal translocations were compared with their most probable genetic positions on the linkage map, as determined by studies on recombination with known chromosome 2 (= linkage group V) markers. The most probable proximaldistal orders of the genetic and cytologic breakpoints were found to be the same; i.e., the two sets of breakpoints were colinear. However, there was no close correspondence between these two measures of the distance apart of adjacent breakpoints, since some translocation breaks which were well separated in G-band positions seemed close together in terms of the linkage map, and vice versa. This helps to confirm LYON'S conclusion that in certain mouse chromosomes, including No. 2, the distribution of chiasmata is nonrandom.

X-linkage of a human genetic locus that corrects the DNA synthesis lesion in tsC1AGOH mouse cells.

Abstract: GM 126 human diploid fibroblasts were fused with a heat-sensitive mouse cell mutant defective in DNA synthesis, and primary hybrids were selected at permissive and nonpermissive temperatures in HAT medium. Primary hybrids, primary hybrid clones back-selected in 8-azaguanine at the permissive temperature, and subclones of heat-resistant primary hybrids isolated under nonselective conditions or after 8-azaguanine treatment were tested for heat sensitivity, the expression of 26 human enzymes assigned to 19 different human chromosomes, and the presence of human chromosomes. Only the human X chromosome and X-linked marker enzymes exhibited a clear pattern of concordant segregation with the heat-resistant phenotype. On the basis of these observations, we have defined the human genetic locus that corrects the heat-sensitive lesion in tsC1AGOH as hrC1AGOH and have assigned this locus to the X chromosome. This observation provides the first instance where two selectable markers (heat resistance and 8-azaguanine sensitivity) are found on a single human chromosome and suggests that these markers may prove to be a valuable push-pull selective system of use in determining the linear arrangement of genes on human chromosomes by somatic cell genetics.

Abnormal children of a 47,XYY father.

Abstract: Abnormal children of two 47,XYY men were studied. One of these men had 2 normal daughters and a child, 45,X/46,XY, with gonadal dysgenesis. The other man had 2 normal sons and a child with Down's syndrome. The extra chromosome 21 of this child came from the mother. Another 47,XYY man had 4 normal children.

Familial translocation t(10;21)(q22;q22).

Abstract: A family is described with a translocation t(10;21)(q22;q22) transmitted through three generations. This family was studied for the apparition of several miscarriages and two sisters with multiple malformations. Both children had a probably partial trisomy of chromosome 10 and a monosomy of chromosome 21 due to a maternal adjacent-2 meiotic segregation.