Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Whole-genome sequencing of dog-specific assemblages C and D of Giardia duodenalis from single and pooled cysts indicates host-associated genes
    Kooyman, Frans N.J. ; Wagenaar, Jaap A. ; Zomer, Aldert - \ 2019
    Microbial Genomics 5 (2019)12. - ISSN 2057-5858
    cathepsin - diplomonad - heterozygosity - multiple displacement amplification - parasitology - synteny

    Giardia duodenalis (syn. Giardia intestinalis or Giardia lamblia) infSAects over 280 million people each year and numerous animals. G. duodenalis can be subdivided into eight assemblages with different host specificity. Unculturable assemblages have so far resisted genome sequencing efforts. In this study, we isolated single and pooled cysts of assemblages C and D from dog faeces by FACS, and sequenced them using multiple displacement amplification and Illumina paired-end sequencing. The genomes of assemblages C and D were compared with genomes of assemblages A and B from humans and assemblage E from ruminants and pigs. The genomes obtained from the pooled cysts and from the single cysts were considered complete (>99 % marker genes observed) and the allelic sequence heterozygosity (ASH) values of assemblages C and D were 0.89 and 0.74 %, respectively. These ASH values were slightly higher than for assemblage B (>0.43 %) and much higher than for assemblages A and E, which ranged from 0.002 to 0.037 %. The flavohaemoglobin and 4Fe-4S binding domain family encoding genes involved in O2 and NO detoxification were only present in assemblages A, B and E. Cathepsin B orthologs were found in all genomes. Six clades of cathepsin B orthologs contained one gene of each genome, while in three clades not all assemblages were represented. We conclude that whole-genome sequencing from a single Giardia cyst results in complete draft genomes, making the genomes of unculturable Giardia assemblages accessible. Observed differences between the genomes of assemblages C and D on one hand and the assemblages A, B and E on the other hand are possibly associated with host specificity.

    Genome-wide population structure and admixture analysis reveals weak differentiation among Ugandan goat breeds
    Onzima, R.B. ; Upadhyay, M.R. ; Mukiibi, R. ; Kanis, E. ; Groenen, M.A.M. ; Crooijmans, R.P.M.A. - \ 2018
    Animal Genetics 49 (2018)1. - ISSN 0268-9146 - p. 59 - 70.
    breed composition - breed diversity - Capra hircus - heterozygosity - indigenous goats - population genetics
    Uganda has a large population of goats, predominantly from indigenous breeds reared in diverse production systems, whose existence is threatened by crossbreeding with exotic Boer goats. Knowledge about the genetic characteristics and relationships among these Ugandan goat breeds and the potential admixture with Boer goats is still limited. Using a medium-density single nucleotide polymorphism (SNP) panel, we assessed the genetic diversity, population structure and admixture in six goat breeds in Uganda: Boer, Karamojong, Kigezi, Mubende, Small East African and Sebei. All the animals had genotypes for about 46 105 SNPs after quality control. We found high proportions of polymorphic SNPs ranging from 0.885 (Kigezi) to 0.928 (Sebei). The overall mean observed (HO) and expected (HE) heterozygosity across breeds was 0.355 ± 0.147 and 0.384 ± 0.143 respectively. Principal components, genetic distances and admixture analyses revealed weak population sub-structuring among the breeds. Principal components separated Kigezi and weakly Small East African from other indigenous goats. Sebei and Karamojong were tightly entangled together, whereas Mubende occupied a more central position with high admixture from all other local breeds. The Boer breed showed a unique cluster from the Ugandan indigenous goat breeds. The results reflect common ancestry but also some level of geographical differentiation. admixture and f4 statistics revealed gene flow from Boer and varying levels of genetic admixture among the breeds. Generally, moderate to high levels of genetic variability were observed. Our findings provide useful insights into maintaining genetic diversity and designing appropriate breeding programs to exploit within-breed diversity and heterozygote advantage in crossbreeding schemes.
    Direct fitness benefits explain mate preference, but not choice, for similarity in heterozygosity levels
    Zandberg, Lies ; Gort, Gerrit ; Oers, Kees van; Hinde, Camilla A. - \ 2017
    Ecology Letters 20 (2017)10. - ISSN 1461-023X - p. 1306 - 1314.
    Great tit - heterozygosity - mate choice - mate preferences - relatedness - reproductive success - sexual selection

    Under sexual selection, mate preferences can evolve for traits advertising fitness benefits. Observed mating patterns (mate choice) are often assumed to represent preference, even though they result from the interaction between preference, sampling strategy and environmental factors. Correlating fitness with mate choice instead of preference will therefore lead to confounded conclusions about the role of preference in sexual selection. Here we show that direct fitness benefits underlie mate preferences for genetic characteristics in a unique experiment on wild great tits. In repeated mate preference tests, both sexes preferred mates that had similar heterozygosity levels to themselves, and not those with which they would optimise offspring heterozygosity. In a subsequent field experiment where we cross fostered offspring, foster parents with more similar heterozygosity levels had higher reproductive success, despite the absence of assortative mating patterns. These results support the idea that selection for preference persists despite constraints on mate choice.

    The scent of inbreeding: a male sex pheromone betrays inbred males
    Bergen, E. van; Brakefield, P.M. ; Heuskin, S. ; Zwaan, B.J. ; Nieberding, C.M. - \ 2013
    Proceedings of the Royal Society. B: Biological Sciences 280 (2013)1758. - ISSN 0962-8452
    butterfly bicyclus-anynana - mate-choice - drosophila-melanogaster - male courtship - genetic load - teleogryllus-commodus - morphological traits - life-history - depression - heterozygosity
    Inbreeding depression results from mating among genetically related individuals and impairs reproductive success. The decrease in male mating success is usually attributed to an impact on multiple fitness-related traits that reduce the general condition of inbred males. Here, we find that the production of the male sex pheromone is reduced significantly by inbreeding in the butterfly Bicyclus anynana. Other traits indicative of the general condition, including flight performance, are also negatively affected in male butterflies by inbreeding. Yet, we unambiguously show that only the production of male pheromones affects mating success. Thus, this pheromone signal informs females about the inbreeding status of their mating partners. We also identify the specific chemical component (hexadecanal) probably responsible for the decrease in male mating success. Our results advocate giving increased attention to olfactory communication as a major causal factor of mate-choice decisions and sexual selection
    Targeted Resequencing of 9p in Acute Lymphoblastic Leukemia Yields Concordant Results with Array CGH and Reveals Novel Genomic Alterations
    Sarhadi, V.K. ; Lahti, L.M. ; Scheinin, I. ; Tyybäkinoja, A. ; Savola, S. ; Usvasalo, A. ; Räty, R. ; Elonen, E. ; Saarinen-Pihkala, U.M. ; Knuutila, S. - \ 2013
    Genomics 102 (2013)3. - ISSN 0888-7543 - p. 182 - 188.
    gene - cancer - heterozygosity - association - expression - deletions - growth
    Genetic alterations of the short arm of chromosome 9 are frequent in acute lymphoblastic leukemia. We performed targeted sequencing of 9p region in 35 adolescent and adult acute lymphoblastic leukemia patients and sought to investigate the sensitivity of detecting copy number alterations in comparison with array comparative genomic hybridization (aCGH), and besides, to detect novel genetic anomalies. We found a high concordance of copy number variations (CNVs) as detected by next generation sequencing (NGS) and aCGH. By both methodologies, the recurrent deletion at CDKN2A/B locus was identified, whereas NGS revealed additional, small regions of CNVs, seen more frequently in adult patients, while aCGH was better at detecting larger CNVs. Also, by NGS, we detected novel structural variations, novel SNVs and small insertion/deletion variants. Our results show that NGS, in addition to detecting mutations and other genetic aberrations, can be used to study CNVs
    Levels of inbreeding in group mating captive broodstock populations of Common sole, (Solea solea), inferred from parental relatedness and contribution
    Blonk, R.J.W. ; Komen, J. ; Kamstra, A. ; Crooijmans, R.P.M.A. ; Arendonk, J.A.M. van - \ 2009
    Aquaculture 289 (2009)1-2. - ISSN 0044-8486 - p. 26 - 31.
    vissen - tong (vis) - voortplanting - natuurlijke paring - populatiegenetica - nageslacht - inteelt - kuitschieten - afstamming - heterozygotie - genetische diversiteit - genetische bronnen - fishes - dover soles - reproduction - natural mating - population genetics - progeny - inbreeding - spawning - parentage - heterozygosity - genetic diversity - genetic resources - cod gadus-morhua - fish breeding programs - dover sole - spawning aggregations - scophthalmus-maximus - reproductive success - genetic-variation - mass selection - dna markers - senegalensis
    In this paper, we estimate levels of inbreeding with parental relatedness and contribution inferred from microsatellites in groups of Common sole that reproduce by natural mating. We present results on spawning patterns during one entire reproductive season of wild Common sole, Solea solea, kept in two broodstock groups (28 animals in broodstock A; 20 animals in broodstock B) under semi-natural conditions. Batches of eggs were collected daily and incubated separately. First, we performed a parentage analysis on parents and samples of 24 newly hatched larvae from all batches, using 10 polymorphic microsatellite markers. As expected, contribution of parents to offspring was highly skewed. In both broodstocks, five or less parental pairs produced more than half of the total progeny. Natural spawning and unequal contributions of parents to offspring resulted in significant deviations from Hardy–Weinberg equilibria. Furthermore, few alleles were lost and levels of heterozygosity in offspring population increased. Next, we calculated relatedness between parents that mated successfully based on estimates of molecular similarity. Mean coefficients of coancestry in offspring were determined using parental relatedness and contributions. Levels of coancestry in progeny were substantially high. These results show that due to different parental contributions, natural mating in groups can result in significant inbreeding in future generations despite of limited loss of alleles and high levels of heterozygosity in first generation progeny. This shows that using loss of alleles and levels of heterozygosity alone can be misleading for estimation of genetic diversity.
    Genome wide diversity: variation over a genome
    Engelsma, Krista - \ 2008
    genetic diversity - genomes - heterozygosity - markers - animal breeding - haplotypes
    Biodiversity of pig breeds from China and Europe estimated from pooled DNA sample differences in microsatellite variation between two areas of domestication
    Megens, H.J.W.C. ; Crooijmans, R.P.M.A. ; SanChristobal, M. ; Hui, X. ; Li, N. ; Groenen, M.A.M. - \ 2008
    Genetics, Selection, Evolution 40 (2008). - ISSN 0999-193X - p. 103 - 128.
    dierveredeling - varkens - varkensrassen - rasverschillen - biodiversiteit - genetische afstand - genetische merkers - heterozygotie - microsatellieten - dna - china - europa - animal breeding - pigs - pig breeds - breed differences - biodiversity - genetic distance - genetic markers - heterozygosity - microsatellites - dna - china - europe - phylogenetic trees - genetic distances - diversity - frequency - markers - models
    Microsatellite diversity in European and Chinese pigs was assessed using a pooled sampling method on 52 European and 46 Chinese pig populations. A Neighbor Joining analysis on genetic distances revealed that European breeds were grouped together and showed little evidence for geographic structure, although a southern European and English group could tentatively be assigned. Populations from international breeds formed breed specific clusters. The Chinese breeds formed a second major group, with the Sino-European synthetic Tia Meslan in-between the two large clusters. Within Chinese breeds, in contrast to the European pigs, a large degree of geographic structure was noted, in line with previous classification schemes for Chinese pigs that were based on morphology and geography. The Northern Chinese breeds were most similar to the European breeds. Although some overlap exists, Chinese breeds showed a higher average degree of heterozygosity and genetic distance compared to European ones. Between breed diversity was even more pronounced and was the highest in the Central Chinese pigs, reflecting the geographically central position in China. Comparing correlations between genetic distance and heterozygosity revealed that China and Europe represent different domestication or breed formation processes. A likely cause is a more diverse wild boar population in Asia, but various other possible contributing factors are discussed.
    Effects of inbreeding on survival, body weight and fluctuating asymmetry (FA) in Nile tilapia, Oreochromis niloticus
    Fessehaye, Y. ; Komen, J. ; Rezk, M.A. ; Arendonk, J.A.M. van; Bovenhuis, H. - \ 2007
    Aquaculture 264 (2007). - ISSN 0044-8486 - p. 27 - 35.
    trout salmo-gairdneri - rainbow-trout - developmental stability - oncorhynchus-mykiss - depression - traits - heterozygosity - growth - populations - fitness
    The present study investigated the effects of different levels of inbreeding on survival, growth, body weight and fluctuating asymmetry (FA) in O. niloticus. We mated 20 sires and 35 dams in a full-sib/half-sib mating design to produce 35 full-sib families with expected level of inbreeding (F%.) of 0.0, 6.3, 9.4, 12.5 and 25. Fry were produced and reared in hapas suspended in fertilized ponds until time of tagging. In total 1832 fish were tagged with Floy (R) tags and stocked in two fertilized earthen ponds. During the experiment fish were not fed but relied entirely on natural food available in the ponds. Fish were harvested after a period of 8 months, which included 3 months of over-wintering. Results show that level of inbreeding significantly affected early fry survival and body weight at stocking. Level of inbreeding did not affect survival and body weight at harvest. Pond, weight at stocking, sire and dam had significant effects on body weight and pond survival at harvest. FA was not significantly affected by the level of inbreeding or sire. However, FA was significantly affected by dam (which constitutes the combined effects of hapa rearing, age of fish and maternal (genetic) effects), and pond. This suggests that FA is more influenced by environmental than by genetic factors in the population of Nile tilapia studied. The observed difference in effects of inbreeding on early and later life stages can be explained by strong natural selection on fitness during over-wintering. (c) 2007 Elsevier B.V. All rights reserved.
    Possible negative effects of inbreeding on semen quality in Shetland pony stallions
    Eldik, P. van; Waaij, E.H. van der; Ducro, B.J. ; Kooper, A.W. ; Stout, T.A.E. ; Colenbrander, B. - \ 2006
    Theriogenology 65 (2006)6. - ISSN 0093-691X - p. 1159 - 1170.
    reproductive-performance - fluctuating asymmetry - ejaculate quality - fertility - heterozygosity - populations - depression - parameters - season - sperm
    Inbreeding is widely believed to negatively affect reproductive performance. Indeed, in some species, high levels of inbreeding are thought to be the major cause of poor semen quality. It is, however, not clear whether inbreeding affects fertility in horses. In this study, the relationship between inbreeding and semen quality was examined in 285 immature Shetland pony stallions submitted for breeding soundness examination in March-April of the years 1992-1997. The majority of stallions examined were 3 years old (85%) and their coefficients of inbreeding ranged from 0 to 25% (mean ± S.D.: 3 ± 4.6%). For the purpose of analysis, stallions were divided into six inbreeding classes (0-1, 1-2, 2-5, 5-8, 8-12 and >12%) containing 132, 40, 42, 27, 25 and 19 animals, respectively. The degree of inbreeding significantly affected many aspects of sperm production and quality, based on a standard examination of two ejaculates collected at a 1.5-3 h interval. In particular, coefficients of inbreeding above 2% were associated with lower percentages of motile (p <0.01) and morphologically normal sperm (p <0.001). When the data set was used to estimate heritability of semen characteristics, the high values calculated for sperm progressive motility (0.46) and concentration (0.24) suggested that these traits could be improved by phenotypic selection. These findings support the hypothesis that inbreeding has a detrimental effect on semen quality in Shetland ponies, although examination of multiple ejaculates after repeated semen collection to bring the animals to daily sperm output is needed to confirm this conclusion. Nevertheless, the results support previous suggestions that inbreeding is an important cause of reduced semen quality
    Genetic diversity in European pigs utilizing amplified fragment lenght polymorphism markers. AFLP markers
    SanCristobal, M. ; Chevalet, C. ; Peleman, J. ; Heuven, H.C.M. ; Brugmans, B.W. ; Schriek, M. van; Joosten, R. ; Rattink, A.P. ; Harlizius, B. ; Groenen, M.A.M. ; Amigues, Y. ; Boscher, M.Y. ; Russell, G. ; Law, A. ; Davoli, R. ; Russo, V. ; Desautes, C. ; Alderson, L. ; Fimland, E. ; Bagga, M. ; Delgado, J.V. ; Vega-Pla, J.L. ; Marinez, A.M. ; Ramos, M. ; Glodek, P. ; Meyer, J.N. ; Gandini, G.C. - \ 2006
    Animal Genetics 37 (2006)3. - ISSN 0268-9146 - p. 232 - 238.
    dierveredeling - varkens - varkensrassen - conservering - dna - allelen - genetische afstand - genetische diversiteit - genetische merkers - genotypen - heterozygotie - microsatellieten - wiskundige modellen - meishan - aflp - animal breeding - pigs - pig breeds - conservation - dna - alleles - genetic distance - genetic diversity - genetic markers - genotypes - heterozygosity - microsatellites - mathematical models - meishan - amplified fragment length polymorphism - population diversity - distance - trees - aflp
    The use of DNA markers to evaluate genetic diversity is an important component of the management of animal genetic resources. The Food and Agriculture Organisation of the United Nations (FAO) has published a list of recommended microsatellite markers for such studies; however, other markers are potential alternatives. This paper describes results obtained with a set of amplified fragment length polymorphism (AFLP) markers as part of a genetic diversity study of European pig breeds that also utilized microsatellite markers. Data from 148 AFLP markers genotyped across samples from 58 European and one Chinese breed were analysed. The results were compared with previous analyses of data from 50 microsatellite markers genotyped on the same animals. The AFLP markers had an average within-breed heterozygosity of 0.124 but there was wide variation, with individual markers being monomorphic in 3¿98% of the populations. The biallelic and dominant nature of AFLP markers creates a challenge for their use in genetic diversity studies as each individual marker contains limited information and AFLPs only provide indirect estimates of the allelic frequencies that are needed to estimate genetic distances. Nonetheless, AFLP marker-based characterization of genetic distances was consistent with expectations based on breed and regional distributions and produced a similar pattern to that obtained with microsatellites. Thus, data from AFLP markers can be combined with microsatellite data for measuring genetic diversity.
    Genetic diversity within and between European pig breeds using microsatellite markers
    SanCristobal, M. ; Chevalet, C. ; Haley, C.S. ; Joosten, R. ; Rattink, A.P. ; Harlizius, B. ; Groenen, M.A.M. - \ 2006
    Animal Genetics 37 (2006)3. - ISSN 0268-9146 - p. 189 - 198.
    dierveredeling - varkens - wilde varkens - varkensrassen - conservering - rasverschillen - biodiversiteit - genetische afstand - genetische diversiteit - genetische merkers - heterozygotie - allelen - microsatellieten - populatiegenetica - statistische analyse - animal breeding - pigs - wild pigs - pig breeds - conservation - breed differences - biodiversity - genetic distance - genetic diversity - genetic markers - heterozygosity - alleles - microsatellites - population genetics - statistical analysis - populations - evolution - humans - loci - distance
    An important prerequisite for a conservation programme is a comprehensive description of genetic diversity. The aim of this study was to use anonymous genetic markers to assess the between- and the within-population components of genetic diversity for European pig breeds at the scale of the whole continent using microsatellites. Fifty-eight European pig breeds and lines were analysed including local breeds, national varieties of international breeds and commercial lines. A sample of the Chinese Meishan breed was also included. Eleven additional breeds from a previous project were added for some analyses. Approximately 50 individuals per breed were genotyped for a maximum of 50 microsatellite loci. Substantial within-breed variability was observed, with the average expected heterozygosity and observed number of alleles per locus being 0.56 [range 0.43–0.68] and 4.5 respectively. Genotypic frequencies departed from Hardy–Weinberg expectations (P <0.01) in 15 European populations, with an excess of homozygotes in 12 of them. The European breeds were on average genetically very distinct, with a Wright FST index value of 0.21. The Neighbour-Joining tree drawn from the Reynolds distances among the breeds showed that the national varieties of major breeds and the commercial lines were mostly clustered around their breeds of reference (Duroc, Hampshire, Landrace, Large White and Piétrain). In contrast, local breeds, with the exception of the Iberian breeds, exhibited a star-like topology. The results are discussed in the light of various forces, which may have driven the recent evolution of European pig breeds. This study has consequences for the interpretation of biodiversity results and will be of importance for future conservation programmes.
    Biodiversity of 52 chicken populations assessed by microsatellite typing of DNA pools
    Hillel, J. ; Groenen, M.A.M. ; Tixier-Boichard, M. ; Korol, A.B. ; David, L. ; Kirzhner, V.M. ; Burke, T. ; Barre-Dirie, A. ; Crooijmans, R.P.M.A. ; Elo, K. ; Fieldman, M.W. ; Freidlin, P.J. ; Maki-Tanila, A. ; Oortwijn, M.E.P. - \ 2003
    Genetics, Selection, Evolution 35 (2003)5. - ISSN 0999-193X - p. 533 - 557.
    genetic-distance - linkage map - markers - origin - breeds - lines - heterozygosity - fingerprints - diversity - samples
    In a project on the biodiversity of chickens funded by the European Commission (EC), eight laboratories collaborated to assess the genetic variation within and between 52 populations from a wide range of chicken types. Twenty-two di-nucleotide microsatellite markers were used to genotype DNA pools of 50 birds from each population. The polymorphism measures for the average, the least polymorphic population ( inbred C line) and the most polymorphic population (Gallus gallus spadiceus) were, respectively, as follows: number of alleles per locus, per population: 3.5, 1.3 and 5.2; average gene diversity across markers: 0.47, 0.05 and 0.64; and proportion of polymorphic markers: 0.91, 0.25 and 1.0. These were in good agreement with the breeding history of the populations. For instance, unselected populations were found to be more polymorphic than selected breeds such as layers. Thus DNA pools are effective in the preliminary assessment of genetic variation of populations and markers. Mean genetic distance indicates the extent to which a given population shares its genetic diversity with that of the whole tested gene pool and is a useful criterion for conservation of diversity. The distribution of population-specific (private) alleles and the amount of genetic variation shared among populations supports the hypothesis that the red jungle fowl is the main progenitor of the domesticated chicken.
    A meiotic study of two translocations and a tertiary trisomic in the mouse (Mus musculus)
    Boer, P. de - \ 1975
    Landbouwhogeschool Wageningen. Promotor(en): J. Sybenga. - Wageningen : [s.n.] - 79
    heterozygotie - genetische variatie - overerving - muizen - muridae - meiose - trisomie - heterozygosity - genetic variation - inheritance - mice - muridae - meiosis - trisomy
    In this section, the order of the articles has not been closely followed. Each point ends with the number(s) of the article(s) (as given in the contents), where the conclusion is based on.

    1) Cytological meiotic studies of T(2;8)26H and T(1;13)70H heterozygotes and Ts(1 13)70H tertiary trisomics indicate, that chiasmata are more often located in the distal (translocated) segments than in the proximal (interstitial) segments containing centric heterochromatin (3 and 5).

    2) This study opens the possibility that the presence of centric heterochromatin decreases the probability of chiasma formation in its vicinity with a positive gradient distally (5).

    3) The genetic lengths of the interstitial and translocated chromosome segments coincide rather well with the physical length of these segments as estimated with the aid of Giemsa-banding. This finding does not fit the tendency expressed in the conclusions 1 and 2. The apparent exception of this rule is segment 13 t which is overestimated when looking at genetic recombination. For cytological studies, the physical length of a segment is of a greater value (4).

    4) Univalence for chromosome 1 13at metaphase I - anaphase I does not lead to an appreciable loss of this chromosome in the male, neither in the Ts(1 13)70H tertiary trisomic karyotype nor in the T(1;13)70H heterozygote (3 and 5).

    5) In the T70H/+ karyotype, there is strong evidence for coorientation of the 1 13univalent so that the four reciprocal translocation involved chromosomes segregate two by two. Occasionally, equational separation of the two 1 13chromatids may occur at anaphase I (5).

    6) The segregational behavior of heterozygous translocation multivalent configurations can, within the genetic background concerned, be best explained by time differences of chiasma terminalization during metaphase I - anaphase 1 (5).

    7) The genetic background most likely exerts an influence on the behavior of mouse reciprocal translocations (5).

    8) The reliability of the formula which relates the summed frequencies of adjacent II disjunction and numerical non- disjunction and the relative viability of heterozygous translocation outcross progeny depends on the existence of selection against small litters during gestation. This is the more likely when the theoretically expected litter size decreases (5).

    9) A-chiasmate non-homologous chromosome association of the centric heterochromatin of chromosome 1 13and the X-chromosome does occur (3 and 5).

    10) The majority of male Ts(1 13)70H tertiary trisomics are capable of producing offspring. Thus, tertiary trisomy does not invariably lead to sterility in the male mouse (2 and 3).

    11) Tertiary trisomics for chromosome 1 13in the mouse display a variety of phenotypes. The condition can lead to death in utero, to death before weaning, to morphologically affected but viable animals and to animals with an unaltered appearance (2 and 3).

    12) The ratio between morphologically affected and unaffected tertiary trisomics for chromosome 1 13at birth (live or dead) amounts to between 2 and 3. This ratio might depend on the genetic background concerned (2 and 3).

    13) The most obvious abnormality of the morphologically affected tertiary trisomics of the Ts(1 13)70H karyotype is a malformation of the bones of the skull which often leads to an abnormal growth of the upper and lower incisors (2).

    14) The impaired fertility of Ts(1 13)70H males is most probably due to a lowered production of functional spermatozoa and the consequences this has for the continuation of pregnancy. Thus, the elimination of "unbalanced" progeny is not the first cause (3).

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