Geographic variation of sex-linked translocation heterozygosity in the termite Kalotermes approximatus snyder (Insecta: Isoptera)

The primitive termite Kalotermes approximatus carries a number of reciprocal translocations (segmental interchanges) that are linked to the sex-determining mechanism in such a way that males are permanent structural heterozygotes, forming long chains or rings of chromosomes in meiosis, while females are structural homozygotes, forming only bivalents. A survey of male meiosis from collections covering nearly the whole species range in the southeastern United States reveals considerable variation in the number of translocations: males with a diploid number of 32 or 33 have meiotic chains of 11, 13, 14, 15, 16, and 17 or 19 chromosomes. The different types can be arranged in an evolutionary series of rearrangements involving translocations or Robertsonian fusions between chromosomal elements in the ring and those outside. In addition, the existence of a closed chain (ring) of 16, and of four different types of chain of 13, indicate that similar rearrangements have occurred among chain elements. The geographic pattern of these rearrangements suggests that their selection accompanied the expansion of the species northward from southern Florida sometime since the last glaciation or, alternatively, that as they arose the new translocation types successively supplanted the ancestral types, preferentially in the east-central portion of the range.     

Postmating reproductive isolation and modification of the ‘sex ratio’ trait inDrosophila subobscura induced by the sex chromosome gene arrangement A2+3+5+7

Drosophila subobscura males were trapped in Tunis, and mated to different lab strains. The offspring from 15% of these wild Tunisian males consisted of more than 90% females. Chromosome analysis showed that these males had carried the A2+3+5+7 which was described as 'sex ratio' chromosome, endemic in North Africa and the Canary Islands. The mean female frequency in the total offspring of all trapped males was 61%. This percentage was stable for more than ten years. F1 females from the mating of wild Tunisian males to Küsnacht standard females were backcrossed to Küsnacht standard males. In the offspring of this back cross, A2+3+5+7-males were sterile. The fertility of A2+3+5+7-males could be restored in two ways: 1) When the Küsnacht standard autosomes were replaced by Tunisian autosomes, most of the A2+3+5+7-males were again fertile. The A2+3+5+7-chromosome seems to be incompatible with autosomes from a geographically distant region. 2) After exchanging autosomes between lines, in which A2+3+5+7-males were 100% sterile, fertility could be restored in 30% of the A2+3+5+7-males. All males carrying one specific A2+3+5+7 stayed sterile as well in combination with autosomes from different lines as with Tunisian autosomes. The Y-chromosome and the cytoplasm was the same in sterile and in fertile A2+3+5+7-males. Therefore the origin of the Y-chromosome and the cytoplasm could not play a major role in sterility. The percentage of fertile males varied for different Y-chromosomes. Thus the Y-chromosomes may have some influence on fertility in this study. The restored fertility of A2+3+5+7-males can be explained assuming complementation. Defects of autosomes, and perhaps of the Y-chromosomes, could differ from line to line. Genomic changes may have happened when the A2+3+5+7 was in the genome together with autosomes and Y-chromosomes from Swiss populations. The A-chromosome which prevented fertility in all combinations, is thought to be itself defective. In one cross the 'sex ratio' trait was modified. In the offspring of some males the male to female ratio was 1:1. The variable sex ratio in the offspring from different males may have been an effect of the autosomes. In short, the intraspecific hybrid sterility and modification of the 'sex ratio' trait in D. subobscura indicate that: a) an incompatibility possibly existed between the gene arrangement A2+3+5+7 from one population and autosomes respectively Y-chromosomes from a population isolated from the former. b) In addition unidentified genomic changes occurred, c) induced by the A2+3+5+7-chromosome. d) The sex chromosomes A and Y, and the autosomes were involved.     

Skewed distribution of morphological character scores and molecular markers in three interspecific crosses in Rosa section Caninae

The dogroses, Rosa section Caninae, are all polyploid and characterised by their unbalanced meiosis; the pollen parent contributes one genome, whereas the seed parent contributes 3-5 genomes depending upon ploidy level of the species. As a result, genetically determined traits are expected to be matroclinally inherited. In the present study, the transmittal of genetic material was studied using manually scored reproductive characters (ovary and sepals), automated image analysis of leaflet shape (Fourier coefficients), and molecular markers (RAPD). The plant material consisted of a pair of reciprocal crosses between R. sherardii and R. villosa, a R. rubiginosa x R. sherardii cross and offspring obtained from selfing or within-population crosses of the parental species. All but one of the maternal markers were transmitted to all the offspring plants, whereas only 41% of the paternal markers were transmitted to all of them, 23% were never transmitted and 36% reached only one or two of the offspring plants. Canonical variates analyses (CVA) based on the vegetative characters could easily separate the offspring groups representing parental species and also all three hybridogenous offspring groups from each other, whereas CVA based on reproductive characters failed to separate R. sherardii x R. villosa from its seed parent, but otherwise distinguished all offspring groups. The study shows that the expression of characters as well as molecular marker inheritance is dependent upon the direction of the cross, and on the species involved. It also demonstrates the importance of employing several different types of character sets for an improved comprehension of the effects of the peculiar canina meiosis.     

Meiotic disjunction and embryonic lethality in trisomies derived from an X-linked translocation in the onion fly,Hylemya antiqua (Meigen)

Translocation- and tertiary trisomies (for the X-chromosomes) were obtained after testcrossing translocation heterozygous females of an X-linked “simple” translocation stock. Meiotic disjunction as judged from segregations at M II (males) and in young eggs of testcrosses (males and females) in translocation trisomics was studied. No progeny of tertiary trisomic males and females was found, but male M II could be studied. Six different orientation types appeared in translocation trisomie (2n + 1) males and these were present in equal frequencies. No adjacent II configurations were found. The small X- and Y-chromosomes and the large translocated X-chromosome of the translocation complex disjoin at random (n and n + 1 gametes) in both translocation- and tertiary trisomic males. In translocation trisomic females four different orientation types appeared. From the high frequency of two of these (together, 94.5%) it is concluded that the two normal X-chromosomes show preferential pairing and disjunction, while the translocated X-chromosome moves to either one of the two poles at random. Primary trisomic (for the X-chromosome) males (XXY) and females (XXX) were obtained from testerossed translocation trisomics. Cytological analysis of adult male progeny of testerossed XXY males showed that no random orientation for the X-, X- and Y-chromosomes occurred because half of the sons was disomic (XY) and half of them trisomic (XXY). A possible mechanism is discussed. Analysis of young eggs of testerossed XXX females indicated a segregation of 2X∶1X=1∶1. The level of “semi”-sterility as scored from testcrosses of translocation trisomies appeared to be as in translocation heterozygotes. Here again a close relation exists between “semi”-sterility and deficiencies in eggs for a large chromosomal segment. The possible use of this translocation for genetic control of insect pests is discussed.     

X-ray induction of autosomal translocations in spermatozoa of Drosophila melanogaster and maternal effects of X.Y-chromosomes.

Wild-type ORK Drosophila melanogaster males were given an exposure of 3000 R X-radiation. Mature sperm were then sampled by mating to X.Y/X.Y, X.Y/X, or X/X females that carried markers on the second and third chromosomes for the detection of induced autosomal translocations. Two pairs of maternal stocks were used and heterozygous X.Y/X females were obtained by making both reciprocal crosses. The highest frequencies of induced translocations were obtained with X/X females. In one series these frequencies are higher than those obtained with either X.Y/X or X.Y/X.Y females. In the other series a uniform frequency of translocations was obtained with all types of female, except for one of the two types of heterozygous female, which gave lower frequencies. The experiments have provided data which show that the addition of Y-chromosomes to the maternal genome does not have a specific effect on the recovery of induced paternal autosomal translocations. Maternal Y-chromosomes increased the proportions of fertile F1 males, this effect being consistent in direction but varying in degree.     

Kinda baboons (Papio kindae) and grayfoot chacma baboons (P. ursinus griseipes) hybridize in the Kafue river valley, Zambia

The ranges of small kinda (Papio kindae) and much larger grayfooted chacma (P. ursinus griseipes) baboons adjoin in the Kafue National Park, Zambia. In a visual survey of baboons at 48 sites in the Kafue River drainage we found that, contrary to previous reports, groups at the species interface near the town of Ngoma are phenotypically diverse and presumably formed by multigenerational hybridization. Mitochondrial and/or Y-chromosome genetic markers from fecal samples (N=164) collected at 29 sites support this conclusion. Groups with phenotypic signs of a history of hybridization also had taxon-specific mitochondria and Y-haplotypes from both parental species. Although the distribution of mitochondrial haplotypes largely mirrored that of external phenotypes, a significant proportion of male specimens from grayfoot as well as hybrid groups carried kinda Y-chromosomes, and kinda Y-chromosomes were involved in all observed cases of mitochondrial/Y-chromosome discordance. These observations are consistent with, though they do not prove, a population history in which the range of chacmas and the hybrid zone have advanced at the expense of the kinda range. They also suggest that, unexpectedly, kinda male×chacma female matings are much more common than the reciprocal cross in the ancestry of hybrids. We suggest that distinctive male kinda behavior and the "juvenile" appearance of kinda baboons of both sexes, perhaps combined with obstetric difficulties of a small kinda female carrying the large offspring of a chacma male, may account for this bias.     

Differential sexual survival of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> on copper sulfate

Based on studies of the influence of X-chromosomes on the viability of Drosophila melanogaster exposed to cadmium, and on the role of X-linked genes on copper homeostasis, we examined the effect of copper sulfate (CuSO₄) on offspring viability using three independent, inbred D. melanogaster crosses (ensuring identical autosomes for males and females within each cross). Each cross was performed with attached X-chromosome females and males with a single X-chromosome. As female D. melanogaster have less metallothionein RNA expression than males, we predicted fewer female offspring than male offspring in crosses exposed to CuSO₄, even though females have two copies of X-chromosome genes, possibly resulting in overdominant heterozygosity. In two of three crosses, CuSO₄ caused significantly higher numbers of male offspring compared to female offspring. We hypothesized that these gender-based viability differences to copper exposure are caused by X-chromosome ploidy and X-linked genetic variation affecting metallothionein expression. Observed differential offspring viability responses among crosses to copper exposure also showed that different genetic backgrounds (autosomal and/or X-chromosome) can result in significant differences in heavy metal and metallothionein regulation. These results suggest that the effect of copper on offspring viability depends on both genetic background and gender, as both factors can affect the regulation of metallothionein proteins as well as homeostasis of biologically necessary heavy metals.     

No induction of interchromosomal effect in male meiosis of Chinese hamsters with reciprocal translocations

Chinese hamsters from five strains with reciprocal translocations, T(1;3)7Idr, T(1;3)8Idr, T(1;2)9Idr, T(7;9)16Idr, and T(1;5)17Idr, and a karyotypically normal strain, CHS/Idr, were used to look for an interchromosomal effect by chromosomal analysis of meiotic cells and one-cell embryos. The frequencies of nondisjunction at first meiosis in five normal (+/+) males, calculated by doubling the number of hyperhaploid cells, ranged from 0.43% to 1.33%, and there was no significant difference in frequency among individuals. On the other hand, the frequency of hyperhaploid cells in males heterozygous for each translocation ranged from 3.0% to 11.8%, and the frequency of hyperhaploid cells with an extra translocation-unrelated chromosome ranged from 0.2% to 0.4%, which is no different from that estimated from scoring of +/+ males at the second meiotic metaphase. In one-cell embryos from crosses between karyotypically normal females and male heterozygotes for T(1;2)9Idr and T(7;9)16Idr, 1.1% and 0.5% of embryos had an extra translocation-unrelated chromosome. Compared with the control, the frequency of meiotic nondisjunction showed no increase in male heterozygotes for the reciprocal translocations. Therefore, the results suggest that multivalents and rearranged chromosomes existing at first and second meiosis in male Chinese hamsters exert no influence on segregation of normal bivalents and chromosomes unrelated to the rearrangements.     

Evaluation of genetic damage induced by 8-ethoxycaffeine in Drosophila melanogaster

The methylated oxypurine, 8-ethoxycaffeine (EOC), was tested for the induction of genetic damage in Drosophila melanogaster. Sex-linked recessive lethals, sex-chromosome loss and tanslocation induction were studied following treatment of adult males, using a feeding technique. Our results show that EOC induces sex-chromosome loss and translocations between the second and third chromosomes, but is unable to induce point mutations in male germ cells under our conditions of testing.     

Strong biases in the transmission of sex chromosomes in the aphid Rhopalosiphum padi

The typical life cycle of aphids involves several parthenogenetic generations followed by a single sexual one in autumn, i.e. cyclical parthenogenesis. Sexual females are genetically identical to their parthenogenetic mothers and carry two sex chromosomes (XX). Male production involves the elimination of one sex chromosome (to produce X0) that could give rise to genetic conflicts between X-chromosomes. In addition, deleterious recessive mutations could accumulate on sex chromosomes during the parthenogenetic phase and affect males differentially depending on the X-chromosome they inherit. Genetic conflicts and deleterious mutations thus may induce transmission bias that could be exaggerated in males. Here, the transmission of X-chromosomes has been studied in the laboratory in two cyclically parthenogenetic lineages of the bird cherry-oat aphid Rhopalosiphum padi . X-chromosome transmission was followed, using X-linked microsatellite loci, at male production in the two lineages and in their hybrids deriving from reciprocal crosses. Genetic analyses revealed non-Mendelian inheritance of X-chromosomes in both parental and hybrid lineages at different steps of male function. Putative mechanisms and evolutionary consequences of non-Mendelian transmission of X-chromosomes to males are discussed.     

Tertiary trisomics in pearl millet (Pennisetum typhoides Stapf & Hubb)

Four tertiary trisomic plants are reported here, two of them (Nos. Tr11 and Tr13) from selfed progeny of a triploid Pearl millet and the other two (Nos. 3/12 and 16/7) from the progenies of radiation induced interchange heterozygotes. The extra chromosome in Tr13 and 3/12 was the nucleolus organizing chromosome. In No. 16/7 an extra chromosome enters into an association chromosomes were also involved. Meiotic behaviour in these four trisomics indicates that Tr11 and 3/12 are tertiary trisomics. It is suggested that two reciprocal translocations have occurred between two sets of chromosomes in the triploid parent and that syngamy has taken place in such a way that four interchange chromosomes and one non-interchange nucleolus organizing chromosome have come together in the offspring. The extra chromosome in No. 16/7 is an interchange chromosome which is homologous to one of the chromosomes of an interchange complex of six chromosomes.     

Radiation-induced inversions and reciprocal translocations in Anopheles atroparvus

Inversions and reciprocal translocations were induced in Anopheles atroparvus by irradiation of males with X-rays. 22 aberrations were produced in stocks and were identified as follows: 6 paracentric, 6 pericentric inversions and 10 reciprocal translocations (9 autosomal and 1 sex-linked). Partial sterility in the offspring of this stock is demonstrated. The practical significance of constructing stocks with inversions and translocations for genetic control of pest insects is considered.     

Chiasma distributions and chromosome segregation in male and female translocation heterozygous mice analysed using FISH

Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a translocation [T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations. However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata, also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice. The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was not the case for T(7;16)67H. Received: 6 June 1998 / Accepted: 9 October 1998     

The induction by X-rays of chromosome aberrations in male guinea-pigs, golden hamsters and rabbits. II. Properties of translocations induced in post-meiotic stages.

Translocations induced by X-rays in post-meiotic germ cells of male guinea-pigs, golden hamsters and rabbits were studied cytologically in the F1 sons of the irradiated males. The percentage of spermatocytes displaying multivalent configurations varied with the translocation, but the average percentage appeared to depend on the species: fewer quadrivalents were observed in hamster than in guinea-pig heterozygotes and most were recorded for rabbit heterozygotes. Chain quadrivalents were more abundant than ring quadrivalents at meiosis for the guinea-pig and hamster, in contrast to the mouse. Too few translocation heterozygotes were examined to determine which meiotic configuration was the more prevalent in the rabbit. In all three species, as in the mouse, translocations were found which caused male sterility, due to partial or complete failure of spermatogenesis, although most translocations caused semi-sterility. For these semi-sterile males both the frequency and time of embryonic death in the progeny appeared to be the same as in the mouse. It is concluded that similar types of chromosome aberrations are induced by X-rays in post-meiotic germ cells of male guinea-pigs, rabbits, golden hamsters and mice.     

Testing the viviparity-driven-conflict hypothesis: parent-offspring conflict and the evolution of reproductive isolation in a poeciliid fish

The evolution of viviparity increases the potential for genomic conflicts between mothers and offspring over the level of maternal investment. The viviparity-driven-conflict hypothesis predicts that such conflicts will drive the evolution of asymmetrical reproductive isolation between populations with divergent mating systems. We tested this hypothesis using crosses between populations of a poeciliid fish that differ in their level of polyandry. Our results support the prediction of an asymmetry in the rate of spontaneous abortion in reciprocal crosses, with the highest rate occurring in crosses between females from a relatively monandrous population and males from a relatively polyandrous population. The patterns of offspring size were not consistent with the pattern predicted by the viviparity-driven-conflict hypothesis: crosses between a monandrous female and a polyandrous male did not produce larger offspring than the reciprocal cross. This discrepancy was due to the presence of an effect of the maternal population on offspring size: polyandrous females produced larger offspring than monandrous females. In addition, offspring size was positively correlated with maternal size in crosses involving a polyandrous male. We discuss these results in light of models for intra- and intergenomic epistasis and the rapid origin of asymmetric reproductive isolation in viviparous taxa.     

Hyperthermia of male Drosophila melanogaster meiocytes induces abnormalities in both paternal and maternal sex chromosome sets of the offspring

Nondisjunction and loss of sex chromosomes caused by exposure of male Drosophila melanogaster to heat shock (HS) (37 degrees C for 1 h) has been studied to determine the role of mutation l(1)ts403 (sbr10) in the control of chromosome segregation during cell division. Hyperthermia of males at the pupal stage has been demonstrated to increase the number of offspring with abnormalities of not only paternal, but also maternal sex chromosome sets. According to the criterion used, there is a temperature-sensitive period of spermatogenesis, which presumably coincides with meiosis. Phenotypes of some individuals correspond to the presence of two sex chromosomes of obtained from the same parent. The frequency of abnormal chromosome sets in the offspring of male carriers of the sbr10 mutation is about two times higher than in the offspring of males without this mutation.     

Non-reciprocal cross-incompatibility in Trichogramma deion

In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility.     

Four familial translocations ascertained through spontaneous abortions

Summary In a study of 514 spontaneous abortions, 194 were found to have a chromosome anomaly. Of these, 4 (2.1%) were unbalanced translocations. Three of the translocations were Robertsonian (13q14q) and one was reciprocal. Each translocation was ascertained independently and each was associated with a balanced rearrangement in a carrier parent.