Geographic variability in expression of the sex-linked AAT-1 gene of the bell-ring frog, Buergeria buergeri

Cytological observation and artificial crossing experiments were used to examine the geographic differences in the sex-determining mechanism and mode of inheritance of the sex-linked AAT-1 gene in the bell-ring frog, Buergeria buergeri. The AAT-1 phenotypes were also examined by allozyme analysis using field-caught females and males collected from 19 populations from the Honshu, Shikoku, and Kyushu islands of Japan, in order to comprehensively elucidate the geographic variability in the expression of the sex-linked AAT-1 gene of B. buergeri. The results showed that the Aomori population of B. buergeri from the northern end of Honshu was female heterogametic in sex determination, that chromosome No. VII was a sex chromosome of the ZZ/ZW type, and that the sex-linked AAT-1 gene was expressed on both the Z and W chromosomes. This mode of AAT-1 expression in the Aomori population was different from that in the Hiroshima population from western Honshu, in which the AAT-1 gene was expressed on the Z chromosome but not on the W chromosome. The results also showed that there was no differentiation among populations in the expression of the AAT-1 genes on the Z chromosome, whereas two populations, the Hiroshima and Aomori frogs, exhibited distinct modes of expression of the AAT-1 gene on the W chromosome. These two modes of expression may be widely distributed in western and eastern Japan, and coexist in the central part of Honshu.     

Triploid plover female provides support for a role of the W chromosome in avian sex determination

Two models, Z Dosage and Dominant W, have been proposed to explain sex determination in birds, in which males are characterized by the presence of two Z chromosomes, and females are hemizygous with a Z and a W chromosome. According to the Z Dosage model, high dosage of a Z-linked gene triggers male development, whereas the Dominant W model postulates that a still unknown W-linked gene triggers female development. Using 33 polymorphic microsatellite markers, we describe a female triploid Kentish plover Charadrius alexandrinus identified by characteristic triallelic genotypes at 14 autosomal markers that produced viable diploid offspring. Chromatogram analysis showed that the sex chromosome composition of this female was ZZW. Together with two previously described ZZW female birds, our results suggest a prominent role for a female determining gene on the W chromosome. These results imply that avian sex determination is more dynamic and complex than currently envisioned.     

Evidence for two successive pericentric inversions in sex lampbrush chromosomes of Rana rugosa (Anura: Ranidae)

The objective of this study was to clarify the course of inversions by which a ZW sex chromosome dimorphism has become established in Rana rugosa. Fortunately, R. rugosa preserves three different forms of sex chromosomes in the several isolated populations. In both males and females, the homomorphic sex chromosomes from Hiroshima were closely similar to Z, while those from Isehara were slightly different from the Z. Females from Hirosaki demonstrated heteromorphic sex chromosomes. In this study, the configuration and pairing behavior of sex lampbrush chromosomes were examined in the female offspring produced from a cross between a female from Hiroshima and a male from Isehara, as well as the female offspring of a female from Hirosaki and the male from Isehara. For the sex lampbrush chromosomes from Hiroshima and Isehara, chiasmata were exclusively formed between the distal regions of the long arms of one sex chromosome and the terminal regions of the short arms of the other. As a result, landmarks arranged in reverse order were observed in the achiasmatic regions of these chromosomes. For the sex lampbrush chromosomes from Isehara and Hirosaki, on the other hand, chiasma formation was mainly confined to the lower half of the chromosomes corresponding to the long arms, and the landmarks in the achiasmatic regions of these chromosomes were disposed in the opposite direction to each other. These results seem to indicate that in the primitive sex chromosomes of the Hiroshima type two pericentric inversions occurred, leading to the differentiation of the W chromosomes. This is the first report to substantiate the process of sex chromosome differentiation experimentally. Received: 10 November 1996; in revised form: 22 April 1997 / Accepted: 24 April 1997     

The genetic defect in multiple endocrine neoplasia type 2A maps next to the centromere of chromosome 10

Multiple endocrine neoplasia type 2A (MEN2A) is a rare cancer syndrome that is inherited in an apparently autosomal dominant fashion. Previous linkage studies had assigned the MEN2A locus to chromosome 10 in the pericentromeric region. We recently have described several new easily scorable RFLPs for the chromosome 10-specific alpha satellite DNA (the D10Z1) locus that is known, on the basis of previous in situ hybridization experiments, to lie at the centromere. We report here tight linkage between MEN2A and D10Z1, as demonstrated by a maximum lod score of 12.02 at the recombination frequency of zero (1-lod-unit support interval 0-4 cM), indicating that the genetic defect in MEN2A lies in the immediate vicinity of the centromere. By means of a set of ordered polymorphic DNA markers from the pericentromeric region, multipoint as well as pairwise linkage analyses place the MEN2A locus at the middle of a small region (approximately 11 cM) bracketing the centromere with FNRB (at 10p11.2) and RBP3 (at 10q11.2) on either side, providing further support for the centromeric location of the MEN2A locus. Marked sex difference in recombination frequencies exists in this pericentromeric region: significantly (P less than .01) more female than male crossovers were observed across all of the adjacent intervals D10S24-FNRB, FNRB-D10Z1, and D10Z1-RBP3. However, a sex difference was not seen in the 7-cM interval from RBP3 to D10S5, suggesting that large variation in the sex difference in recombination can occur over small chromosomal regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Z LINKAGE OF FEMALE PROMISCUITY GENES IN THE MOTH UTETHEISA ORNATRIX: SUPPORT FOR THE SEXY‐SPERM HYPOTHESIS?

Female preference genes for large males in the highly promiscuous moth Utetheisa ornatrix (Lepidoptera: Arctiidae) have previously been shown to be mostly Z‐linked, in accordance with the hypothesis that ZZ–ZW sex chromosome systems should facilitate Fisherian sexual selection. We determined the heritability of both female and male promiscuity in the highly promiscuous moth U. ornatrix (Lepidoptera: Arctiidae) through parent–offspring and grandparent–offspring regression analyses. Our data show that male promiscuity is not sex‐limited and either autosomal or sex‐linked whereas female promiscuity is primarily determined by sex‐limited, Z‐linked genes. These data are consistent with the “sexy‐sperm hypothesis,” which posits that multiple‐mating and sperm competitiveness coevolve through a Fisherian‐like process in which female promiscuity is a kind of mate choice in which sperm‐competitiveness is the trait favored in males. Such a Fisherian process should also be more potent when female preferences are Z‐linked and sex‐limited than when autosomal or not limited.     

Confirmation of avian sex-chromosome linkage of liver cytosolic aconitase (ACO1)

Frequencies of liver cytosolic aconitase (ACO1) allozyme phenotypes in female zebra finches (Poephila guttata) conformed to a sex-chromosome-linked model of inheritance. Since birds are characterized by female heterogamety (ZZ males, ZW females), the observed absence of female heterozygotes for the cytosolic aconitase gene is interpreted as suggesting linkage of the ACO1 locus to the Z chromosome and hemizygous expression of this locus. Confirmation of this linkage assignment provides further support for the concept of evolutionary conservation of the avian Z chromosome.     

Male-offspring-specific, haplotype-dependent, nonrandom cosegregation of alleles at loci on two mouse chromosomes

F(1) backcrosses involving the DDK and C57BL/6 inbred mouse strains show transmission ratio distortion at loci on two different chromosomes, 11 and X. Transmission ratio distortion on chromosome X is restricted to female offspring while that on chromosome 11 is present in offspring of both sexes. In this article we investigate whether the inheritance of alleles at loci on one chromosome is independent of inheritance of alleles on the other. A strong nonrandom association between the inheritance of alleles at loci on both chromosomes is found among male offspring, while independent assortment occurs among female offspring. We also provide evidence that the mechanism by which this phenomenon occurs involves preferential cosegregation of nonparental chromatids of both chromosomes at the second meiotic division, after the ova has been fertilized by a C57BL/6 sperm bearing a Y chromosome. These observations confirm the influence of the sperm in the segregation of chromatids during female meiosis, and indicate that a locus or loci on the Y chromosome are involved in this instance of meiotic drive.     

Evolutionary strata on the chicken Z chromosome: implications for sex chromosome evolution

The human X chromosome exhibits four "evolutionary strata," interpreted to represent distinct steps in the process whereby recombination became arrested between the proto X and proto Y. To test if this is a general feature of sex chromosome evolution, we studied the Z-W sex chromosomes of birds, which have female rather than male heterogamety and evolved from a different autosome pair than the mammalian X and Y. Here we analyze all five known gametologous Z-W gene pairs to investigate the "strata" hypothesis in birds. Comparisons of the rates of synonymous substitution and intronic divergence between Z and W gametologs reveal the presence of at least two evolutionary strata spread over the p and q arms of the chicken Z chromosome. A phylogenetic analysis of intronic sequence data from different avian lineages indicates that Z-W recombination ceased in the oldest stratum (on Zq; CHD1Z, HINTZ, and SPINZ) 102-170 million years ago (MYA), before the split of the Neoaves and Eoaves. However, recombination continued in the second stratum (on Zp; UBAP2Z and ATP5A1Z) until after the divergence of extant avian orders, with Z and W diverging 58-85 MYA. Our data suggest that progressive and stepwise cessation of recombination is a general feature behind sex chromosome evolution.     

Heteromorphic Z and W sex chromosomes in Physalaemus ephippifer (Steindachner, 1864) (Anura, Leiuperidae)

Heteromorphisms between sex chromosomes are rarely found in anurans and sex chromosome differentiation is considered to be a set of recent recurrent events in the evolutionary history of this group. This paper describes for the first time heteromorphic sex chromosomes Z and W in the leiuperid genus Physalaemus. They were found in P. ephippifer, a species of the P. cuvieri group, and corresponded to the eighth pair of its karyotype. The W chromosome differed from the Z chromosome by the presence of an additional segment in the short arm, composed of a distal NOR and an adjacent terminal DAPI-positive C-band. The identification of this sex chromosome pair may help in future investigations into the sex determining genes in the genus Physalaemus.     

白豆杉的核型和性染色体的研究

白豆杉pseudotaxus chienii(Cheng)Cheng是我国裸子植物特有属之一,雌雄异常,根尖 细胞染色体分析表明：雌株有一对异形性染色体,异配性别,属ZW型;雄株是同配性别,属ZZ型,雌株的型为2n=2x=24=22m(2SAT ZW) 2T,雄株的核型为2n=2x=24=22m(2SAT ZZ) 2T。Giemsa C-带,显示,Z染色体长短臂均具端带,W染色体不显带。     

Sex Determination in the Fly Megaselia Scalaris, a Model System for Primary Steps of Sex Chromosome Evolution

The fly Megaselia scalaris Loew possesses three homomorphic chromosome pairs; 2 is the sex chromosome pair in two wild-type laboratory stocks of different geographic origin (designated ``original' sex chromosome pair in this paper). The primary male-determining function moves at a very low rate to other chromosomes, thereby creating new Y chromosomes. Random amplified polymorphic DNA markers obtained by polymerase chain reaction with single decamer primers and a few available phenotypic markers were used in testcrosses to localize the sex-determining loci and to define the new sex chromosomes. Four cases are presented in which the primary male-determining function had been transferred from the original Y chromosome to a new locus either on one of the autosomes or on the original X chromosome, presumably by transposition. In these cases, the sex-determining function had moved to a different locus without an obvious cotransfer of other Y chromosome markers. Thus, with Megaselia we are afforded an experimental system to study the otherwise hypothetical primary stages of sex chromosome evolution. An initial molecular differentiation is apparent even in the new sex chromosomes. Molecular differences between the original X and Y chromosomes illustrate a slightly more advanced stage of sex chromosome evolution.     

Single locus sex determination and female heterogamety in the basket willow (Salix viminalis L.)

Most eukaryotes reproduce sexually and a wealth of different sex determination mechanisms have evolved in this lineage. Dioecy or separate sexes are rare among flowering plants but have repeatedly evolved from hermaphroditic ancestors possibly involving male or female sterility mutations. Willows (Salix spp.) and poplars (Populus spp.) are predominantly dioecious and are members of the Salicaceae family. All studied poplars have sex determination loci on chromosome XIX, however, the position differs among species and both male and female heterogametic system exists. In contrast to the situation in poplars, knowledge of sex determination mechanisms in willows is sparse. In the present study, we have for the first time positioned the sex determination locus on chromosome XV in S. viminalis using quantitative trait locus mapping. All female offspring carried a maternally inherited haplotype, suggesting a system of female heterogamety or ZW. We used a comparative mapping approach and compared the positions of the markers between the S. viminalis linkage map and the physical maps of S. purpurea, S. suchowensis and P. trichocarpa. As we found no evidence for chromosomal rearrangements between chromosome XV and XIX between S. viminalis and P. trichocarpa, it shows that the sex determination loci in the willow and the poplar most likely do not share a common origin and has thus evolved separately. This demonstrates that sex determination mechanisms in the Salicaceae family have a high turnover rate and as such it is excellent for studies of evolutionary processes involved in sex chromosome turnover.     

Triploidy in a sexually dimorphic passerine provides new evidence for the effect of the W chromosome on secondary sexual traits in birds

In birds, there are two main models for the determination of sex: the ‘Z Dosage’ model in which the number, or dose, of Z chromosomes determines sex, and the ‘Dominant W’ model which argues that a specific gene in the W chromosome may influence Z gene expression and determine sex. The best evidence for W determination of sex comes from birds with 2 copies of the Z chromosome paired with a single W (e.g. ZZW) which are nonetheless females. Here, we expand the species where such a mechanism may operate by reporting a case of a triploid Neotropical passerine bird with sexually dimorphic plumage, the São Paulo marsh antwren Formicivora paludicola. Evidence from 17 autosomal unlinked microsatellite loci, and CHD1 sex‐linked locus, indicate that this individual is a 3n ZZW triploid with intermediate plumage pattern. This example expands our knowledge of sex determination mechanisms in birds by demonstrating that both the W and the two Z chromosomes affect the expression of morphological secondary sexual traits in a non‐galliform bird.     

Resolution of sex chromosome constitution by genomic in situ hybridization and fluorescence in situ hybridization with (TTAGG) n telomeric probe in some species of Lepidoptera

We have developed a simple method to resolve the sex chromosome constitution in females of Lepidoptera by using a combination of genomic in situ hybridization (GISH) and fluorescence in situ hybridization with (TTAGG) _n telomeric probe (telomere-FISH). In pachytene configurations of sex chromosomes, GISH differentiated W heterochromatin and telomere-FISH detected the chromosome ends. With this method we showed that Antheraea yamamai has a standard system with a fully differentiated W–Z sex chromosome pair. In Orgyia antiqua, we confirmed the presence of neo-W and neo-Z chromosomes, which most probably originated by fusion of the ancestral W and Z with an autosome pair. In contrast to earlier data, Orgyia thyellina females displayed a neo-ZW₁W₂ sex chromosome constitution. A neo-WZ₁Z₂ trivalent was found in females of Samia cynthia subsp. indet., originating from a population in Nagano, Japan. Whereas another subspecies collected in Sapporo, Japan, and determined as S. cynthia walkeri, showed a neo-W/neo-Z bivalent similar to O. antiqua, and the subspecies S. cynthia ricini showed a Z univalent (a Z/ZZ system). The combination of GISH and telomere-FISH enabled us to acquire not only reliable information about sex chromosome constitution but also an insight into sex chromosome evolution in Lepidoptera.     

Molecular and whole-plant responses to selection for enzyme activity in alfalfa root nodules: evidence for molecular compensation of aspartate aminotransferase expression

Summary The enzyme aspartate aminotransferase (AAT) plays a key role in the assimilation of fixed-N in alfalfa (Medicago sativa L.) root nodules. AAT activity in alfalfa nodules is due to the activity of two dimeric isozymes, AAT-1 and AAT-2, that are products of two distinct genes. Three forms of AAT-2 (AAT-2a, -2b, and-2c) have been identified. It was hypothesized that two alleles occur at the AAT-2 locus, giving rise to the three AAT-2 enzymes. In a prior study bidirectional selection for root nodule AAT and asparagine synthetase (AS) activities on a nodule fresh weight basis in two diverse alfalfa germ plasms resulted in high nodule enzyme activity subpopulations with about 20% more nodule AAT activity than low enzyme activity subpopulations. The objectives of the study presented here were to determine the inheritance of nodule AAT-2 production and to evaluate the effect of bidirectional selection for AAT and AS on AAT-2 allelic frequencies, the relative contributions of AAT-1 and AAT-2 to total nodule activity, nodule enzyme concentration, and correlated traits. Two alleles at the AAT-2 locus were verified by evaluating segregation of isozyme phenotypes among F₁ and S₁ progeny of crosses or selfs. Characterization of subpopulations for responses associated with selection was conducted using immunoprecipitation of in vitro nodule AAT activity, quantification of AAT enzyme protein by ELISA, and AAT activity staining of native isozymes on PAGE. Results indicate that selection for total AAT activity specifically altered the expression of the nodule AAT-2 isozyme. AAT-2 activity was significantly greater in high compared to low activity subpopulations, and high AAT subpopulations from both germ plasms had about 18% more AAT-2 enzyme (on a nodule fresh weight basis). No significant or consistent changes in AAT-2 genotypic frequencies in subpopulations were caused by selection for AAT activity. Since changes in AAT activity were not associated with changes in AAT-2 genotype, selection must have affected a change(s) at another locus (or loci), which indirectly effects the expression of nodule AAT.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products or vendors that might also be suitable     

Genetic evidence for linkage with the Z and W sex chromosomes of two distinct couples of alleles controlling larval and postmetamorphic skin pigmentation in salamander

In Pleurodeles waltl, progeny resulting from a cross between 2 individuals of the Z/W sexual genotype include 25% of W/W individuals, while those issued from crossing a Z/W neomale with a W/W thelygenous female include 50% of W/W individuals. W/W individuals can be identified through the peptidase-1 zymogram since, in P. waltl, this enzyme is controlled by codominant alleles which are linked to the sex chromosomes. In such progeny, we discovered 2 mutant phenotypes affecting larval and postmetamorphic skin pigmentation in W/W individuals. These phenotypes are described herein. The study of their inheritance in several offspring provides evidence that they are controlled by 2 distinct genes, the recessive mutant alleles of which are linked to the W sex chromosome; moreover, in thelygenous W/W females, the differential segment does not prevent the occurrence of meiotic recombinations between W sex chromosomes. Mutant skin pigmentary phenotypes are easily identified and constitute a tool for rapid, efficient selection of individuals of the W/W sexual genotype.     

Recombination is suppressed over a large region of the rainbow trout Y chromosome

The previous genetic mapping data have suggested that most of the rainbow trout sex chromosome pair is pseudoautosomal, with very small X-specific and Y-specific regions. We have prepared an updated genetic and cytogenetic map of the male rainbow trout sex linkage group. Selected sex-linked markers spanning the X chromosome of the female genetic map have been mapped cytogenetically in normal males and genetically in crosses between the OSU female clonal line and four different male clonal lines as well as in outcrosses involving outbred OSU and hybrids between the OSU line and the male clonal lines. The cytogenetic maps of the X and Y chromosomes were very similar to the female genetic map for the X chromosome. Five markers on the male maps are genetically very close to the sex determination locus ( SEX ), but more widely spaced on the female genetic map and on the cytogenetic map, indicating a large region of suppressed recombination on the Y chromosome surrounding the SEX locus. The male map is greatly extended at the telomere. A BAC clone containing the SCAR (sequence characterized amplified region) Omy - 163 marker, which maps close to SEX , was subjected to shotgun sequencing. Two carbonyl reductase genes and a gene homologous to the vertebrate skeletal ryanodine receptor were identified. Carbonyl reductase is a key enzyme involved in production of trout ovarian maturation hormone. This brings the number of type I genes mapped to the sex chromosome to six and has allowed us to identify a region on zebrafish chromosome 10 and medaka chromosome 13 which may be homologous to the distal portion of the long arm of the rainbow trout Y chromosome.     

我国部分地方鸡种肤色伴性遗传初步观察

对泰和鸡、仙居鸡、固始鸡、北京油鸡、萧山鸡、狼山鸡（Ｎ系）进行肤色伴性遗传观察,结果表明：泰和鸡常染色体上含有１对黑色素基因ＰＰ,仙居鸡、萧山鸡、北京油鸡性染色体上含有Ｉｄ抑制色素基因,狼山鸡、固始鸡、泰和鸡性染色体上含有ｉｄ基因,泰和鸡♂与含有Ｉｄ基因鸡种（仙居鸡、萧山鸡、北京油鸡）♀杂交,Ｆ１代肤色能自别雌雄,公鸡为黄皮肤,母鸡为黑皮肤。