A cytological study of two closely related blackfly species: Cnephia dacotensis and Cnephia ornithophilia (Diptera: Simuliidae)

1975 ◽  
Vol 53 (11) ◽  
pp. 1622-1637 ◽  
Author(s):  
William S. Procunier
Keyword(s):  
Light Microscopy ◽  
Polytene Chromosome ◽  
Sex Chromosomes ◽  
Cytological Study ◽  
Molecular Model ◽  
Crossing Over ◽  
X Chromosomes ◽  
Synaptonemal Complexes ◽  
Y Chromosomes

Cnephia dacotensis and C. ornithophilia are two closely related blackfly species. Their polytene chromosome complements differ in three interspecific inversions, in separate inversion polymorphisms, and the presence of specific sex chromosomes of C. dacotensis. These sex chromosomes comprise four structurally different X chromosomes and two structurally different Y chromosomes. A molecular model is proposed for their evolution. Light microscopy revealed that both species have male achiasmate meiosis. Male larvae of C. dacotensis lack synaptonemal complexes. Random association of inversions IIIS-1 and IIIL-1 and the presence of synaptonemal complexes indicate that crossing-over occurs in the female.

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

DIFFERENTIAL DNA REPLICATION IN THE XX AND XY CELLS OF MUSCA DOMESTICA L. OCRA STRAIN

1970 ◽  
Vol 12 (3) ◽  
pp. 461-473 ◽  
Author(s):  
K. Y. Jan ◽  
J. W. Boyes
Keyword(s):  
Dna Replication ◽  
Musca Domestica ◽  
Sex Chromosomes ◽  
Chromosome Length ◽  
Final Part ◽  
X Chromosomes ◽  
Y Chromosomes ◽  
Heteromorphic Sex Chromosomes ◽  
Autosomal Pair ◽  
Differential Dna Replication

The karyotype of Musca domestica L. ocra strain, consists of the sex chromosomes and five autosomal pairs. The heteromorphic sex chromosomes are heterochromatic and mitotically unpaired, whereas the autosomes are euchromatic and mitotically paired. All autosomal pairs and both X and Y chromosomes are cytologically recognizable.The relative labelling rate, R (in terms of the number of grains counted per 100 labelled metaphases per μ of chromosome length) for the sex chromosomes and for each autosomal pair was followed from 1.5 hours to 8 hours after H3TdR injection. The pattern of labelling rate was similar for the different autosomal pairs in the XX cells but this pattern for the autosomal pairs in the XY cells, though also similar for the different pairs, differed appreciably from that found in the XX cells. The pattern of the labelling rate for the X chromosomes was similar in the XX and XY cells. Also the pattern of labelling rate for the X and Y chromosomes was similar during the final part of the replication period. The two X chromosomes in the XX cells and the X and Y chromosomes in the XY cells completed labelling later than the autosomes.

Sex Chromosome Translocations

2018 ◽  
Author(s):  
R. J McKinlay Gardner ◽  
David J Amor
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Transcriptional Silencing ◽  
The Other ◽  
X Chromosomes ◽  
Chromosome Form ◽  
Chromosome Translocations ◽  
Y Chromosomes ◽  
Autosomal Translocation

The sex chromosomes (gonosomes) are different, and sex chromosome translocations need to be considered separately from translocations between autosomes. A sex chromosome can engage in translocation with an autosome, with the other sex chromosome, or even with its homolog. The qualities of the sex chromosomes have unique implications in terms of the genetic functioning of gonosome-autosome translocations. This chapter acknowledges the specific peculiarities that the sex chromosomes imply: the X being subject to transcriptional silencing; and the very small Y gene complement being confined largely to sex-determining loci. It reviews translocations between sex chromosomes and autosomes; between X and Y chromosomes; and even the very rare circumstance of between X chromosomes and between Y chromosomes. The differences in assessing risk, according to chromosome form, in comparison with the autosomal translocation, are reviewed, and the biology behind these differences is discussed.

A cytogenetic survey of 25 species of lower termites from Australia

Genome ◽  
1990 ◽  
Vol 33 (1) ◽  
pp. 80-88 ◽  
Author(s):  
Peter Luykx
Keyword(s):  
Sex Determination ◽  
Sex Chromosomes ◽  
Common Ancestor ◽  
Systematic Position ◽  
Necessary Condition ◽  
X Chromosomes ◽  
Y Chromosomes ◽  
Cytogenetic Survey ◽  
The Difference ◽  
High Degree

A survey of 25 species of lower termites (families Mastotermitidae, Termopsidae, and Kalotermitidae) in Australia revealed that centric fusions are a common theme in karyotype evolution in these insects. All but one of the species studied have a basic XX/XY mechanism of sex determination, secondarily complicated in about a third of a species by centric fusions between autosomes and sex chromosomes. There is no obvious relationship between systematic position and presence or absence of these fusions. Fusions between Y chromosomes and autosomes were more common than fusions between X chromosomes and autosomes, in accord with the prediction of the hypothesis that differential selection between the two sexes is the basis for the spread of sex-linked fusions. The absence of these fusions in many species does not favor the idea that a high degree of sex linkage is a necessary condition for the establishment or maintenance of eusocial behavior in termites. The difference in the mechanism of sex determination from that of cockroaches (XX/XO) argues against the evolutionary derivation of termites from ancestral cockroaches; derivation of both groups from some common ancestor with XX/XY sex determination is more likely.Key words: termites, karotype, evolution, sex chromosomes, Australia.

C-banded karyotypes of two Silene species with heteromorphic sex chromosomes

Genome ◽  
2002 ◽  
Vol 45 (2) ◽  
pp. 243-252 ◽  
Author(s):  
Aleksandra Grabowska-Joachimiak ◽  
Andrzej Joachimiak
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Silene Latifolia ◽  
Silene Dioica ◽  
Dna Amount ◽  
Metaphase Chromosomes ◽  
X Chromosomes ◽  
C Banding ◽  
Y Chromosomes ◽  
Heteromorphic Sex Chromosomes

Mitotic metaphase chromosomes of Silene latifolia (white campion) and Silene dioica (red campion) were studied and no substantial differences between the conventional karyotypes of these two species were detected. The classification of chromosomes into three distinct groups proposed for S. latifolia by Ciupercescu and colleagues was considered and discussed. Additionally, a new small satellite on the shorter arm of homobrachial chromosome 5 was found. Giemsa C-banded chromosomes of the two analysed species show many fixed and polymorphic heterochromatic bands, mainly distally and centromerically located. Our C-banding studies provided an opportunity to better characterize the sex chromosomes and some autosome types, and to detect differences between the two Silene karyotypes. It was shown that S. latifolia possesses a larger amount of polymorphic heterochromatin, especially of the centromeric type. The two Silene sex chromosomes are easily distinguishable not only by length or DNA amount differences but also by their Giemsa C-banding patterns. All Y chromosomes invariably show only one distally located band, and no other fixed or polymorphic bands on this chromosome were observed in either species. The X chromosomes possess two terminally located fixed bands, and some S. latifolia X chromosomes also have an extra-centric segment of variable length. The heterochromatin amount and distribution revealed by our Giemsa C-banding studies provide a clue to the problem of sex chromosome and karyotype evolution in these two closely related dioecious Silene species.Key words: dioecious plant, Silene dioica, Silene latifolia, karyotype, sex chromosomes, heterochromatin, C-banding.

scholarly journals MITOTIC RECOMBINATION IN THE HETEROCHROMATIN OF THE SEX CHROMOSOMES OF DROSOPHILA MELANOGASTER

Genetics ◽  
1978 ◽  
Vol 90 (1) ◽  
pp. 93-104
Author(s):  
P Ripoll ◽  
A Garcia-Bellido
Keyword(s):  
Drosophila Melanogaster ◽  
Y Chromosome ◽  
Sex Chromosomes ◽  
Mitotic Recombination ◽  
X Chromosomes ◽  
X Ray ◽  
Y Chromosomes ◽  
Chromosome Arm

ABSTRACT The frequency of spontaneous and X-ray-induced mitotic recombination involving the Y chromosome has been studied in individuals with a marked Y chromosome arm and different XY compound chromosomes. The genotypes used include X chromosomes with different amounts of X heterochromatin and either or both arms of the Y chromosome attached to either side of the centromere. Individuals with two Y chromosomes have also been studied. The results show that the bulk of mitotic recombination takes place between homologous regions.

Extensive pairing of the XY bivalent in mouse spermatocytes as visualized by whole-mount electron microscopy

1977 ◽  
Vol 25 (1) ◽  
pp. 1-15
Author(s):  
L.L. Tres
Keyword(s):  
Sex Chromosomes ◽  
Detergent Solution ◽  
Lateral Element ◽  
Synaptonemal Complexes ◽  
Pairing Segment ◽  
Y Chromosomes ◽  
Cell Dispersion ◽  
Whole Mount ◽  
Xy Bivalent ◽  
Microscope Technique

Autosomes and sex chromosomes of mouse spermatocytes were examined during zygotene, pachytene, and diplotene by a whole-mount electron-microscope technique after cell dispersion in a detergent solution (Nonidet-P40). Zygotene, pachytene, and diplotene stages can be adequately identified in the preparations. Thus, asynchronous side-by-side pairing of homologous autosomes, some of them displaying attached nucleoli, defines zygotene. Pachytene is identified by complete pairing of homologues. Diplotene is characterized by disjunction of bivalents (autosomes and sex chromosomes), lack of autosomal-attached nucleoli, divergent expansions observed at lateral element endings of disassembled synaptonemal complexes, end-to-end association of the XY pair and well defined outward deformations (‘bulges’) along sex chromosomal axial cores. X and Y chromosomes display at pachytene an extensive side-by-side pairing segment which decreases in length as meiotic prophase advances. Each sex chromosomal axial core appears double and is formed by close apposition of 2 nearly parallel elements displayed separately along the entire length of the chromosomal core. This double structural feature suggests that each sex chromosomal axial core is presumably composed of 2 chromatid axial cores, each of which, in turn, constitutes the respective lateral elements of short synaptonemal complexes observed at the unpaired segment.

The Synaptonemal Complex and the Achiasmatic Condition

1973 ◽  
Vol 13 (1) ◽  
pp. 83-95 ◽  
Author(s):  
S. STACK
Keyword(s):  
Light Microscopy ◽  
Microscopic Examination ◽  
Three Dimensional ◽  
Electron Microscopic Examination ◽  
Chiasma Formation ◽  
Crossing Over ◽  
Electron Microscopic ◽  
Synaptonemal Complexes ◽  
Chromosome Arrangements ◽  
Onion Species

The onion species Allium amplectans includes both a triploid and a tetraploid variety. By light microscopy both varieties appear to have normal synapsis during pachytene of meiosis. However, the triploid does not form chiasmata and exhibits almost total asynapsis following pachytene. The tetraploid forms at least one chiasma per homologue and retains pairing through metaphase I. Electron-microscopic examination of pachytene nuclei in these 2 varieties reveals apparently identical synaptonemal complexes. Three-dimensional reconstructions of chromosome arrangements in triploid pachytene nuclei confirm that synapsis is as complete as could be expected in an autotriploid. These observations give firm support to the hypothesis that the presence of apparently structurally normal synaptonemal complexes is not a sufficient prerequisite to ensure chiasma formation. It is suggested that a faulty or missing endonuclease which is normally involved in crossing over is responsible for the achiasmatic condition in triploid A. amplectans.

A cytological study of species in Cnephia s. str. (Diptera: Simuliidae)

1982 ◽  
Vol 60 (11) ◽  
pp. 2866-2878 ◽  
Author(s):  
William S. Procunier
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Cytological Study ◽  
Chromosome Complement ◽  
Nucleolar Organizer ◽  
Sympatric Speciation ◽  
Basic Chromosome ◽  
Y Chromosomes ◽  
Norwegian Population ◽  
Sex Chromosome System

Cytological descriptions and phylogenetic relationships are presented for the genus Cnephia s. str. All members are male achiasmate. Cnephia lapponica is unique in that its basic chromosome complement is reduced from n = 3 to n = 2 metacentrics as a result of a fusion of chromosomes II and III. Sex chromosome differentiation varies from nonobservable in C. ornithophilia and C. eremites through C. pecuarum in which the standard and IS-5 sequences are distributed differentially over X and Y chromosomes, to the polytypic system of C. lapponica in which the X chromosome is fixed for expression of the nucleolar organizer (NO) and the Y chromosome for nonexpression. Further, in a Norwegian population of C. lapponica, males are additionally interchange heterozygotes. Thus, a multiple sex chromosome system exists in which all the chromosomes are sex chromosomes. Closest members occur sympatrically and differ by sex chromosomes and at least one fixed inversion; more distant taxa differ by a number of fixed inversions as well as sex chromosomes. The identical bands 17B and 24C, which appear in a thin or enhanced form, are polymorphic, sex-linked, fixed, or lost in different members of the group. This study supports a model for sympatric speciation.

Mixed-Up Sex Chromosomes: Identification of Sex Chromosomes in the X1X1X2X2/X1X2Y System of the Legless Lizards of the Genus Lialis (Squamata: Gekkota: Pygopodidae)

2016 ◽  
Vol 149 (4) ◽  
pp. 282-289 ◽  
Author(s):  
Michail Rovatsos ◽  
Martina Johnson Pokorná ◽  
Marie Altmanová ◽  
Lukáš Kratochvíl
Keyword(s):  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Comparative Genomic ◽  
X Chromosomes ◽  
Telomeric Sequences ◽  
Multiple Sex Chromosomes ◽  
Y Chromosomes ◽  
Heteromorphic Sex Chromosomes ◽  
Cytogenetic Analyses ◽  
Male Heterogamety

Geckos in general show extensive variability in sex determining systems, but only male heterogamety has been demonstrated in the members of their legless family Pygopodidae. In the pioneering study published more than 45 years ago, multiple sex chromosomes of the type X1X1X2X2/X1X2Y were described in Burton's legless lizard (Lialisburtonis) based on conventional cytogenetic techniques. We conducted cytogenetic analyses including comparative genomic hybridization and fluorescence in situ hybridization (FISH) with selected cytogenetic markers in this species and the previously cytogenetically unstudied Papua snake lizard (Lialis jicari) to better understand the nature of these sex chromosomes and their differentiation. Both species possess male heterogamety with an X1X1X2X2/X1X2Y sex chromosome system; however, the Y and one of the X chromosomes are not small chromosomes as previously reported in L. burtonis, but the largest macrochromosomal pair in the karyotype. The Y chromosomes in both species have large heterochromatic blocks with extensive accumulations of GATA and AC microsatellite motifs. FISH with telomeric probe revealed an exclusively terminal position of telomeric sequences in L. jicari (2n = 42 chromosomes in females), but extensive interstitial signals, potentially remnants of chromosomal fusions, in L.burtonis (2n = 34 in females). Our study shows that even largely differentiated and heteromorphic sex chromosomes might be misidentified by conventional cytogenetic analyses and that the application of more sensitive cytogenetic techniques for the identification of sex chromosomes is beneficial even in the classical examples of multiple sex chromosomes.

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