Spontaneous Crossing-over between X- and Y-Chromosomes in Drosophila melanogaster

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.

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EXTRACHROMOSOMAL ELEMENT DELTA IN DROSOPHILA MELANOGASTER. IX. INDUCTION OF DELTA-RETAINING CHROMOSOME LINES BY MUTATION AND GENE MAPPING

Genetics ◽

10.1093/genetics/74.3.477 ◽

1973 ◽

Vol 74 (3) ◽

pp. 477-487

Author(s):

Sumio Minamori ◽

Kinue Sugimoto

Keyword(s):

Drosophila Melanogaster ◽

Crossing Over ◽

Chromosomal Gene ◽

Ethyl Methane Sulfonate ◽

Methane Sulfonate ◽

Multiple Alleles ◽

Ethyl Methane ◽

Extrachromosomal Element ◽

Polygenic System ◽

Killing Action

ABSTRACT [Delta b], symbolized as [δb], is retained by Sb chromosome lines and transmitted through the females to their progeny. Transmission through the males is not directly demonstrable (Minamori 1969a). [delta r], symbolized as [δr], is retained by Sr chromosome lines and transmitted biparentally (Minamori 1971). The multiplication of delta is suppressed at low temperature. All descendant lines derived from Sb-carrying or Sr-carrying flies in which the presence of delta cannot be demonstrated gradually accumulate their specific delta factors over many generations (Minamori 1969b, 1972). The delta factors and the sensitive chromosomes are inseparably associated. This observation led to the assumption that delta may be a copy of a chromosomal gene or a certain agent integrated into the chromosome (Minamori 1972). This assumption was examined in the present study by experiments designed to induce delta-retaining sensitive chromosomes, and to map the gene(s) responsible for delta-retention and/or for sensitivity to the killing action of delta factor. One sensitive chromosome which retained [δb] (Sb chromosome) was obtained in the presence of [δb] out of 2492 insensitive chromosomes which retained no delta; in addition one Sb chromosome was obtained in the presence of [δr] out of 2131 insensitives. The latter finding suggests that Sb might be induced by a mutation caused by [δb] or [δr], but not by integration of either delta into the chromosome. Four Sb chromosomes and one sensitive chromosome which retained [δr] (Sr chromosome) were obtained out of 1970 insensitives when males carrying the chromosome were fed an alkylating mutagen, ethyl methane sulfonate (EMS). The location of delta-retaining genes was examined by crossing-over experiments employing eight Sb and five Sr chromosomes. The genes on these chromosomes were found to be located in the same region or near one another. The gene for [δb], symbolized as Dab, and the gene for [δr], symbolized as Dar, are assumed to be multiple alleles of a locus at 2-24.9. The sensitivity of the chromosomes was modified appreciably by recombination; hence, the genes controlling this trait are assumed to be a polygenic system. The findings obtained in this study lead to the hypothesis that delta may be produced by a chromosomal gene (Da) and transmitted extrachromosomally.

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ORIENTATION DISRUPTOR (ord): A RECOMBINATION-DEFECTIVE AND DISJUNCTION-DEFECTIVE MEIOTIC MUTANT IN DROSOPHILA MELANOGASTER

Genetics ◽

10.1093/genetics/84.3.545 ◽

1976 ◽

Vol 84 (3) ◽

pp. 545-572

Author(s):

James M Mason

Keyword(s):

Drosophila Melanogaster ◽

Genetic Map ◽

Crossing Over ◽

Prophase I ◽

Sister Chromatids

ABSTRACT The effects of a semidominant autosomal meiotic mutant, orientation disruptor (symbol: ord), located at 2-103.5 on the genetic map and in region 59B-D of the salivary map, have been examined genetically and cytologically. The results are as follows. (1) Crossing over in homozygous females is reduced to about seven percent of controls on all chromosomes, with the reduction greatest in distal regions. (2) Crossing over on different chromosomes is independent. (3) Reductional nondisjunction of any given chromosome is increased to about thirty percent of gametes from homozygous females. The probability of such nondisjunction is the same among exchange and nonexchange tetrads with the exception that a very proximal exchange tends to regularize segregation. (4) Equational nondisjunction of each chromosome is increased to about ten percent of gametes in homozygous females; this nondisjunction is independent of exchange. (5) The distributive pairing system is operative in homozygous females. (6) In homozygous males, reductional nondisjunction of each chromosome is increased to about ten percent, and equational nondisjunction to about twenty percent, of all gametes. (7) Cytologically, two distinct meiotic divisions occur in spermatocytes of homozygous males. The first division looks normal although occasional univalents are present at prophase I and a few lagging chromosomes are seen at anaphase I. However, sister chromatids of most chromosomes have precociously separated by metaphase II. Possible functions of the ord+ gene are considered.

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Reciprocal recombination and the evolution of the ribosomal gene family of Drosophila melanogaster.

Genetics ◽

10.1093/genetics/122.3.617 ◽

1989 ◽

Vol 122 (3) ◽

pp. 617-624 ◽

Cited By ~ 1

Author(s):

S M Williams ◽

J A Kennison ◽

L G Robbins ◽

C Strobeck

Keyword(s):

Drosophila Melanogaster ◽

Gene Family ◽

Ribosomal Rna ◽

Natural Populations ◽

Ribosomal Gene ◽

Gene Region ◽

Ribosomal Rna Gene ◽

Reciprocal Recombination ◽

Y Chromosomes ◽

Length Polymorphisms

Abstract The role of reciprocal recombination in the coevolution of the ribosomal RNA gene family on the X and Y chromosomes of Drosophila melanogaster was assessed by determining the frequency and nature of such exchange. In order to detect exchange events within the ribosomal RNA gene family, both flanking markers and restriction fragment length polymorphisms within the tandemly repeated gene family were used. The vast majority of crossovers between flanking markers were within the ribosomal RNA gene region, indicating that this region is a hotspot for heterochromatic recombination. The frequency of crossovers within the ribosomal RNA gene region was approximately 10(-4) in both X/X and X/Y individuals. In conjunction with published X chromosome-specific and Y chromosome-specific sequences and restriction patterns, the data indicate that reciprocal recombination alone cannot be responsible for the observed variation in natural populations.

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