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At least 19 recordsLinked to original sources
PubMed1977

On the components of segregation distortion in Drosophila melanogaster.

The segregation distorter (SD) complex is a naturally occurring meiotic drive system with the property that males heterozygous for an SD-bearing chromosome 2 and an SD(+)-bearing homolog transmit the SD-bearing chromosome almost exclusively. This distorted segregation is the consequence of an induced dysfunction of those sperm that receive the SD(+) homolog. From previous studies, two loci have been implicated in this phenomenon: the Sd locus which is required to produce distortion, and the Responder (Rsp) locus that is the site at which Sd acts. There are two allelic alternatives of Rsp-sensitive (Rsp(sens)) and insensitive (Rsp(ins)); a chromosome carrying Rsp(ins) is not distorted by SD. In the present study, the function and location of each of these elements was examined by a genetic and cytological characterization of X-ray-induced mutations at each locus. The results indicate the following: (1) the Rsp locus is located in the proximal heterochromatin of 2R; (2) a deletion for the Rsp locus renders a chromosome insensitive to distortion; (3) the Sd locus is located to the left of pr (2-54.5), in the region from 37D2-D7 to 38A6-B2 of the salivary chromosome map; (4) an SD chromosome deleted for Sd loses its ability to distort; (5) there is another important component of the SD system, E(SD), in or near the proximal heterochromatin of 2L, that behaves as a strong enhancer of distortion. The results of these studies allow a reinterpretation of results from earlier analyses of the SD system and serve to limit the possible mechanisms to account for segregation distortion.

Alleles↗
PubMed1975

Genetic dissection of segregation distortion II. Mechanism of suppression of distortion by certain inversions.

In(2L+2R)Cgamma and In(2LR)Pm2 are inversion-bearing chromosomes, the former carrying a paracentric inversion in each arm and the latter carrying a long pericentric. Both chromosomes produce normal segregation ratios when present in heterozygous males with certain segregation distorter chromosomes. The apparent suppression of distortion by these chromosomes was long attributed to a failure of synapsis, but this hypothesis has fallen out of favor recently because a large number of chromosome aberrations, particularly translocations and inversions, suppress distortion even though their breakpoints fall into no recognizable pattern. Although failure of synapsis does not appear to be the mechanism of suppression of distortion, what is responsible for the suppression remains unknown. In this paper it is shown that In(2L+2R)Cgamma and In(2LR)Pm2 suppress segregation distortion because they carry Rsp, a component of the segregation distorter system that renders a chromosome insensitive to distortion. Both chromosomes induce "suicide" of chromosomes carrying Sd Rsp+.

Animals↗
PubMed1992

ABO segregation distortion in Visakhapatnam, India.

Distortions in mother-infant, mother-child and father-child segregation for the ABO system as well as in the sex of offspring are described in a sample from a maternity service and from families of Visakhapatnam, India. Some distortions follow the expected fetomaternal incompatibility depression, others the expected feto-maternal induction of tolerance, and some remain unexplained. A differential action of selective factors on male and female fetuses, infants and children was also found, but no hypothesis could be postulated to explain it. The mother-infant matrix was found to be different from the mother-child matrix probably due to the inclusion of the reproductive time only in the mother-infant matrix. Unexpectedly, father-child segregation distortions were also found.

ABO Blood-Group System↗
PubMed1992

Male and female segregation distortion for heterochromatic supernumerary segments on the S8 chromosome of the grasshopper Chorthippus jacobsi.

The mode of inheritance of supernumerary segments located on three different chromosome pairs was investigated in controlled crosses with specimens of the grasshopper Chorthippus jacobsi. While extra segments located on chromosomes M5 and M6 showed Mendelian inheritance, that on S8 did not. Thus, the two supernumerary heterochromatic chromosome segments located distally on the S8 chromosome accumulated through non-Mendelian transmission through both sexes. The observed transmission patterns may be explained by gametic selection for spermatozoa carrying segmented S8 chromosomes, in addition to meiotic drive for segmented S8 chromosomes in heterozygous females. The significance of these findings for the maintenance of these polymorphisms in natural populations is discussed.

Animals↗
PubMed1976

Cytogenetic analysis of homozygous segregation distorter males of Drosophila melanogaster.

Certain homozygous SD males are nearly sterile. Sterility is not due to aneuploid gametes--no significant second chromosome nondisjunction was found in matings to attached-2 and mei-S332 females. Some fourth chromosome aneuploidy was observed here, and in the cytological work. Otherwise, cytology of the meiotic divisions was essentially normal. Early spermatid bundles are normal, sperm head counts approximating the normal 64. In the later, coiled bundle stage, one observes less than 30 heads many of which are grossly abnormal: twisted, club-like, or globular. In double mating experiments, SD/SD sperm did not displace normal sperm introduced first. In the reverse experiment, sperm (or fluid) from SD/SD males markedly reduced capacity of the females to store and utilize sperm from normal males, as scored from progeny and by counts of stored sperm. No sperm were seen in the storage organs of females imseminated first by SD/SD then by normal males. Many females refuse such a second mating. Our observations are quantitatively different from those with heterozygous SD males, but qualitatively similar, supporting the view that the near sterility of homozygous SD males arises from a mechanism of sperm dysfunction like that in SD/+ males.

Animals↗
PubMed1979

Segregation distortion of the alpha 1-antitrypsin Pi Z allele.

alpha 1-antitrypsin (alpha 1AT) of the Pi type Z is associated with two diseases: pulmonary emphysema and cirrhosis of the liver. We report 23 families with both parents heterozygous for the PiZ allele, characterized from our own analysis and from world literature sources. All families were identified through members expressing disease. From the extended pedigrees, 18 backcross families (parents with Pi types MM and MZ) were identified. Analysis of the backcross families reveals a significant increase in Pi MZ offspring (.73) among families where the male is heterozygous. The distortion is not detected among families where the female is heterozygous. Among the matings where both parents are heterozygous, we found 0.43 Pi ZZ from families where one or more members expressed hepatic cirrhosis, and 0.40 Pi ZZ for total families studied. This contrasts to the 0.25 Pi ZZ expected, but is consistent with the distortion observed in backcross matings. The implications of various statistical approaches are discussed, and we point out why our findings differ from previous reports. We suggest a possible biological explanation residing in the fertilization process.

Alleles↗
PubMed1977

Mechanism of a case of genetic coadaptation in populations of Drosophila melanogaster.

A cryptic polymorphism found in natrual populations of Drosophila melanogaster has been examined in an artificial population maintained for over 200 generations. The polymorphism is selected because it is insensitive to the segregation distorter phenomenon, and it thereby largely preserves the Mendelian rules of segregation. Segregation distorter chromosomes and the cryptic polymorphism form part of a coadapted complex which is associated with linkage disequilibrium in natrual populations.

Animals↗
PubMed1977

Problem of sex ratio in cases of type I syndactyly.

Fifty pedigrees of type I syndactyly were analysed for sex ratio and segreation pattern. Thirty-four of the pedigrees were from the published reports; 16 were collected in the State of Utah. Pedigrees with affected individuals showing webbing between the second and third toes are characterized by a sex ratio of affected individuals favouring males and a highly significant excess of affected sons of heterozygous fathers. A similar distorted segregation pattern is present in those pedigrees when the webbing involves the second and third toes and/or the third and fourth fingers, but not in those pedigrees when the webbing involves other digits. The reason for the distorted segregation pattern is unknown. Hypothesis include abnormal chromosome segregation and gametic selection.

Female↗
PubMed2026

Diploids derived from polyploids: genetic characteristics of four novel interspecific Sorghum populations.

Polyploidy has repeatedly shaped grass evolution, yet direct observations of how polyploid-derived chromosomes behave when returned to diploidy remain rare. Interspecific crosses between diploid Sorghum bicolor and tetraploid hybrids derived from Sorghum halepense generate mixed-ploidy progeny, providing an opportunity to examine chromosome transmission during the early stages of diploidization. Using genome-wide SNP markers, we characterized chromosomal inheritance patterns in 2 diploid and 2 tetraploid families derived from these crosses. Genotype-dosage profiles alone distinguished diploids from tetraploids with complete accuracy, reflecting strong ploidy-dependent differences in dosage-class distributions. Although diploid progeny retained much of the halepense-derived genomic background, several genomic intervals exhibited extended, nonrandom runs of S. bicolor homozygosity that remained polymorphic in corresponding tetraploid populations. These patterns, together with recurrent segregation distortion across independent families, suggest that the transition from tetraploidy to diploidy can expose allelic combinations that differ in transmission or viability. Analyses of flowering time further indicated that diploid and tetraploid derivatives possess distinct genomic architectures, with major association peaks occurring in different chromosomal regions across ploidy levels. Collectively, these results indicate that early diploidization involves nonrandom retention and loss of parental haplotypes shaped by both selective and structural constraints. The diploid extractions characterized here provide a rare empirical system for investigating the early stages of diploidization and a practical framework for studying and eventually mobilizing polyploid-derived variation for sorghum germplasm development. However, broader integration into elite breeding programs will require additional evaluation of cross-fertility, meiotic behavior, and chromosomal stability across diverse breeding backgrounds.

Sorghum↗
PubMed2026

Inducing fixation of transgenic alleles in open-pollinated populations.

The progeny of chlorsulfuron-resistant forage rape (Brassica napus L. subsp. napus, cv. Giant) and potato (Solanum tuberosum L. cv. Iwa) plants hemizygous for a single transgenic locus were screened for transgene segregation following an application of either water or chlorsulfuron. The transgenic locus contained three transgenes conferring kanamycin resistance (NOS-NPTII-NOS), β-glucuronidase (GUS) activity (35S-GUS-OCS), and chlorsulfuron resistance (a complete acetohydroxyacid synthase gene with a proline197 to serine substitution). In the absence of the herbicide application, plants segregated for GUS activity as expected for single locus inheritance. However, the progeny of plants sprayed with chlorsulfuron exhibited a highly distorted segregation for GUS activity, with a significant excess of transgenic progeny. Inducing such biased segregation provides a simple treatment to rapidly drive the fixation of transgenic alleles to homozygosity in open pollinated populations during seed increases of new cultivars.

Alleles↗
PubMed2026

Sex without crossovers mimics clonal reproduction in Rhynchospora tenuis.

Meiotic recombination ensures accurate chromosome segregation and promotes genetic diversity by generating crossovers between homologous chromosomes1. Although essential in most sexually reproducing organisms, recombination is variably regulated and can be absent in some lineages, a condition known as achiasmy2. However, obligate achiasmy in both sexes of a sexual species has not been documented. Here we investigate Rhynchospora tenuis, a flowering plant with the lowest known chromosome number and inverted meiosis3. Combining genomics with molecular experiments, we show that R. tenuis undergoes obligate, genome-wide achiasmy in both male and female meiosis. Despite normal early meiotic axis formation, synapsis fails, crossovers are undetectable cytologically and genetically, and univalents persist at metaphase I. Haplotype-specific accumulation of transposable elements generates segregation distortion favouring the transmission of larger, repeat-rich chromosomes. Sexual reproduction is nevertheless retained: fertilization yields viable seeds only when translocation-compatible gametes meet, indicating strong post-meiotic selection against incompatible homozygous combinations. As a result, all surviving offspring are genetically identical, effectively maintaining heterozygosity by sexual reproduction with parental genotype restitution mimicking clonal reproduction. We propose that recombination loss, a low chromosome number, inverted meiosis and selection for compatible gamete combinations together enable faithful segregation and clonal-like inheritance despite sexual reproduction. These findings blur the boundary between sex and clonality, linking genome architecture, recombination loss and transmission bias.

Journal Article↗