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At least 991 records · Page 55Linked to original sources
PubMed1986

The interdependence of mating structure and inbreeding depression.

The level of inbreeding depression depends on the genetic structure and composition of a population, and is not a meaningful concept in its own right. Models are presented for the dynamics of alleles governing mating strategy when viability is determined by generalized heterosis or lethal recessive alleles. It is shown that a protected polymorphism for mating strategy may ensue from generalized heterosis, while lethal recessive alleles may favor the common mating strategy. Further, neither model provides the conditions allowing spread of an allele when rare (protection) which are obtained by assuming as constant the level of inbreeding depression associated with the equilibrium genetic structure dictated by the common mating strategy.

Animals↗
PubMed1982

Directionality of yeast mating-type interconversion.

The mating-type a and alpha alleles of the yeast Saccharomyces cerevisiae interconvert by a transposition-substitution reaction where replicas of the silent mating loci, at HML and HMR, are transmitted to the expressed mating-type locus (MAT). HML is on the left arm and HMR on the right arm, while MAT is in the middle of chromosome III. Cells with the genotype HML alpha HMRa switch mating type efficiently at a frequency of about 86%. Since well over 50% of the cells switch, it is thought that switches do not occur randomly, but are directed to occur to the opposite mating-type allele. In contrast, we report that strains possessing the reverse HMLa HMR alpha arrangement switch (phenotype) inefficiently at a maximum of about 6%. The basis for this apparent reduced frequency of switching is that these strains preferentially yield futile homologous MAT locus switches--that is, MATa to MATa and MAT alpha to MAT alpha--and consequently, most of these events are undetected. We used genetically marked HM loci to demonstrate that alpha cells preferentially choose HMR as donor and a cells preferentially choose HML as donor, irrespective of the genetic content of the silent loci. Because of this feature, HML alpha HMRa strains generate predominantly heterologous while HMLa HMR alpha strains produce predominantly homologous MAT switches. The control for directionality of switching therefore is not at the level of transposing heterologous mating-type information, but only at the level of choosing HML versus HMR as the donor. In strains where the preferred donor locus is deleted, the inefficient donor becomes capable of donating efficiently. Thus the preference seems to be mediated by competition between the HM loci for donating information to MAT.

Alleles↗
PubMed1994

The mating-type locus of Chlamydomonas reinhardtii contains highly rearranged DNA sequences.

The mating-type locus of Chlamydomonas reinhardtii exists as two apparent alleles (mt+ and mt-) that control mating in haploid gametes and sporulation and meiosis in diploid mt+/mt- zygotes. Twelve genes, seven unrelated to life cycle transitions, are tightly linked to mt, suggesting that the locus exerts recombinational suppression. A 1.1 Mb chromosome walk from a gene linked to mt demonstrates that the mt+ and mt- loci carry four intrachromosomal translocations, two inversions, and large deletions and duplications within a 190 kb sector, presumably accounting for the recombinational suppression that extends through 640 kb of flanking homologous DNA. The rearranged domain also carries blocks of mt(+)- and mt(-)-specific sequences, at least one of which includes a mt(+)-specific gene. The locus has the properties of an incipient sex chromosome.

Animals↗
PubMed1990

Genetic exchange in African trypanosomes.

African trypanosomes are important pathogens of humans and domestic animals, but little was known, until recently, of the genetic system of these parasites. Recent results demonstrate the existence of nonobligatory genetic exchange between different stocks of T. brucei. A number of models have been put forward for the mechanism of genetic exchange, including a fusion model with subsequent random loss of chromosomes and a more conventional mendelian system.

Animals↗
PubMed1992

Mating-type gene switching in Saccharomyces cerevisiae.

The study of yeast mating-type (MAT) gene switching has provided insights into several aspects of the regulation of gene expression. MAT switching is accomplished by a highly programmed site-specific homologous recombination event in which mating-type-specific sequences at MAT are replaced by alternative DNA sequences copied from one of two unexpressed donors. The mating-type system has also provided an opportunity to study both the genetic regulation of gene silencing by alterations in chromatin structure, and the basis of preferential recombination between a recipient of genetic information and one of several possible donors.

Alleles↗
PubMed2004

Plants as models for the study of human pathogenesis.

There are many common disease mechanisms used by bacterial pathogens of plants and humans. They use common means of attachment, secretion and genetic regulation. They share many virulence factors, such as extracellular polysaccharides and some type III secreted effectors. Plant and human innate immune systems also share many similarities. Many of these shared bacterial virulence mechanisms are homologous, but even more appear to have independently converged on a common function. This combination of homologous and analogous systems reveals conserved and critical steps in the disease process. Given these similarities, and the many experimental advantages of plant biology, including ease of replication, stringent genetic and reproductive control, and high throughput with low cost, it is proposed that plants would make excellent models for the study of human pathogenesis.

Animals↗
PubMed2003

The monotreme genome: a patchwork of reptile, mammal and unique features?

The first specimen of platypus (Ornithorhynchus anatinus) that reached Britain in the late 18th century was regarded a scientific hoax. Over decades the anatomical characteristics of these unique mammals, such as egg laying and the existence of mammary glands, were hotly debated before they were accepted. Within the last 40 years, more and more details of monotreme physiology, histology, reproduction and genetics have been revealed. Some show similarities with birds or reptiles, some with therian mammals, but many are very specific to monotremes. The genome is no exception to monotreme uniqueness. An early opinion was that the karyotype, composed of a few large chromosomes and many small ones, resembled bird and reptile macro- and micro-chromosomes. However, the platypus genome also features characteristics that are not present in other mammals, such as a complex translocation system. The sex chromosome system is still not resolved. Nothing is known about dosage compensation and, unlike in therian mammals, there seems to be no genomic imprinting. In this article we will recount the mysteries of the monotreme genome and describe how we are using recently developed technology to identify chromosomes in mitosis, meiosis and sperm, to map genes to chromosomes, to unravel the sex chromosome system and the translocation chain and investigate X inactivation and genomic imprinting in monotremes.

Animals↗
PubMed2004

Making the right choice--long-range chromosomal interactions in development.

Schizosaccharomyces pombe has the remarkable potential to switch mating type as often as every generation, through selective interaction of an expressor locus with either of two transcriptionally silent donor loci. Recent results demonstrate that selection of the appropriate donor locus likely occurs through mating-type and heterochromatin-dependent spreading of a protein complex that marks the correct donor locus.

Chromosomes↗
PubMed2003

Status and future direction of male contraceptive development.

Control of fertility constitutes a global health issue, as overpopulation and unintended pregnancy have both major personal and societal impact. Although the contraceptive revolution in the 1960s following the development of hormonal-based oral contraceptives for women has had a major impact on societal dynamics in several cultures, little product innovation has occurred since then. One solution to this global health issue lies in the development of new and innovative contraceptives for both women and men, the goal of which is to provide a range of options for people at all stages and walks of life. Currently, three options for male-based contraception exist (i.e. withdrawal, condoms and vasectomy), and these are acknowledged as woefully inadequate. Introduction of new forms of male contraception based on both hormonal and non-hormonal paradigms are wanted and needed; this need is now becoming recognized by both the public and private sectors. New and innovative products will come from our knowledge of the unique physiology and genetics of reproduction, as well as by exploiting existing and future genomics, proteomics and protein network platforms.

Contraceptive Agents, Male↗