Ploidy is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here sets of chromosomes refers to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair—the form in which chromosomes naturally exist. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present : monoploid, diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid or septaploid, etc. The generic term polyploid is often used to describe cells with three or more sets of chromosomes.
Polyploidy is a condition in which the cells of an organism have more than two paired sets of (homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one from each of two parents; each set contains the same number of chromosomes, and the chromosomes are joined in pairs of homologous chromosomes. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis; the sporophyte generation is diploid and produces spores by meiosis.
Arachnids are arthropods in the class Arachnida of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.
In cellular biology, a somatic cell, or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Somatic cells compose the body of an organism and divide through mitosis.
Uloboridae is a family of non-venomous spiders, known as cribellate orb weavers or hackled orb weavers. Their lack of venom glands is a secondarily evolved trait. Instead, they wrap their prey thoroughly in silk, cover it in regurgitated digestive enzymes, and then ingest the liquified body.
Gene duplication is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.
In genetics and bioinformatics, a single-nucleotide polymorphism is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population, many publications do not apply such a frequency threshold.
The origin of replication is a particular sequence in a genome at which replication is initiated. Propagation of the genetic material between generations requires timely and accurate duplication of DNA by semiconservative replication prior to cell division to ensure each daughter cell receives the full complement of chromosomes. This can either involve the replication of DNA in living organisms such as prokaryotes and eukaryotes, or that of DNA or RNA in viruses, such as double-stranded RNA viruses. Synthesis of daughter strands starts at discrete sites, termed replication origins, and proceeds in a bidirectional manner until all genomic DNA is replicated. Despite the fundamental nature of these events, organisms have evolved surprisingly divergent strategies that control replication onset. Although the specific replication origin organization structure and recognition varies from species to species, some common characteristics are shared.
Comparative genomics is a branch of biological research that examines genome sequences across a spectrum of species, spanning from humans and mice to a diverse array of organisms from bacteria to chimpanzees. This large-scale holistic approach compares two or more genomes to discover the similarities and differences between the genomes and to study the biology of the individual genomes. Comparison of whole genome sequences provides a highly detailed view of how organisms are related to each other at the gene level. By comparing whole genome sequences, researchers gain insights into genetic relationships between organisms and study evolutionary changes. The major principle of comparative genomics is that common features of two organisms will often be encoded within the DNA that is evolutionarily conserved between them. Therefore, Comparative genomics provides a powerful tool for studying evolutionary changes among organisms, helping to identify genes that are conserved or common among species, as well as genes that give unique characteristics of each organism. Moreover, these studies can be performed at different levels of the genomes to obtain multiple perspectives about the organisms.
Streptomyces is the largest genus of Actinomycetota, and the type genus of the family Streptomycetaceae. Over 700 species of Streptomyces bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positive, and have very large genomes with high GC content. Found predominantly in soil and decaying vegetation, most streptomycetes produce spores, and are noted for their distinct "earthy" odor that results from production of a volatile metabolite, geosmin. Different strains of the same species may colonize very diverse environments.
A nuclear gene is a gene that has its DNA nucleotide sequence physically situated within the cell nucleus of a eukaryotic organism. This term is employed to differentiate nuclear genes, which are located in the cell nucleus, from genes that are found in mitochondria or chloroplasts. The vast majority of genes in eukaryotes are nuclear.
The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects, the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons. It is also present in some plants, where it has probably evolved independently on several occasions. The letters Z and W are used to distinguish this system from the XY sex-determination system. In the ZW system, females have a pair of dissimilar ZW chromosomes, and males have two similar ZZ chromosomes.
A spider web, spiderweb, spider's web, or cobweb is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey.
A reference genome is a digital nucleic acid sequence database, assembled by scientists as a representative example of the set of genes in one idealized individual organism of a species. As they are assembled from the sequencing of DNA from a number of individual donors, reference genomes do not accurately represent the set of genes of any single individual organism. Instead, a reference provides a haploid mosaic of different DNA sequences from each donor. For example, one of the most recent human reference genomes, assembly GRCh38/hg38, is derived from >60 genomic clone libraries. There are reference genomes for multiple species of viruses, bacteria, fungus, plants, and animals. Reference genomes are typically used as a guide on which new genomes are built, enabling them to be assembled much more quickly and cheaply than the initial Human Genome Project. Reference genomes can be accessed online at several locations, using dedicated browsers such as Ensembl or UCSC Genome Browser.
Diaphorina citri, the Asian citrus psyllid, is a sap-sucking, hemipteran bug now in the taxonomic family Psyllidae. It is one of two confirmed vectors of citrus greening disease. It has a wide distribution in southern Asia and has spread to other citrus growing regions.
Latrodectus elegans is a species of black widow spider, found in South Asia, Southeast Asia and East Asia. It was first collected by the Swedish arachnologist Tamerlan Thorell in the Karen Hills in Myanmar, but is also found in Thailand, India, Nepal, Vietnam, China and Japan. As of July 2022, the World Spider Catalog lists only India, Nepal, Myanmar, China and Japan. This species has been recorded in India and Nepal only since 2012, and Indochina in 2015, which is thought to reflect historical under-surveying of arachnids in this region.
Nuclear organization refers to the spatial organization and dynamics of chromatin within a cell nucleus during interphase. There are many different levels and scales of nuclear organisation.
Uloborus campestratus is a species of cribellate orb weaver in the spider family Uloboridae. It is found in a range from the United States to Venezuela.
