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Topic Review
Interspecific and Intergeneric Hybridization
Interspecific hybridization occurs when crosses are made between different cultivated species belonging to the same genus. In contrast, the outcome of the combination of a distinct genus (cultivated species with their wild relatives) is known as intergeneric hybridization. These two approaches are the critical driving force in generating a different combination of hybrid lines, such as synthetic amphiploid lines, alloplasmic lines, and alien gene introgression lines, which act as a source of variation that leads to a broadening of the genetic variability and diversity of desired traits for crop improvement. However, the success rate of interspecific and intergeneric hybridization is comparatively low compared to intraspecific hybridization due to cross-incompatibilities mainly related to pre- and post-fertilization barriers. To overcome these challenges, in vitro techniques utilizing somatic hybridization or embryo rescue came into the picture and have proven to be the best alternative. Several embryo rescue techniques such as embryo culture, ovary culture, ovule culture, anther culture, and protoplast culture protect embryos from successful hybridization and from premature abortion. Due to the genomic shock, this successful hybridization induces genetic and epigenetic modification at the early stages (zygote formation and development) of hybrids and successive generations. Embryo rescue techniques such as immature embryo culture were used to develop an interspecific hybrid ACC between B. napus ‘Zhongshuang 9’ and B. oleracea ‘6m08.
  • 9.2K
  • 16 Sep 2022
Topic Review
Anaphase Bridges
Anaphase bridges are DNA threads stretching between the two DNA masses as cells attempt to segregate them during anaphase. Anaphase bridges arise from unresolved DNA intertwines between sister chromatids. Sister chromatid intertwines (SCIs) naturally arise during DNA replication and represent a non-proteinaceous source of cohesion between sister chromatids. SCIs and are mainly resolved in S phase, although some do persist and must be fully removed during mitosis to allow faithful chromosome segregation and avoid the arising of DNA lesions and genome instability, a hallmark of cancer development. As complete resolution of SCIs only occurs during chromosome segregation, it is not clear whether intertwines that persist in mitosis are simply an unwanted leftover or whether they have a functional role.
  • 8.1K
  • 04 Sep 2020
Topic Review
48,XXYY Syndrome
48,XXYY syndrome is a chromosomal condition that causes infertility, developmental and behavioral disorders, and other health problems in males.
  • 4.9K
  • 23 Dec 2020
Topic Review
48,XXXY Syndrome
48,XXXY syndrome is a chromosomal condition in boys and men that causes intellectual disability, developmental delays, physical differences, and an inability to father biological children (infertility). Its signs and symptoms vary among affected individuals.
  • 4.8K
  • 23 Dec 2020
Topic Review
Mesoamerican Genetic Studies
Mesoamerica is a historically and culturally defined geographic area comprising current central and south Mexico, Belize, Guatemala, El Salvador, and border regions of Honduras, western Nicaragua, and northwestern Costa Rica. The permanent settling of Mesoamerica was accompanied by the development of agriculture and pottery manufacturing (2500 BCE–150 CE), which led to the rise of several cultures connected by commerce and farming. Hence, Mesoamericans probably carried an invaluable genetic diversity partly lost during the Spanish conquest and the subsequent colonial period. Mesoamerican ancient DNA (aDNA) research has mainly focused on the study of mitochondrial DNA in the Basin of Mexico and the Yucatán Peninsula and its nearby territories, particularly during the Postclassic period (900–1519 CE). 
  • 4.7K
  • 24 Nov 2020
Topic Review
Hybrid
In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are. Species are reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes. A few animal species and many plant species, however, are the result of hybrid speciation, including important crop plants such as wheat, where the number of chromosomes has been doubled. Human impact on the environment has resulted in an increase in the interbreeding between regional species, and the proliferation of introduced species worldwide has also resulted in an increase in hybridisation. This genetic mixing may threaten many species with extinction, while genetic erosion from monoculture in crop plants may be damaging the gene pools of many species for future breeding. A form of often intentional human-mediated hybridisation is the crossing of wild and domesticated species. This is common in both traditional horticulture and modern agriculture; many commercially useful fruits, flowers, garden herbs, and trees have been produced by hybridisation. One such flower, Oenothera lamarckiana, was central to early genetics research into mutationism and polyploidy. It is also more occasionally done in the livestock and pet trades; some well-known wild × domestic hybrids are beefalo and wolfdogs. Human selective breeding of domesticated animals and plants has resulted in the development of distinct breeds (usually called cultivars in reference to plants); crossbreeds between them (without any wild stock) are sometimes also imprecisely referred to as "hybrids". Hybrid humans existed in prehistory. For example, Neanderthals and anatomically modern humans are thought to have interbred as recently as 40,000 years ago. Mythological hybrids appear in human culture in forms as diverse as the Minotaur, blends of animals, humans and mythical beasts such as centaurs and sphinxes, and the Nephilim of the Biblical apocrypha described as the wicked sons of fallen angels and attractive women.
  • 4.3K
  • 24 Nov 2022
Topic Review
Molecular Mechanisms of Homologous Recombination
Homologous recombination (HR) is a fundamental evolutionarily conserved process that plays prime role(s) in genome stability maintenance through DNA repair and through the protection and resumption of arrested replication forks. HR promotes the exchange between homologous DNA sequences resulting in a novel combination of the genetic material. Therefore, HR is essential in genome stability maintenance but also plays an important role in genome diversity; such as in the case of meiosis. Many HR genes are deregulated in cancer cells. Notably, the breast cancer genes BRCA1 and BRCA2, two important HR players, are the most frequently mutated genes in familial breast and ovarian cancer. 
  • 4.3K
  • 28 Apr 2021
Topic Review
Dosage Compensation
Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. Across species, different sexes are often characterized by different types and numbers of sex chromosomes. In order to neutralize the large difference in gene dosage produced by differing numbers of sex chromosomes among the sexes, various evolutionary branches have acquired various methods to equalize gene expression among the sexes. Because sex chromosomes contain different numbers of genes, different species of organisms have developed different mechanisms to cope with this inequality. Replicating the actual gene is impossible; thus organisms instead equalize the expression from each gene. For example, in humans, females (XX) silence the transcription of one X chromosome of each pair, and transcribe all information from the other, expressed X chromosome. Thus, human females have the same number of expressed X-linked genes as do human males (XY), both sexes having essentially one X chromosome per cell, from which to transcribe and express genes. There are three main mechanisms of achieving dosage compensation which are widely documented in the literature and which are common to most species. These include random inactivation of one female X chromosome (as observed in Mus musculus; this is called X-inactivation), a two-fold increase in the transcription of a single male X chromosome (as observed in Drosophila melanogaster), and decreased transcription by half in both of the X chromosomes of a hermaphroditic organism (as observed in Caenorhabditis elegans). These mechanisms have been widely studied and manipulated in model organisms commonly used in the laboratory research setting. A summary of these forms of dosage compensation is illustrated below. However, there are also other less common forms of dosage compensation, which are not as widely researched and are sometimes specific to only one species (as observed in certain bird and monotreme species).
  • 4.1K
  • 31 Oct 2022
Topic Review
Homology
In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales and the forelegs of four-legged vertebrates like dogs and crocodiles are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor. The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this, from Aristotle onwards, and it was explicitly analysed by Pierre Belon in 1555. In developmental biology, organs that developed in the embryo in the same manner and from similar origins, such as from matching primordia in successive segments of the same animal, are serially homologous. Examples include the legs of a centipede, the maxillary palp and labial palp of an insect, and the spinous processes of successive vertebrae in a vertebral column. Male and female reproductive organs are homologous if they develop from the same embryonic tissue, as do the ovaries and testicles of mammals including humans. Sequence homology between protein or DNA sequences is similarly defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either a speciation event (orthologs) or a duplication event (paralogs). Homology among proteins or DNA is inferred from their sequence similarity. Significant similarity is strong evidence that two sequences are related by divergent evolution from a common ancestor. Alignments of multiple sequences are used to discover the homologous regions. Homology remains controversial in animal behaviour, but there is suggestive evidence that, for example, dominance hierarchies are homologous across the primates.
  • 3.9K
  • 10 Oct 2022
Topic Review
F13A1 Gene
Coagulation factor XIII A chain
  • 3.9K
  • 24 Dec 2020
Topic Review
SRY Gene
SRY: Sex determining region Y. The SRY gene provides instructions for making a protein called the sex-determining region Y protein.
  • 3.9K
  • 22 Dec 2020
Topic Review
Action Myoclonus–Renal Failure Syndrome
Action myoclonus–renal failure (AMRF) syndrome causes episodes of involuntary muscle jerking or twitching (myoclonus) and, often, kidney (renal) disease. Although the condition name refers to kidney disease, not everyone with the condition has problems with kidney function.
  • 3.8K
  • 23 Dec 2020
Topic Review
49,XXXXY Syndrome
49,XXXXY syndrome is a chromosomal condition in boys and men that causes intellectual disability, developmental delays, physical differences, and an inability to father biological children (infertility). Its signs and symptoms vary among affected individuals.
  • 3.8K
  • 23 Dec 2020
Topic Review
Gene Therapy
Gene therapy is an experimental technique that uses genes to treat or prevent disease. 
  • 3.6K
  • 24 Dec 2020
Topic Review
Premature Termination Codons
Premature termination codons (PTCs) are stop codons arising from nonsense variants converting a sense codon into a termination signal, i.e. UAA, UAG or UGA. PTCs arising from mutations may, at low frequency, be misrecognized and result in PTC suppression, named ribosome readthrough, with production of full-length proteins through the insertion of a subset of amino acids. Since some drugs have been identified as readthrough inducers, this fidelity drawback has been explored as a therapeutic approach in several models of human diseases caused by nonsense mutations.
  • 3.3K
  • 23 Dec 2020
Topic Review
DNA Barcoding
DNA barcoding is a method of species identification using a short section of DNA from a specific gene or genes. The premise of DNA barcoding is that, by comparison with a reference library of such DNA sections (also called "sequences"), an individual sequence can be used to uniquely identify an organism to species, in the same way that a supermarket scanner uses the familiar black stripes of the UPC barcode to identify an item in its stock against its reference database. These "barcodes" are sometimes used in an effort to identify unknown species, parts of an organism, or simply to catalog as many taxa as possible, or to compare with traditional taxonomy in an effort to determine species boundaries. Different gene regions are used to identify the different organismal groups using barcoding. The most commonly used barcode region for animals and some protists is a portion of the cytochrome c oxidase I (COI or COX1) gene, found in mitochondrial DNA. Other genes suitable for DNA barcoding are the internal transcribed spacer (ITS) rRNA often used for fungi and RuBisCO used for plants. Microorganisms are detected using different gene regions. The 16S rRNA gene for example is widely used in identification of prokaryotes, whereas the 18S rRNA gene is mostly used for detecting microbial eukaryotes. These gene regions are chosen because they have less intraspecific (within species) variation than interspecific (between species) variation, which is known as the "Barcoding Gap". Some applications of DNA barcoding include: identifying plant leaves even when flowers or fruits are not available; identifying pollen collected on the bodies of pollinating animals; identifying insect larvae which may have fewer diagnostic characters than adults; or investigating the diet of an animal based on its stomach content, saliva or feces. When barcoding is used to identify organisms from a sample containing DNA from more than one organism, the term DNA metabarcoding is used, e.g. DNA metabarcoding of diatom communities in rivers and streams, which is used to assess water quality.
  • 3.2K
  • 16 Nov 2022
Topic Review
Snijders Blok-Campeau Syndrome
Snijders Blok-Campeau syndrome is characterized by intellectual disability, speech problems, and distinctive facial features.  
  • 3.1K
  • 23 Dec 2020
Topic Review
3p Deletion Syndrome
3p deletion syndrome is a condition that results from a chromosomal change in which a small piece of chromosome 3 is deleted in each cell. The deletion occurs at the end of the short (p) arm of the chromosome. This chromosomal change often leads to intellectual disability, developmental delay, and abnormal physical features.
  • 2.8K
  • 23 Dec 2020
Topic Review
NRF2
Nuclear factor erythroid 2‐related factor 2 (NRF2) is a transcription factor that regulates the cellular defense against toxic and oxidative insults through the expression of genes involved in oxidative stress response and drug detoxification. NRF2 activation renders cells resistant to chemical carcinogens and inflammatory challenges. In addition to antioxidant responses, NRF2 is involved in other cellular processes, including metabolism and inflammation, and its functions are beyond the originally envisioned. NRF2 activity is tightly regulated through a complex transcriptional and post-translational network that enables it to orchestrate the cell’s response and adaptation to various pathological stressors for the homeostasis maintenance. Elevated or decreased NRF2 activity by pharmacological and genetic manipulations of NRF2 activation is associated with many metabolism- or inflammation-related diseases. Emerging evidence shows that NRF2 lies at the center of a complex regulatory network and establishes NRF2 as a truly pleiotropic transcription factor. Here we summarize the complex regulatory network of NRF2 activity and its roles in metabolic reprogramming, unfolded protein response, proteostatsis, autophagy, mitochondrial biogenesis, inflammation, and immunity.
  • 2.6K
  • 17 Jul 2020
Topic Review
Human Genetic Clustering
Human genetic clustering is the degree to which human genetic variation can be partitioned into a small number of groups or clusters. A leading method of analysis uses mathematical cluster analysis of the degree of similarity of genetic data between individuals and groups in order to infer population structures and assign individuals to hypothesized ancestral groups. A similar analysis can be done using principal component analysis, and several recent studies deploy both methods. Analysis of genetic clustering examines the degree to which regional groups differ genetically, the categorization of individuals into clusters, and what can be learned about human ancestry from this data. There is broad scientific agreement that a relatively small fraction of human genetic variation occurs between populations, continents, or clusters. Researchers of genetic clustering differ, however, on whether genetic variation is principally clinal or whether clusters inferred mathematically are important and scientifically useful.
  • 2.6K
  • 23 Nov 2022
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