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Mutagenesis is a process by which the genetic information of an organism is changed by the production of a mutation. It may occur spontaneously in nature,or as a result of exposure to mutagens. It can also be achieved experimentally using laboratory procedures. A mutagen is a mutation-causing agent,be it chemical or physical,which results in an increased rate of mutations in an organism's genetic code. In nature mutagenesis can lead to cancer and various heritable diseases,and it is also a driving force of evolution. Mutagenesis as a science was developed based on work done by Hermann Muller,Charlotte Auerbach and J. M. Robson in the first half of the 20th century.
Chromosomal crossover,or crossing over,is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes. It is one of the final phases of genetic recombination,which occurs in the pachytene stage of prophase I of meiosis during a process called synapsis. Synapsis begins before the synaptonemal complex develops and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.
Saccharomyces cerevisiae is a species of yeast. The species has been instrumental in winemaking,baking,and brewing since ancient times. It is believed to have been originally isolated from the skin of grapes. It is one of the most intensively studied eukaryotic model organisms in molecular and cell biology,much like Escherichia coli as the model bacterium. It is the microorganism behind the most common type of fermentation. S. cerevisiae cells are round to ovoid,5–10 μm in diameter. It reproduces by budding.
Franklin (Frank) William Stahl is an American molecular biologist and geneticist. With Matthew Meselson,Stahl conducted the famous Meselson-Stahl experiment showing that DNA is replicated by a semiconservative mechanism,meaning that each strand of the DNA serves as a template for production of a new strand.
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids. It is widely used by cells to accurately repair harmful breaks that occur on both strands of DNA,known as double-strand breaks (DSB),in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis,the process by which eukaryotes make gamete cells,like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring,which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses.
A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome,with both copies joined together by a common centromere. In other words,a sister chromatid may also be said to be 'one-half' of the duplicated chromosome. A pair of sister chromatids is called a dyad. A full set of sister chromatids is created during the synthesis (S) phase of interphase,when all the chromosomes in a cell are replicated. The two sister chromatids are separated from each other into two different cells during mitosis or during the second division of meiosis.
A Holliday junction is a branched nucleic acid structure that contains four double-stranded arms joined. These arms may adopt one of several conformations depending on buffer salt concentrations and the sequence of nucleobases closest to the junction. The structure is named after Robin Holliday,the molecular biologist who proposed its existence in 1964.
Mitotic recombination is a type of genetic recombination that may occur in somatic cells during their preparation for mitosis in both sexual and asexual organisms. In asexual organisms,the study of mitotic recombination is one way to understand genetic linkage because it is the only source of recombination within an individual. Additionally,mitotic recombination can result in the expression of recessive genes in an otherwise heterozygous individual. This expression has important implications for the study of tumorigenesis and lethal recessive genes. Mitotic homologous recombination occurs mainly between sister chromatids subsequent to replication. Inter-sister homologous recombination is ordinarily genetically silent. During mitosis the incidence of recombination between non-sister homologous chromatids is only about 1% of that between sister chromatids.
Sister chromatid exchange (SCE) is the exchange of genetic material between two identical sister chromatids.
Postreplication repair is the repair of damage to the DNA that takes place after replication.
SAE2 is a gene in budding yeast,coding for the protein Sae2,which is involved in DNA repair. Sae2 is a part of the homologous recombination process in response to double-strand breaks. It is best characterized in the yeast model organism Saccharomyces cerevisiae. Homologous genes in other organisms include Ctp1 in fission yeast,Com1 in plants,and CtIP in higher eukaryotes including humans.
Homology-directed repair (HDR) is a mechanism in cells to repair double-strand DNA lesions. The most common form of HDR is homologous recombination. The HDR mechanism can only be used by the cell when there is a homologous piece of DNA present in the nucleus,mostly in G2 and S phase of the cell cycle. Other examples of homology-directed repair include single-strand annealing and breakage-induced replication. When the homologous DNA is absent,another process called non-homologous end joining (NHEJ) takes place instead.
Virginia Zakian is the Harry C. Wiess Professor in the Life Sciences in the Department of Molecular Biology at Princeton University. She is the director of the Zakian Lab,which has done important research in topics such as telomere-binding protein,telomere recombination,and telomere position effects,at Princeton University. She is a fellow at the American Academy of Microbiology and the American Association for the Advancement of Science.,and is an elected member of the National Academy of Sciences (2018). Zakian served as the chair of "Princeton's Task force on the Status of Women Faculty in the Natural Sciences and Engineering at Princeton" from 2001-2003,in 2003 Zakian became Princeton University's representative to Nine Universities,Gender Equity Analysis She was elected as a member of the American Academy of Arts and Sciences in 2019.
The meiotic recombination checkpoint monitors meiotic recombination during meiosis,and blocks the entry into metaphase I if recombination is not efficiently processed.
The origin and function of meiosis are currently not well understood scientifically,and would provide fundamental insight into the evolution of sexual reproduction in eukaryotes. There is no current consensus among biologists on the questions of how sex in eukaryotes arose in evolution,what basic function sexual reproduction serves,and why it is maintained,given the basic two-fold cost of sex. It is clear that it evolved over 1.2 billion years ago,and that almost all species which are descendants of the original sexually reproducing species are still sexual reproducers,including plants,fungi,and animals.
Synthesis-dependent strand annealing (SDSA) is a major mechanism of homology-directed repair of DNA double-strand breaks (DSBs). Although many of the features of SDSA were first suggested in 1976,the double-Holliday junction model proposed in 1983 was favored by many researchers. In 1994,studies of double-strand gap repair in Drosophila were found to be incompatible with the double-Holliday junction model,leading researchers to propose a model they called synthesis-dependent strand annealing. Subsequent studies of meiotic recombination in S. cerevisiae found that non-crossover products appear earlier than double-Holliday junctions or crossover products,challenging the previous notion that both crossover and non-crossover products are produced by double-Holliday junctions and leading the authors to propose that non-crossover products are generated through SDSA.
Leona D. Samson is the Uncas and Helen Whitaker Professor and American Cancer Society Research Professor of Biological Engineering at the Massachusetts Institute of Technology,where she served as the Director of the Center for Environmental Health Sciences from 2001 to 2012. Before her professorship at MIT,she held a professorship at the Harvard School of Public Health. She is on the editorial board of the journal DNA Repair. Her research interests focus on "methods for measuring DNA repair capacity (DRC) in human cells",research the National Institute of Health recognized as pioneering in her field,for which the NIH granted her the National Institutes of Health Director's Pioneer Award.
Fred Sherman was an American scientist who pioneered the use of the budding yeast Saccharomyces cerevisiae as a model for studying the genetics,molecular biology,and biochemistry of eukaryotic cells. His research encompassed broad areas of yeast biology including gene expression,protein synthesis,messenger RNA processing,bioenergetics,and mechanisms of mutagenesis. He also contributed extensively to the genetics of the opportunistic pathogen Candida albicans.
Sue Jinks-Robertson is an American professor of genetics and microbiology. She is currently a professor in the Department of Molecular Genetics and Microbiology at the Duke University School of Medicine. In May 2019,she was elected to the National Academy of Sciences. She has published over 100 scientific articles in peer-reviewed journals.
Bernard Dujon is a French geneticist,born on August 8,1947 in Meudon (Hauts-de-Seine). He is Professor Emeritus at Sorbonne University and the Institut Pasteur since 2015. He is a member of the French Academy of sciences.
References
- 1 2 "Mechanisms of Homologous Recombination". mendellectures.muni.cz. Retrieved March 15, 2021.
- ↑ Lee, Andrew H.; Symington, Lorraine S.; Fidock, David A. (September 7, 2014). "DNA Repair Mechanisms and Their Biological Roles in the Malaria Parasite Plasmodium falciparum". Microbiology and Molecular Biology Reviews . 78 (3): 469–486. doi: 10.1128/MMBR.00059-13 . PMC 4187680 . PMID 25184562.
- ↑ "Lorraine Symington Elected to American Academy of Arts and Sciences". cuimc.columbia.edu. April 23, 2018. Retrieved March 15, 2021.
- ↑ "Five Columbia Faculty Join the Ranks of the National Academy of Sciences". news.columbia.edu. March 2, 2020. Retrieved March 15, 2021.
