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65-398: Lake Fryxell is 20 metres (66 ft) deep, so that the deepest portion of the lake is below sea level. The lake is dammed by Canada Glacier, so that it has no natural outflow. It is covered with about 4.5 metres (15 ft) of ice, but during the summer months, the ice can clear along the shoreline. There are a few small islands as well as several shallow areas. The average annual ablation

130-429: A DNA sequence may be useful in practically any biological research . For example, in medicine it can be used to identify, diagnose and potentially develop treatments for genetic diseases . Similarly, research into pathogens may lead to treatments for contagious diseases. Biotechnology is a burgeoning discipline, with the potential for many useful products and services. RNA is not sequenced directly. Instead, it

195-460: A chain of linked units called nucleotides. Each nucleotide consists of three subunits: a phosphate group and a sugar ( ribose in the case of RNA , deoxyribose in DNA ) make up the backbone of the nucleic acid strand, and attached to the sugar is one of a set of nucleobases . The nucleobases are important in base pairing of strands to form higher-level secondary and tertiary structures such as

260-628: A few archaea living in the anoxic zone, that contribute to the methane pockets under 12 m below the surface. There is a lack of oxygen within Lake Fryxell, which is unique when compared to other lakes in the region because the euphotic zone only extends to 9 metres (30 ft) below the lake surface. This creates an environment similar to the planet about 2.4 billion years ago. Within anoxic areas, scientists have found microbial mats that create small pockets saturated with oxygen. Ablation#Glaciology Ablation ( Latin : ablatio – removal)

325-410: A glacier or snowfield. Ablation refers to the melting of snow or ice that runs off the glacier, evaporation , sublimation , calving , or erosive removal of snow by wind. Air temperature is typically the dominant control of ablation, with precipitation exercising secondary control. In a temperate climate during ablation season, ablation rates typically average around 2 mm/h. Where solar radiation

390-481: A high degree of target specificity. The genetic ablation techniques described could prove useful in battling cancer. Electro-ablation , is a process that removes material from a metallic workpiece to reduce surface roughness . Electro-ablation breaks through highly resistive oxide surfaces, such as those found on titanium and other exotic metals and alloys without melting the underlying non-oxidised metal or alloy. This allows very quick surface finishing The process

455-468: A house. There have been many experiments done to demonstrate the effect of debris on the surface of glaciers. Yoshiyuki Fujii, a professor at the National Institute of Polar Research , designed an experiment that showed ablation rate was accelerated under a thin debris layer and was retarded under a thick one as compared with that of a natural snow surface. This science is significant due to

520-495: A minimum absorption depth. While these lasers can average a low power, they can offer peak intensity and fluence given by: while the peak power is Surface ablation of the cornea for several types of eye refractive surgery is now common, using an excimer laser system ( LASIK and LASEK ). Since the cornea does not grow back, laser is used to remodel the cornea refractive properties to correct refraction errors , such as astigmatism , myopia , and hyperopia . Laser ablation

585-486: A population or culture are destroyed or removed. Both can be used as experimental tools, as in loss-of-function experiments. In medicine, ablation is the removal of a part of biological tissue , usually by surgery . Surface ablation of the skin ( dermabrasion , also called resurfacing because it induces regeneration ) can be carried out by chemicals (chemoablation), by lasers ( laser ablation ), by freezing ( cryoablation ), or by electricity ( fulguration ). Its purpose

650-481: A protoplanetary disk would result in significant ablation of the disk, and this ablation would strip a significant amount of protoplanetary material from the disk – but not necessarily destroy the disk entirely. This is an important point because a disk that survives such an interaction with sufficient material leftover to form a planetary system may inherit an altered disk chemistry from the SNR, which could have effects on

715-478: A rough measure of how conserved a particular region or sequence motif is among lineages. The absence of substitutions, or the presence of only very conservative substitutions (that is, the substitution of amino acids whose side chains have similar biochemical properties) in a particular region of the sequence, suggest that this region has structural or functional importance. Although DNA and RNA nucleotide bases are more similar to each other than are amino acids,

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780-425: A sequence is on the coding strand if it has the same order as the transcribed RNA. One sequence can be complementary to another sequence, meaning that they have the base on each position in the complementary (i.e., A to T, C to G) and in the reverse order. For example, the complementary sequence to TTAC is GTAA. If one strand of the double-stranded DNA is considered the sense strand, then the other strand, considered

845-414: A sequence of amino acids making up a protein strand. Each group of three bases, called a codon , corresponds to a single amino acid, and there is a specific genetic code by which each possible combination of three bases corresponds to a specific amino acid. The central dogma of molecular biology outlines the mechanism by which proteins are constructed using information contained in nucleic acids. DNA

910-624: A thymine could occur in that position without impairing the sequence's functionality. These symbols are also valid for RNA, except with U (uracil) replacing T (thymine). Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytidine (m5C). In RNA, there are many modified bases, including pseudouridine (Ψ), dihydrouridine (D), inosine (I), ribothymidine (rT) and 7-methylguanosine (m7G). Hypoxanthine and xanthine are two of

975-430: Is transcribed into mRNA molecules, which travel to the ribosome where the mRNA is used as a template for the construction of the protein strand. Since nucleic acids can bind to molecules with complementary sequences, there is a distinction between " sense " sequences which code for proteins, and the complementary "antisense" sequence, which is by itself nonfunctional, but can bind to the sense strand. DNA sequencing

1040-437: Is a focus of scientific research and contains a semi-permanent camp containing four labs and two other buildings. Electricity is generated at the camp using solar panels and a wind turbine. The four labs are used for experimenting with radioactive materials, electronics, chemicals and other materials. When staying at the camp, researchers sleep in tents, some of which are the same style as those used in some Antarctic expeditions in

1105-451: Is also used to remove part of the uterine wall in women with menstruation and adenomyosis problems in a process called endometrial ablation . Researchers have demonstrated a successful technique for ablating subsurface tumors with minimal thermal damage to surrounding healthy tissue, by using a focused laser beam from an ultra-short pulse diode laser source. Antifouling paints and other related coatings are routinely used to prevent

1170-415: Is believed to contain around 20,000–25,000 genes. In addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases , or mutant forms of genes associated with increased risk of developing genetic disorders. Genetic testing identifies changes in chromosomes, genes, or proteins. Usually, testing

1235-469: Is between 30 centimetres (12 in) and 40 centimetres (16 in), which is significantly lower when compared to other nearby frozen water bodies, such as the waters adjacent to Ross Island . The watershed contains thirteen streams flowing into the lake, forming a watershed that has an area roughly 230 km (89 sq mi) in size. Where a few of the streams enter the lake there are well-developed deltas. The streams flow for about 4–12 weeks out of

1300-443: Is calculated to be sufficient to survive the heat it will encounter on its mission. There is an entire branch of spaceflight research involving the search for new fireproofing materials to achieve the best ablative performance; this function is critical to protect the spacecraft occupants and payload from otherwise excessive heat loading. The same technology is used in some passive fire protection applications, in some cases by

1365-419: Is capable of providing surface finishing for a wide range of exotic and widely used metals and alloys, including: titanium, stainless steel, niobium, chromium–cobalt, Inconel , aluminium, and a range of widely available steels and alloys. Electro-ablation is very effective at achieving high levels of surface finishing in holes, valleys and hidden or internal surfaces on metallic workpieces (parts). The process

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1430-402: Is carried away from the spacecraft by the gases generated by the ablative process, and never penetrates the surface material, so the metallic and other sensitive structures they protect, remain at a safe temperature. As the surface burns and disperses into space, the remaining solid material continues to insulate the craft from ongoing heat and superheated gases. The thickness of the ablative layer

1495-443: Is copied to a DNA by reverse transcriptase , and this DNA is then sequenced. Current sequencing methods rely on the discriminatory ability of DNA polymerases, and therefore can only distinguish four bases. An inosine (created from adenosine during RNA editing ) is read as a G, and 5-methyl-cytosine (created from cytosine by DNA methylation ) is read as a C. With current technology, it is difficult to sequence small amounts of DNA, as

1560-406: Is often used in the context of laser ablation , a process in which a laser dissolves a material's molecular bonds . For a laser to ablate tissues, the power density or fluence must be high, otherwise thermocoagulation occurs, which is simply thermal vaporization of the tissues. Rotablation is a type of arterial cleansing that consists of inserting a tiny, diamond-tipped, drill-like device into

1625-500: Is particularly applicable to components produced by additive manufacturing process, such as 3D-printed metals. These components tend to be produced with roughness levels well above 5–20 micron. Electro-ablation can be used to quickly reduce the surface roughness to less than 0.8 micron, allowing the post-process to be used for volume production surface finishing. In glaciology and meteorology , ablation—the opposite of accumulation—refers to all processes that remove snow, ice, or water from

1690-413: Is potentially a much more efficient method of removing unwanted cells, such as tumor cells, because large numbers of animals lacking specific cells could be generated. Genetically ablated lines can be maintained for a prolonged period of time and shared within the research community. Researchers at Columbia University report of reconstituted caspases combined from C. elegans and humans, which maintain

1755-437: Is qualitatively related to the sequences' evolutionary distance from one another. Roughly speaking, high sequence identity suggests that the sequences in question have a comparatively young most recent common ancestor , while low identity suggests that the divergence is more ancient. This approximation, which reflects the " molecular clock " hypothesis that a roughly constant rate of evolutionary change can be used to extrapolate

1820-405: Is the dominant cause of snow ablation (e.g., if air temperatures are low under clear skies), characteristic ablation textures such as suncups and penitentes may develop on the snow surface. Ablation can refer to mass loss from the upper surface of a glacier or ocean-driven melt and calving on the face of a glacier terminus. Ablation can refer either to the processes removing ice and snow or to

1885-454: Is the process of determining the nucleotide sequence of a given DNA fragment. The sequence of the DNA of a living thing encodes the necessary information for that living thing to survive and reproduce. Therefore, determining the sequence is useful in fundamental research into why and how organisms live, as well as in applied subjects. Because of the importance of DNA to living things, knowledge of

1950-410: Is the removal of a component of an AI system. The term is by analogy with biology: removal of components of an organism. Biological ablation is the removal of a biological structure or functionality. Genetic ablation is another term for gene silencing , in which gene expression is abolished through the alteration or deletion of genetic sequence information. In cell ablation, individual cells in

2015-430: Is the removal or destruction of something from an object by vaporization , chipping, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for ascent and atmospheric reentry , ice and snow in glaciology , biological tissues in medicine and passive fire protection materials. In artificial intelligence (AI), especially machine learning , ablation

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2080-438: Is to put enough of this material in the way of the fire that a level of fire-resistance rating can be maintained, as demonstrated in a fire test . Ablative materials usually have a large concentration of organic matter that is reduced by fire to ashes. In the case of silicone, organic rubber surrounds very finely divided silica dust (up to 380 m of combined surface area of all the dust particles per gram of this dust ). When

2145-541: Is to remove skin spots, aged skin , wrinkles , thus rejuvenating it. Surface ablation is also employed in otolaryngology for several kinds of surgery, such as the one for snoring . Radiofrequency ablation (RFA) is a method of removing aberrant tissue from within the body via minimally invasive procedures, it is used to cure a variety of cardiac arrhythmia such as supraventricular tachycardia , Wolff–Parkinson–White syndrome (WPW), ventricular tachycardia , and more recently as management of atrial fibrillation . The term

2210-548: Is used to find changes that are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder. Several hundred genetic tests are currently in use, and more are being developed. In bioinformatics, a sequence alignment is a way of arranging the sequences of DNA , RNA , or protein to identify regions of similarity that may be due to functional, structural , or evolutionary relationships between

2275-579: The heat of atmospheric reentry and the Kestrel second stage rocket engine designed for exclusive use in an environment of space vacuum since no heat convection is possible. In a basic sense, ablative material is designed so that instead of heat being transmitted into the structure of the spacecraft, only the outer surface of the material bears the majority of the heating effect. The outer surface chars and burns away – but quite slowly, only gradually exposing new fresh protective material beneath. The heat

2340-451: The ablation rate can produce long-lived protection from the deleterious effects of biofouling. Firestopping and fireproofing products can be ablative in nature. This can mean endothermic materials, or merely materials that are sacrificial and become "spent" over time while exposed to fire , such as silicone firestop products. Given sufficient time under fire or heat conditions, these products char away, crumble, and disappear. The idea

2405-399: The affected artery to remove fatty deposits or plaque. The procedure is used in the treatment of coronary heart disease to restore blood flow. Microwave ablation (MWA) is similar to RFA but at higher frequencies of electromagnetic radiation. High-intensity focused ultrasound (HIFU) ablation removes tissue from within the body noninvasively. Bone marrow ablation is a process whereby

2470-498: The antisense strand, will have the complementary sequence to the sense strand. While A, T, C, and G represent a particular nucleotide at a position, there are also letters that represent ambiguity which are used when more than one kind of nucleotide could occur at that position. The rules of the International Union of Pure and Applied Chemistry ( IUPAC ) are as follows: For example, W means that either an adenine or

2535-561: The area surrounding the valley is equivalent to about 3 cm (1.2 in) of rain a year and a mean annual temperature of −20 °C (−4 °F) with summer temperatures getting above freezing. Mapped by the British Antarctic Expedition under Robert Falcon Scott , 1910–13, the lake was visited by Professor T.L. Péwé during Operation Deep Freeze, 1957–58, who named it for Dr. Fritiof M. Fryxell , glacial geologist of Augustana College , Illinois . Lake Fryxell

2600-421: The buildup of microorganisms and other animals, such as barnacles for the bottom hull surfaces of recreational, commercial and military sea vessels. Ablative paints are often utilized for this purpose to prevent the dilution or deactivation of the antifouling agent. Over time, the paint will slowly decompose in the water, exposing fresh antifouling compounds on the surface. Engineering the antifouling agents and

2665-467: The case in certain clusters , e.g. in the Trapezium cluster . Since massive stars tend to collapse through supernovae at the end of their lives, research is now investigating what role the shockwave of such an explosion, and the resulting supernova remnant (SNR), would play if it occurred in the line of fire of a protoplanetary disk. According to computationally modelled simulations, a SNR striking

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2730-568: The colder mid-plane of the disk from dust grains and ices sticking together. These small accretions grow from pebbles to rocks to early baby planets, called planetesimals , then protoplanets , and eventually, full planets . As it is believed that massive stars may play a role in actively triggering star formation (by introducing gravitational instabilities amongst other factors), it is plausible that young, smaller stars with disks may be living relatively nearby to older, more massive stars. This has already been confirmed through observations to be

2795-408: The conservation of base pairs can indicate a similar functional or structural role. Computational phylogenetics makes extensive use of sequence alignments in the construction and interpretation of phylogenetic trees , which are used to classify the evolutionary relationships between homologous genes represented in the genomes of divergent species. The degree to which sequences in a query set differ

2860-515: The early 20th century. There is internet and phone access at the camp. Research activities largely deal with the lake itself and can include scientists diving into the water. The camp has existed since at least 1984. There are multiple forms of algae within the lake, including a sizable population of sulfate-reducing bacteria. Some samples of these bacteria live in very specific areas, such as specific water depths or locations causing them to experience differing physiochemical conditions. There are also

2925-399: The elapsed time since two genes first diverged (that is, the coalescence time), assumes that the effects of mutation and selection are constant across sequence lineages. Therefore, it does not account for possible differences among organisms or species in the rates of DNA repair or the possible functional conservation of specific regions in a sequence. (In the case of nucleotide sequences,

2990-429: The famed double helix . The possible letters are A , C , G , and T , representing the four nucleotide bases of a DNA strand – adenine , cytosine , guanine , thymine – covalently linked to a phosphodiester backbone. In the typical case, the sequences are printed abutting one another without gaps, as in the sequence AAAGTCTGAC, read left to right in the 5' to 3' direction. With regards to transcription ,

3055-430: The glacier body. It is noted that if the slope of a glacier is too high then the debris will continue to move along the glacier to a further location. The sizes and locations of glaciers vary around the world, so depending on the climate and physical geography the varieties of debris can differ. The size and magnitude of the debris is dependent on the area of glacier and can vary from dust-size fragments to blocks as large as

3120-405: The heat digested by the debris-covered area and is calculated. The calculations are dependent on the area and net absorbed heat amounts in regards to the entire debris-covered zones. These types of calculations are done to various glaciers to understand and analyze future patterns of melting. Moraine (glacial debris) is moved by natural processes that allow for down-slope movement of materials on

3185-558: The human bone marrow cells are eliminated in preparation for a bone marrow transplant . This is performed using high-intensity chemotherapy and total body irradiation . As such, it has nothing to do with the vaporization techniques described in the rest of this article. Ablation of brain tissue is used for treating certain neurological disorders , particularly Parkinson's disease , and sometimes for psychiatric disorders as well. Recently, some researchers reported successful results with genetic ablation. In particular, genetic ablation

3250-409: The importance of long-term availability of water resources and assess glacier response to climate change . Natural resource availability is a major drive behind research conducted in regards to the ablation process and overall study of glaciers. Laser ablation is greatly affected by the nature of the material and its ability to absorb energy, therefore the wavelength of the ablation laser should have

3315-419: The many bases created through mutagen presence, both of them through deamination (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine , and xanthine is produced from guanine . Similarly, deamination of cytosine results in uracil . Given the two 10-nucleotide sequences, line them up and compare the differences between them. Calculate the percent difference by taking

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3380-467: The molecular clock hypothesis in its most basic form also discounts the difference in acceptance rates between silent mutations that do not alter the meaning of a given codon and other mutations that result in a different amino acid being incorporated into the protein.) More statistically accurate methods allow the evolutionary rate on each branch of the phylogenetic tree to vary, thus producing better estimates of coalescence times for genes. Frequently

3445-476: The nucleic acid sequence is also termed the primary structure . The sequence represents genetic information . Biological deoxyribonucleic acid represents the information which directs the functions of an organism . Nucleic acids also have a secondary structure and tertiary structure . Primary structure is sometimes mistakenly referred to as "primary sequence". However there is no parallel concept of secondary or tertiary sequence. Nucleic acids consist of

3510-415: The number of differences between the DNA bases divided by the total number of nucleotides. In this case there are three differences in the 10 nucleotide sequence. Thus there is a 30% difference. In biological systems, nucleic acids contain information which is used by a living cell to construct specific proteins . The sequence of nucleobases on a nucleic acid strand is translated by cell machinery into

3575-426: The order of the nucleotides. By convention, sequences are usually presented from the 5' end to the 3' end . For DNA, with its double helix, there are two possible directions for the notated sequence; of these two, the sense strand is used. Because nucleic acids are normally linear (unbranched) polymers , specifying the sequence is equivalent to defining the covalent structure of the entire molecule. For this reason,

3640-411: The organic rubber is exposed to fire, it burns to ash and leaves behind the silica dust with which the product started. Protoplanetary disks are rotating circumstellar disks of dense gas and dust surrounding young, newly formed stars. Shortly after star formation , stars often have leftover surrounding material that is still gravitationally bound to them, forming primitive disks that orbit around

3705-498: The planetary systems that later form. In spacecraft design, ablation is used to both cool and protect mechanical parts and/or payloads that would otherwise be damaged by extremely high temperatures. Two principal applications are heat shields for spacecraft entering a planetary atmosphere from space and cooling of rocket engine nozzles . Examples include the Apollo Command Module that protected astronauts from

3770-666: The primary structure encodes motifs that are of functional importance. Some examples of sequence motifs are: the C/D and H/ACA boxes of snoRNAs , Sm binding site found in spliceosomal RNAs such as U1 , U2 , U4 , U5 , U6 , U12 and U3 , the Shine-Dalgarno sequence , the Kozak consensus sequence and the RNA polymerase III terminator . In bioinformatics , a sequence entropy, also known as sequence complexity or information profile,

3835-447: The quantity of ice and snow removed. Debris-covered glaciers have also been shown to greatly impact the ablation process. There is a thin debris layer that can be located on the top of glaciers that intensifies the ablation process below the ice. The debris-covered parts of a glacier that is experiencing ablation are sectioned into three categories which include ice cliffs, ponds, and debris. These three sections allow scientists to measure

3900-406: The same vendors, who offer different versions of these fireproofing products, some for aerospace and some for structural fire protection . Genetic sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate

3965-421: The sequences. If two sequences in an alignment share a common ancestor, mismatches can be interpreted as point mutations and gaps as insertion or deletion mutations ( indels ) introduced in one or both lineages in the time since they diverged from one another. In sequence alignments of proteins, the degree of similarity between amino acids occupying a particular position in the sequence can be interpreted as

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4030-485: The signal is too weak to measure. This is overcome by polymerase chain reaction (PCR) amplification. Once a nucleic acid sequence has been obtained from an organism, it is stored in silico in digital format. Digital genetic sequences may be stored in sequence databases , be analyzed (see Sequence analysis below), be digitally altered and be used as templates for creating new actual DNA using artificial gene synthesis . Digital genetic sequences may be analyzed using

4095-532: The star's equator – not too dissimilarly from the rings of Saturn . This occurs because the decrease in the protostellar material's radius during formation increases angular momentum , which means that this remaining material gets whipped into a flattened circumstellar disk around the star. This circumstellar disk may eventually mature into what is referred to as a protoplanetary disk: a disk of gas, dust, ice and other materials from which planetary systems may form. In these disks, orbiting matter starts to accrete in

4160-424: The tools of bioinformatics to attempt to determine its function. The DNA in an organism's genome can be analyzed to diagnose vulnerabilities to inherited diseases , and can also be used to determine a child's paternity (genetic father) or a person's ancestry . Normally, every person carries two variations of every gene , one inherited from their mother, the other inherited from their father. The human genome

4225-529: The year. Nearly half of the water flowing into the lake comes from Canada, Lost Seal, and Von Guerard streams. Lake Fryxell is located within the McMurdo Dry Valleys , which experience an exceptionally dry climate partially due to katabatic winds descending from the nearby mountains. These winds can exceed 320 km/h (200 mph) under certain conditions and can raise the temperature, melting snow and evaporating water. Average precipitation in

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