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{{Short description|Non-technical introduction to the subject of genetics}}{{Use dmy dates|date=June 2015}}{{Introductory article|Genetics}}{{Introduction to genetics glossary}}{{Biology_nav}}{{Introductory science articles}}
| 遺伝学 |
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Genetics is the study of genes and tries to explain what they are and how they work. Genes are how living organisms inherit features or traits from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes. Genetics tries to identify which traits are inherited and to explain how these traits are passed from generation to generation.
遺伝学（いでんがく、英: Genetics）は遺伝子を研究して、遺伝子とは何か、どのように機能するかを説明しようとする学問領域である。
たとえば、子どもが普通に両親に似ているのは、両親から遺伝子を受け継いでいるためである。
遺伝学は、どの形質が遺伝するかを特定し、その形質がどのように世代から世代へと受け継がれるかを解明しようとするものである。
Some traits are part of an organism's physical appearance, such as eye color or height. Other sorts of traits are not easily seen and include blood types or resistance to diseases. Some traits are inherited through genes, which is the reason why tall and thin people tend to have tall and thin children. Other traits come from interactions between genes and the environment, so a child who inherited the tendency of being tall will still be short if poorly nourished. The way our genes and environment interact to produce a trait can be complicated. For example, the chances of somebody dying of cancer or heart disease seems to depend on both their genes and their lifestyle.
また、血液型や病気への抵抗力など、外見からはわからない形質もある。
一部の形質は遺伝子を通じて受け継がれ、背が高く痩（や）せ型の人は、背が高くて痩せ型の子どもを生む傾向がある。
また、遺伝子と環境の相互作用から起こる形質もあり、背が高いという傾向を受け継いだ子どもでも、栄養状態が悪ければと背が低くなることがある。
このように、遺伝子と環境が相互作用して形質を生み出す仕組みは複雑である。
たとえば、誰かががんや心臓病で死亡する確率は、その人の遺伝子と生活習慣の両方に依存していると考えられる。
Genes are made from a long molecule called DNA, which is copied and inherited across generations. DNA is made of simple units that line up in a particular order within it, carrying genetic information. The language used by DNA is called genetic code, which lets organisms read the information in the genes. This information is the instructions for the construction and operation of a living organism.
遺伝子は、DNAと呼ばれる長い分子から作られ、世代を超えて複製されて受け継がれる。
DNAは単純な単位で構成され、特定の順序で並んで遺伝情報を運んでいる。
DNAが使用する言語は遺伝暗号と呼ばれ、生物に遺伝子の情報を読み取らせる。
この情報は、生物の構築と動作に関する命令である。
The information within a particular gene is not always exactly the same between one organism and another, so different copies of a gene do not always give exactly the same instructions. Each unique form of a single gene is called an allele. As an example, one allele for the gene for hair color could instruct the body to produce much pigment, producing black hair, while a different allele of the same gene might give garbled instructions that fail to produce any pigment, giving white hair. Mutations are random changes in genes and can create new alleles. Mutations can also produce new traits, such as when mutations to an allele for black hair produce a new allele for white hair. This appearance of new traits is important in evolution.
特定の遺伝子内の情報は、ある生物と別の生物では必ずしも同一ではなく、したがって遺伝子の異なるコピーが常に全く同じ指示を与えるとは限らない。
ある遺伝子にそれぞれ固有の形式はアレル（allele）と呼ばれる。
たとえば、髪の色に関する遺伝子の1つのアレルが、体内で色素を多く生成するように指示して黒髪を生成する一方で、同じ遺伝子の別のアレルが、色素を生成しないような無意味な指示をして白髪になるかもしれない。
変異とは遺伝子が無作為に変化することで、新しいアレルが生まれることもある。
たとえば、黒髪のアレルに生じた変異が、白髪のアレルを作り出すなどである。
このような新しい形質の出現は進化において重要である。
遺伝子と遺伝/Genes and inheritance
Genes are pieces of DNA that contain information for the synthesis of ribonucleic acids (RNAs) or polypeptides. Genes are inherited as units, with two parents dividing out copies of their genes to their offspring. Humans have two copies of each of their genes, but each egg or sperm cell only gets one of those copies for each gene. An egg and sperm join to form a zygote with a complete set of genes. The resulting offspring has the same number of genes as their parents, but for any gene, one of their two copies comes from their father and one from their mother.
遺伝子はDNAの断片で、リボ核酸（RNA）やポリペプチドを合成するための情報を含んでいる。
遺伝子は単位として継承され、2人の親がそれぞれの遺伝子の複製を子孫に分配する。
人間は各遺伝子の複製を2つ持っているが、卵子や精子は各遺伝子の複製を1つだけしか持っていない。
卵子と精子が結合して、遺伝子の完全な一式を持つ受精卵（接合子とも）が形成する。
その結果、子孫は両親と同じ数の遺伝子を持つことになり、どの遺伝子についても、2つの複製のうち1つは父親から、もう1つは母親から受け継がれる[1]。
組合せ(掛け合わせ?)の例/ Example of mixing
The effects of mixing depend on the types (the alleles) of the gene. If the father has two copies of an allele for red hair, and the mother has two copies for brown hair, all their children get the two alleles that give different instructions, one for red hair and one for brown. The hair color of these children depends on how these alleles work together. If one allele dominates the instructions from another, it is called the dominant allele, and the allele that is overridden is called the recessive allele. In the case of a daughter with alleles for both red and brown hair, brown is dominant and she ends up with brown hair.
組合せの影響は遺伝子の種類（アレル）によって異なる。
父親が赤髪のアレルを2つ持っていて、母親が茶髪のアレルを2つ持っている場合、2人の子供は皆、赤髪と茶髪という異なる指示を与える2つの アレルを受け継ぐ。
これらの子供の髪の色は、これらのアレルがどのように連携するかによって決まる。
一方のアレルの指示が他方のアレルよりも顕性（優先）であれば、それは顕性アレル（けんせい）と呼ばれ、対して、優先されるアレルは潜性アレル（せんせい）と呼ばれる。
赤髪と茶髪の両方のアレルを持っている娘の場合、茶髪が顕性アレルとなり、茶髪になる[2]。
Although the red color allele is still there in this brown-haired girl, it doesn't show. This is a difference between what is seen on the surface (the traits of an organism, called its phenotype) and the genes within the organism (its genotype). In this example, the allele for brown can be called "B" and the allele for red "b". (It is normal to write dominant alleles with capital letters and recessive ones with lower-case letters.) The brown hair daughter has the "brown hair phenotype" but her genotype is Bb, with one copy of the B allele, and one of the b allele.
この茶髪の娘には赤色のアレルがまだ残っているが、それは表われない。
これは、表面に見えるもの（表現型と呼ばれる生物の形質）と生物内の遺伝子（遺伝子型）の違いである。
この例では、茶色のアレルを「B」と呼び、赤のアレルを「b」と呼ぶ。
（一般に、顕性アレルは大文字で、潜性アレルは小文字で表す）。
茶髪の娘は「茶髪の表現型」を持っているが、遺伝型はBbで、Bアレルとbアレルをそれぞれ1コピーずつ持っている。
Now imagine that this woman grows up and has children with a brown-haired man who also has a Bb genotype. Her eggs will be a mixture of two types, one sort containing the B allele, and one sort the b allele. Similarly, her partner will produce a mix of two types of sperm containing one or the other of these two alleles. When the transmitted genes are joined up in their offspring, these children have a chance of getting either brown or red hair, since they could get a genotype of BB = brown hair, Bb = brown hair or bb = red hair. In this generation, there is, therefore, a chance of the recessive allele showing itself in the phenotype of the children—some of them may have red hair like their grandfather.
次に、この女性が成長して、同様にBb遺伝型を持つ茶髪の男性との間に子供をもうけたと仮定する。
彼女の卵子は2種類の型が混ざって、1つはBアレルを含み、もう1つはbアレルを含む。
同様に、彼女のパートナーは、これら2つのアレル遺伝子のどちらか一方を含む2種類の精子を混ざって作られる。
伝達された遺伝子が子孫に結びつくと、これらの子供はBB＝茶髪、Bb＝茶髪、bb＝赤髪の遺伝型を持つ可能性があり、茶髪か赤髪のいずれかになる可能性がある。
したがって、この世代では、潜性アレルが子供の表現型に現れる可能性がある。
その中には祖父のような赤髪の子供もいるかもしれない[2]。
Many traits are inherited in a more complicated way than the example above. This can happen when there are several genes involved, each contributing a small part to the result. Tall people tend to have tall children because their children get a package of many alleles that each contribute a bit to how much they grow. However, there are not clear groups of "short people" and "tall people", like there are groups of people with brown or red hair. This is because of the large number of genes involved; this makes the trait very variable and people are of many different heights. Despite a common misconception, the green/blue eye traits are also inherited in this complex inheritance model. Inheritance can also be complicated when the trait depends on the interaction between genetics and environment. For example, malnutrition does not change traits like eye color, but can stunt growth.
多くの形質は上記の例よりも複雑な仕組みで遺伝 (継承) する。
このようなことは、複数の遺伝子が関与して、少しずつ結果に影響を及ぼす場合に起こることがある。
背の高い人が背の高い子どもを持つ傾向があるのは、子どもが多くの一括したアレルを継承し、それぞれが成長に少しずつ寄与するからである。
ただし、茶髪や赤髪の人々のグループがあるように、「背の低い人」と「背の高い人」という明確なグループは存在しない。
これは、関与する遺伝子の数が多いためである。その結果、この形質は非常に変動しやすく、人々の身長は多様である[3]。
よく誤解されるが、緑色と青色の目の形質もこの複雑な遺伝モデルで遺伝する[4]。
また、形質が遺伝と環境の相互作用に依存する場合、遺伝は複雑になることもある。
たとえば、栄養失調は目の色のような形質を変化させないが、成長を妨げることがある[5]。
遺伝子の働き/ How genes work
遺伝子はタンパク質を作る/ Genes make proteins
The function of genes is to provide the information needed to make molecules called proteins in cells. Cells are the smallest independent parts of organisms: the human body contains about 100 trillion cells, while very small organisms like bacteria are just a single cell. A cell is like a miniature and very complex factory that can make all the parts needed to produce a copy of itself, which happens when cells divide. There is a simple division of labor in cells—genes give instructions and proteins carry out these instructions, tasks like building a new copy of a cell, or repairing the damage. Each type of protein is a specialist that only does one job, so if a cell needs to do something new, it must make a new protein to do this job. Similarly, if a cell needs to do something faster or slower than before, it makes more or less of the protein responsible. Genes tell cells what to do by telling them which proteins to make and in what amounts.
遺伝子の働きは、細胞内でタンパク質と呼ばれる分子を作るために必要な情報を提供することである[1]。
細胞は生物の最小の独立した部分である。人体には約100兆個の細胞からなるが、細菌のような非常に小さな生物はたった一つの細胞しかない。
細胞は小型で非常に複雑な工場のようなもので、細胞が分裂するとき、自分自身の複製を作るために必要なすべての部品を作ることができる。
細胞の内部には単純な分業があり、遺伝子が指示を与え、タンパク質がその指示を実行する。たとえば、新しい細胞を複製したり、損傷を修復したりする[6]。
各種類のタンパク質は一つの仕事だけをこなす専門家なので、細胞が何か新しいことをする必要があるなら、その仕事をするために新しいタンパク質を作らなくてならない。
同様に、細胞が以前より速く、または遅く何かをする必要があれば、その役割を果たすタンパク質の量を増やしたり減らしたりする。
遺伝子は、どのタンパク質をどれだけの量作るかを細胞に指示することで、細胞に何をすべきかを伝える。
Proteins are made of a chain of 20 different types of amino acid molecules. This chain folds up into a compact shape, rather like an untidy ball of string. The shape of the protein is determined by the sequence of amino acids along its chain and it is this shape that, in turn, determines what the protein does. For example, some proteins have parts of their surface that perfectly match the shape of another molecule, allowing the protein to bind to this molecule very tightly. Other proteins are enzymes, which are like tiny machines that alter other molecules.
タンパク質は20種類のアミノ酸分子の鎖でできている。
この鎖は、乱雑な毛玉のように、密な形状に折りたたまれる。
タンパク質の形状は、その鎖に沿ったアミノ酸の配列によって決まり、この形状によってタンパク質の働きが決定される[6]。
たとえば、あるタンパク質は表面の一部が他の分子の形状と完全に一致し、タンパク質はその分子と非常に強く結合できる。
酵素と呼ばれるタンパク質は、他の分子を変化させる小さな機械のようなものである[7]。
The information in DNA is held in the sequence of the repeating units along the DNA chain. These units are four types of nucleotides (A, T, G and C) and the sequence of nucleotides stores information in an alphabet called the genetic code. When a gene is read by a cell the DNA sequence is copied into a very similar molecule called RNA (this process is called transcription). Transcription is controlled by other DNA sequences (such as promoters), which show a cell where genes are, and control how often they are copied. The RNA copy made from a gene is then fed through a structure called a ribosome, which translates the sequence of nucleotides in the RNA into the correct sequence of amino acids and joins these amino acids together to make a complete protein chain. The new protein then folds up into its active form. The process of moving information from the language of RNA into the language of amino acids is called translation.
DNAの情報は、DNA鎖に沿った反復単位の配列として保持されている[8]。
これらの単位は4種類のヌクレオチド（A、T、G、C）であり、ヌクレオチドの配列は遺伝暗号と呼ばれるアルファベットで情報が保存される。
遺伝子が細胞に読み取られると、DNA配列はRNAと呼ばれる非常に類似した分子に複製される（この過程を転写と呼ぶ）。
転写は、他のDNA配列（プロモーターなど）によって制御される。プロモーターは遺伝子の位置を細胞に示し、遺伝子が複製される頻度を制御する。
遺伝子から複製され作られたRNAは、次にリボソームと呼ばれる構造物に送られ、RNA内のヌクレオチド配列を正しいアミノ酸配列に翻訳され、これらのアミノ酸が結合して完全なタンパク質の鎖が作られる。
その後、新しいタンパク質は機能をもった活性型に折り畳まれる。
RNAの言語からアミノ酸の言語に情報を移動する過程を翻訳と呼ぶ[9]。
If the sequence of the nucleotides in a gene changes, the sequence of the amino acids in the protein it produces may also change—if part of a gene is deleted, the protein produced is shorter and may not work anymore.[6] This is the reason why different alleles of a gene can have different effects on an organism. As an example, hair color depends on how much of a dark substance called melanin is put into the hair as it grows. If a person has a normal set of the genes involved in making melanin, they make all the proteins needed and they grow dark hair. However, if the alleles for a particular protein have different sequences and produce proteins that can't do their jobs, no melanin is produced and the person has white skin and hair (albinism).[10]
Genes are copied
Genes are copied each time a cell divides into two new cells. The process that copies DNA is called DNA replication.[8] It is through a similar process that a child inherits genes from its parents when a copy from the mother is mixed with a copy from the father.
DNA can be copied very easily and accurately because each piece of DNA can direct the assembly of a new copy of its information. This is because DNA is made of two strands that pair together like the two sides of a zipper. The nucleotides are in the center, like the teeth in the zipper, and pair up to hold the two strands together. Importantly, the four different sorts of nucleotides are different shapes, so for the strands to close up properly, an A nucleotide must go opposite a T nucleotide, and a G opposite a C. This exact pairing is called base pairing.[8]
When DNA is copied, the two strands of the old DNA are pulled apart by enzymes; then they pair up with new nucleotides and then close. This produces two new pieces of DNA, each containing one strand from the old DNA and one newly made strand. This process is not predictably perfect as proteins attach to a nucleotide while they are building and cause a change in the sequence of that gene. These changes in the DNA sequence are called mutations.[11] Mutations produce new alleles of genes. Sometimes these changes stop the functioning of that gene or make it serve another advantageous function, such as the melanin genes discussed above. These mutations and their effects on the traits of organisms are one of the causes of evolution.[12]
Genes and evolution
A population of organisms evolves when an inherited trait becomes more common or less common over time.[12] For instance, all the mice living on an island would be a single population of mice: some with white fur, some gray. If over generations, white mice became more frequent and gray mice less frequent, then the color of the fur in this population of mice would be evolving. In terms of genetics, this is called an increase in allele frequency.
Alleles become more or less common either by chance in a process called genetic drift or by natural selection.[13] In natural selection, if an allele makes it more likely for an organism to survive and reproduce, then over time this allele becomes more common. But if an allele is harmful, natural selection makes it less common. In the above example, if the island were getting colder each year and snow became present for much of the time, then the allele for white fur would favor survival since predators would be less likely to see them against the snow, and more likely to see the gray mice. Over time white mice would become more and more frequent, while gray mice less and less.
Mutations create new alleles. These alleles have new DNA sequences and can produce proteins with new properties.[14] So if an island was populated entirely by black mice, mutations could happen creating alleles for white fur. The combination of mutations creating new alleles at random, and natural selection picking out those that are useful, causes an adaptation. This is when organisms change in ways that help them to survive and reproduce. Many such changes, studied in evolutionary developmental biology, affect the way the embryo develops into an adult body.
Inherited diseases
Some diseases are hereditary and run in families; others, such as infectious diseases, are caused by the environment. Other diseases come from a combination of genes and the environment.[15] Genetic disorders are diseases that are caused by a single allele of a gene and are inherited in families. These include Huntington's disease, cystic fibrosis or Duchenne muscular dystrophy. Cystic fibrosis, for example, is caused by mutations in a single gene called CFTR and is inherited as a recessive trait.[16]
Other diseases are influenced by genetics, but the genes a person gets from their parents only change their risk of getting a disease. Most of these diseases are inherited in a complex way, with either multiple genes involved, or coming from both genes and the environment. As an example, the risk of breast cancer is 50 times higher in the families most at risk, compared to the families least at risk. This variation is probably due to a large number of alleles, each changing the risk a little bit.[17] Several of the genes have been identified, such as BRCA1 and BRCA2, but not all of them. However, although some of the risks are genetic, the risk of this cancer is also increased by being overweight, heavy alcohol consumption and not exercising.[18] A woman's risk of breast cancer, therefore, comes from a large number of alleles interacting with her environment, so it is very hard to predict.
Genetic engineering
Since traits come from the genes in a cell, putting a new piece of DNA into a cell can produce a new trait. This is how genetic engineering works. For example, rice can be given genes from a maize and a soil bacteria so the rice produces beta-carotene, which the body converts to vitamin A.[19] This can help children with Vitamin A deficiency. Another gene being put into some crops comes from the bacterium Bacillus thuringiensis; the gene makes a protein that is an insecticide. The insecticide kills insects that eat the plants but is harmless to people.[20] In these plants, the new genes are put into the plant before it is grown, so the genes are in every part of the plant, including its seeds.[21] The plant's offspring inherit the new genes, which has led to concern about the spread of new traits into wild plants.[22]
The kind of technology used in genetic engineering is also being developed to treat people with genetic disorders in an experimental medical technique called gene therapy.[23] However, here the new, properly working gene is put in targeted cells, not altering the chance of future children inheriting the disease causing alleles.
See also
References
- ^ a b University of Utah Genetics Learning Center animated tour of the basics of genetics. Howstuffworks.com. オリジナルの10 February 2008時点におけるアーカイブ。 2008年1月24日閲覧。
- ^ a b Melanocortin 1 Receptor, Accessed 27 November 2010
- ^ Multifactorial Inheritance Health Library, Morgan Stanley Children's Hospital, Accessed 20 May 2008
- ^ Eye color is more complex than two genes, Athro Limited, Accessed 27 November 2010
- ^ “Low income kids' height doesn't measure up by age 1”. University of Michigan Health System. 26 May 2008時点のオリジナルよりアーカイブ。May 20, 2008閲覧。
- ^ a b c The Structures of Life Archived 7 June 2014 at the Wayback Machine. National Institute of General Medical Sciences, Accessed 20 May 2008
- ^ Enzymes HowStuffWorks, Accessed 20 May 2008
- ^ a b c What is DNA? Genetics Home Reference, Accessed 16 May 2008
- ^ DNA-RNA-Protein Nobelprize.org, Accessed 20 May 2008
- ^ What is Albinism? Archived 14 May 2012 at the Wayback Machine. The National Organization for Albinism and Hypopigmentation, Accessed 20 May 2008
- ^ Mutations Archived 15 May 2008 at the Wayback Machine. The University of Utah, Genetic Science Learning Center, Accessed 20 May 2008
- ^ a b Brain, Marshall. “How Evolution Works”. How Stuff Works: Evolution Library. Howstuffworks.com 2008年1月24日閲覧。
- ^ Mechanisms: The Processes of Evolution Archived 27 May 2008 at the Wayback Machine. Understanding Evolution, Accessed 20 May 2008
- ^ Genetic Variation Archived 27 May 2008 at the Wayback Machine. Understanding Evolution, Accessed 20 May 2008
- ^ requently Asked Questions About Genetic Disorders NIH, Accessed 20 May 2008
- ^ Cystic fibrosis Genetics Home Reference, NIH, Accessed 16 May 2008
- ^ Peto J (June 2002). “Breast cancer susceptibility – A new look at an old model”. Cancer Cell 1 (5): 411–2. doi:10.1016/S1535-6108(02)00079-X. ISSN 1535-6108. PMID 12124169.
- ^ What Are the Risk Factors for Breast Cancer? Archived 29 April 2009 at the Wayback Machine. American Cancer Society, Accessed 16 May 2008
- ^ Staff Golden Rice Project Retrieved 5 November 2012
- ^ Tifton, Georgia: A Peanut Pest Showdown USDA, accessed 16 May 2008
- ^ Genetic engineering: Bacterial arsenal to combat chewing insects Archived 15 May 2011 at the Wayback Machine. GMO Safety, Jul 2010
- ^ Genetically engineered organisms public issues education Cornell University, Accessed 16 May 2008
- ^ Staff (November 18, 2005). “Gene Therapy” (FAQ). Human Genome Project Information. Oak Ridge National Laboratory. 2006年5月28日閲覧。
External links
- Introduction to Genetics, University of Utah
- Introduction to Genes and Disease, NCBI open book
- Genetics glossary, A talking glossary of genetic terms.
- Khan Academy on YouTube
- What Color Eyes Would Your Children Have? Genetics of human eye color: An interactive introduction
- Transcribe and translate a gene, University of Utah
- StarGenetics software simulates mating experiments between organisms that are genetically different across a range of traits
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