ဗီဇဗေဒ မိတ်ဆက်: တည်းဖြတ်မှု မူကွဲများ

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စာကြောင်း ၆ -
 
သတ်မှတ်ထားသည့် ဗီဇတစ်ခုအတွင်း ပါဝင်သည့် အချက်အလက်များသည့် သက်ရှိတစ်ခုနှင့် တစ်ခုအကြား အမြဲတစေ တထပ်တည်း မဟုတ်ပေ။ ဥပမာ လူနှစ်ဦးတွင် တူညီသည့် ဗီဇများ ပါရှိသည် ဆိုဦးတော့ ယင်းဗီဇများ၏ လုပ်ဆောင်မှု တထပ်တည်း ဖြစ်ချင်မှ ဖြစ်မည်။ ဗီဇတစ်ခု၏ သူမတူသည့် ယူနစ်တစ်ခုကို အယ်လီ (allele) ဟု ခေါ်သည်။ ဥပမာအားဖြင့် အမွေးအမှင်များ၏ အရောင်ကို သတ်မှတ်ပေးသည့် ဗီဇ၏ အယ်လီတစ်ခုသည် ခန္ဓာကိုယ်အား pigment ခေါ် ဆိုးဆေးများ အမြောက်အမြား စစ်ထုတ်ရန် ညွှန်ကြားပေး၍ အနက်ရောင် ဖြစ်စေနိုင်သည်။ တခြားတဖက်တွင် ထိုဗီဇမှပဲ အခြားအယ်လီမှ တိကျသည့် ညွှန်ကြားချက် မပေးနိုင်၍ အဖြူရောင် ဖြစ်စေနိုင်သည်။ [[မြူတေးရှင်း]] (Mutation) ဆိုသည်မှာ ဗီဇသင်္ကေတများ ကျပန်း ပြောင်းလဲခြင်းဖြစ်ပြီး အယ်လီ အသစ်များကို ဖန်တီးနိုင်သည်။ မြူတေးရှင်းမှလည်း လက္ခဏာအသစ်များ ပေါ်ထွန်းလာနိုင်သည်။ ဤသို့ လက္ခဏာအသစ် ပေါ်ထွန်းခြင်းသည်လည်း သက်ရှိများ [[ဆင့်ကဲပြောင်းလဲခြင်း]] (evolution) ဖြစ်စဉ်တွင် အရေးပါသည့် အချက်ဖြစ်သည်။
 
== ဗီဇများ အလုပ်လုပ်ပုံ ==
===ပရိုတိန်းဖွဲ့စည်းခြင်း===
ဗီဇများ၏ လုပ်ငန်းတာဝန်တစ်ရပ်မှာ ဆဲလ်အတွင်း ပရိုတိန်းဖွဲ့စည်းရာ၌ လိုအပ်သည့် အချက်အလက်များ ပံ့ပိုးပေးရန်ဖြစ်သည်။<ref name=Utah>{{Cite book| title =University of Utah Genetics Learning Center animated tour of the basics of genetics| publisher =Howstuffworks.com | url =http://learn.genetics.utah.edu/units/basics/tour|format = web resource|accessdate=2008-01-24 }}</ref> ဆဲလ်များသည် သက်ရှိများ၏ အသေးငယ်ဆုံး အခြေခံ အစိတ်အပိုင်းဖြစ်သည်။ လူသားတစ်ဦးတွင် ဆဲလ်အရေအတွက်ပေါင်း ၁၀၀ ထြီလျံခန့် ရှိသည်။ အသေးငယ်ဆုံး သက်ရှိဖြစ်သည့် [[ဗက်တီးရီးယား]]များတွင် ဆဲလ် တစ်ခုသာရှိသည်။ ဆဲလ်များသည် အသေးစား စက်ရုံတစ်ရုံနှင့် ဆင်တူပြီး ဆဲလ်များ ကွဲထွက်ရာတွင် ထပ်တူညီမျှသည့် ဆဲလ်တစ်ခုကို ထုတ်ပေးနိုင်စွမ်းရှိသည်။
<!--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 damage.<ref name=NIGMS>[http://publications.nigms.nih.gov/structlife/chapter1.html The Structures of Life] National Institute of General Medical Sciences, Accessed 20th May 2008</ref> 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.
 
[[Image:Genetic code.svg|thumb|image|right|280px|Genes are expressed by being [[transcription (genetics)|transcribed]] into RNA, and this RNA then [[protein biosynthesis|translated]] into protein.]]
 
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 will do.<ref name=NIGMS/> 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 [[enzyme]]s, which are like tiny machines that alter other molecules.<ref>[http://www.howstuffworks.com/cell2.htm Enzymes] HowStuffWorks, Accessed 20th May 2008</ref>
 
The information in DNA is held in the sequence of the repeating units along the DNA chain.<ref name=nih>[http://ghr.nlm.nih.gov/handbook/basics/dna What is DNA?] Genetics Home Reference, Accessed 16 May 2008</ref> These units are four types of [[nucleotide]]s (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 (genetics)|transcription]]). Transcription is controlled by other DNA sequences (such as [[Promoter (biology)|promoter]]s), 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 DNA into the language of amino acids is called [[protein biosynthesis|translation]].<ref name=nobel>[http://nobelprize.org/educational_games/medicine/dna/index.html DNA-RNA-Protein] Nobelprize.org, Accessed 20th May 2008</ref>
 
[[Image:DNA replication split.svg|thumb|left|[[DNA replication]]. DNA is unwound and [[nucleotide]]s are matched to make two new strands.]]
 
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 will be shorter and may not work any more.<ref name=NIGMS/> This is the reason why different alleles of a gene can have different effects in 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 will be produced and the hair will be white. This condition is called [[albinism]] and the person with this condition is called an albino.<ref>[http://www.albinism.org/publications/what_is_albinism.html What is Albinism?] The National Organization for Albinism and Hypopigmentation, Accessed 20 May 2008</ref>
 
===Genes are copied===
 
Genes are copied each time a cell divides into two new cells. The process that copies DNA is called [[DNA replication]].<ref name=nih/> 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 creation 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 in order 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]].<ref name=nih/>
 
When DNA is copied, the two strands of the old DNA are pulled apart by enzymes which move along each of the two single strands pairing up new nucleotide units and then zipping the strands closed. This produces two new pieces of DNA, each containing one strand from the old DNA and one newly made strand. This process isn't perfect and sometimes the proteins will make mistakes and put the wrong nucleotide into the strand they are building. This causes a change in the sequence of that gene. These changes in DNA sequence are called [[mutation]]s.<ref>[http://learn.genetics.utah.edu/units/disorders/mutations/ Mutations] The University of Utah, Genetic Science Learning Center, Accessed 20th May 2008</ref> Mutations produce new alleles of genes. Sometimes these changes stop the gene from working properly, like the melanin genes discussed above. In other cases these mutations can change what the gene does or even let it do its job a little better than before. These mutations and their effects on the traits of organisms are one of the causes of [[evolution]].<ref name=Marshall/>
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