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2010-04-15 11:19:51

Biol117 Human Genetic CH9
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  1. Types of point mutations:
    • 1. base-pair substitutions
    • 2. indels
    • 3. frameshifts
    • 4. triplet repeats
  2. Gnome Mutation
    • Cause by missegregation of a chromosome pair during meiosis. ex trisomy 21.
    • It produces chromosomal aneuploidy and are the most common mutation in human.
  3. Chromosome Mutation
    • occuring 1/1700 cell division. Rarely pass to next generation due to its incompatible with survival or normal reproduction.
    • his is also frequently seen in cancer cell.
  4. Gene Mutation
    • includes base pair substitution, insertions and deletions.
    • Orginate by either: errors introduced during the DNA replication; or mutations from a failure to repair DNA after damage.
    • Gene Muattion can be either spontaneous or introduced by Mutagens
  5. he Origin of Mutations
    • - Gnome
    • - Chromosome
    • - Gene
    • - DNA Replication errors
    • - Repair of DNA damage
  6. Nucleotide Substitution:
    • - Missense
    • - Chain Termination
    • - RNA Processing
    • - Hotspot of mutation
  7. Misseense Mutation
    • A single nucleotide substitution( or point mutation) which alter the triplet code = missense.
    • Most of detected mutations are missense.
    • Other point mutation occurs either within or outside the code sequence of a gene can also have extensive effects.
    • ie: mutations in the 5' promoter region or the 3' untranslated region of the B globin gene lead to the sharp decrease of B-globin mRNA produced.
  8. Chain Termination Mutations
    • =nonsense mutation
    • cause: 1.mRNA carrying a premature and is unstable(nonsense-mediated mRNA decay), no translatio.
    • 2. even if the RNA is stable enough to be translated, the truncated protein is usually unstable and degraded within the cell.
    • 3. point mutation may also destory a termination codon and let translation to contiune until reach the next stop codon. such a mutation may disrupt any regulatory function on 3' end untranslated region downstream from normal stop codon.
  9. RNA Processing Mutations
  10. Transition s Transversion
    • Transition: Purine-Purine/Pyrimidine-Pyrimidine (A-G, G-A or C-T, T-C)
    • Transversion: Purine-Pyrimidine
    • If random, Transversion vs Transition = 2:1
  11. Large Deletions and Insertions
    Alterations large enough to be dectected by Southern Blotting.
  12. Single-nucleotide polymorphism (SNPs)
    • is a DNA sequence variation occurring when a single nucleotide — A, T, C, or G — in the genome
    • (or other shared sequence) differs between members of a species (or
    • between paired chromosomes in an individual). For example, two
    • sequenced DNA fragments from different individuals, AAGCCTA to AAGCTTA, contain a difference in a single nucleotide. In this case we say that there are two alleles : C and T. Almost all common SNPs have only two alleles.
    • Within a population, SNPs can be assigned a minor allele frequency — the lowest allele frequency at a locus
    • that is observed in a particular population. This is simply the lesser
    • of the two allele frequencies for single-nucleotide polymorphisms.
    • There are variations between human populations, so a SNP allele that is
    • common in one geographical or ethnic group may be much rarer in another. (wiki)
  13. Insertion-Deletion Polymorphisms
    • this class is result of indel between 2 to 100 nucleotides, 100 to 1000 in genome.
    • 1/2 of all indels are simple b/c they have only 2 alleles.
    • The other half are mutiallelic due to variable numbers of a segment. This includes Microsatellite and Minisatellite.
  14. Microsatellites
    • =Short tandem repeat polymorphism(STRPs), are repeating sequences of 1-6 base pairs of DNA. Repeat one to few dozen times.
    • Microsatellites can be amplified for identification by the polymerase chain reaction (PCR) process, using the unique sequences of flanking regions as primers.
  15. Minisatellite
    • =variable number tandem repeats (VNTRs)
    • This class has many alleles due to variation in the number of copies of the minisatellite that are repaeted in tandem.
    • Method first used in DNA fingerprinting. Now use typing of microsatellites by PCR instead of detection by southern blotting.
  16. (一)限制性片段长度多态性(Restriction Fragment Length Polymorphism,RFLP)
    • 限制性片段长度多态性是出现最早和应用最广泛的DNA标记技术之一。1974年Grodzicker等创立了该技术,它是一种以DNA—DNA杂交为基础
    • 的第一代遗传标记。RFLP标记非常稳定,它是一种共显性标记,在分离群体中可区分纯合体与杂合体,提供标记位点完整的遗传信息。多种农作物的RFLP分
    • 子遗传图谱已经建成。但其分析所需DNA量较大,步骤较多,周期长,制备探针及检测中要用到放射性同位素,尽管可用非放射性同位素标记方法代替,但成本
    • 高、成功率低,且实验检测步骤较多,依然影响其使用、推广。自RFLP问世以来,已经在基因定位及分型、遗传连锁图谱的构建、疾病的基因诊断等研究中仍得
    • 到了广泛的应用。  RFLP基本原理:利用特定的限制性内切酶识别并切割不同生物个体的基因组DNA,得到大小不等的DNA片段,所产
    • 生的DNA数目和各个片段的长度反映了DNA分子上不同酶切位点的分布情况。通过凝胶电泳分析这些片段,就形成不同带,然后与克隆DNA探针进行
    • Southern杂交和放射显影,即获得反映个体特异性的RFLP图谱。它所代表的是基因组DNA在限制性内切酶消化后产生片段在长度上差异。由于不同个
    • 体的等位基因之间碱基的替换、重排、缺失等变化导致限制内切酶识别和酶切发生改变从而造成基因型间限制性片段长度的差异。
  17. (二)小卫星DNA(Minisatellite DNA)
    • 小卫星DNA(Minisatellite DNA)又称数目可变串联重复序列(Variable Number of Tandem
    • Repeat,VNTR)是一种重复DNA小序列,为10到几百核苷酸,拷贝数10—10000不等。多态性由于重复单位之间的不平衡交换,从而产生不同
    • 等位基因,可通过杂交检测出。其缺点是多态性分布集中,数量有限,而且在基因组上分布不均匀,合成探针困难,实验操作繁琐、检测时间长、成本高,因此应用
    • 并不广泛。  VNTR基本原理与RFLP大致相同,只是对限制性内切酶和DNA探针有特殊要求:(1)限制性内切酶的酶切位点必须不在
    • 重复序列中,以保证小卫星或微卫星序列的完整性。(2)内切酶在基因组的其他部位有较多酶切位点,则可使卫星序列所在片段含有较少无关序列,通过电泳可充
    • 分显示不同长度重复序列片段的多态性。(3)分子杂交所用DNA探针核昔酸序列必须是小卫星序列或微卫星序列,通过分子杂交和放射自显影后,就可一次性检
    • 测到众多小卫星或微卫星位点,得到个体特异性的DNA指纹图谱。
  18. Copy Number Polymorphisms
    • = CNPs.
    • CNPs may have only two alleles or multiple alleles due to te copies (0,1,2,3...) of a segment of DNA in tandem.
    • This have only be recently i.d. b/c deleted or repeated regions are too small to detect by cytogenetic examination but too large for DNA sequencing.
    • Its discover by Array Comparative genome hybridization.
  19. phenylketonuria (PKU)
    • A hereditary disorder that results in reduced production of the liver enzyme
    • phenylalanine hydroxylase. This substance is involved in the breakdown
    • of phenylalanine in food to tyrosine. Without a modified diet, affected
    • infants will develop severe, irreversible brain damage.
  20. Polymorphism
    Occurrence in a population of two or more alleles, usually at freq of 1% or higher.
  21. Splice site mutation
    Mutations that either destory the normal splicing site or create a new splice site at an inappropriate location.
  22. Mini satellite
    DNA maker create by the tandem repeats of a DNA sequence of 6 to 100 nucleotides