清华大学：《分子生物学》课程PPT教学课件（基因ene）第四章 簇和重复（Clusters and repeats）

Chapter 4 Clusters and repeats 清苇大当

Chapter 4 Clusters and repeats

Gene clusters are formed by duplication and divergence Sequence divergence is the basis for the evolutionary clock Pseudogenes are dead ends of evolution Unequal crossing-over rearranges gene clusters Genes for rRNA form tandem repeats The repeated genes for rRNA maintain constant sequence) Crossover fixation could maintain identical repeats Satellite DNAs often lie in heterochromatin Arthropod satellites have very short identical repeats Mammalian satellites consist of hierarchical repeats Minisatellites are useful for genetic mapping 清苇大当

Gene clusters are formed by duplication and divergence Sequence divergence is the basis for the evolutionary clock Pseudogenes are dead ends of evolution Unequal crossing-over rearranges gene clusters Genes for rRNA form tandem repeats ( The repeated genes for rRNA maintain constant sequence) Crossover fixation could maintain identical repeats Satellite DNAs often lie in heterochromatin Arthropod satellites have very short identical repeats Mammalian satellites consist of hierarchical repeats Minisatellites are useful for genetic mapping

4.1 Introduction Gene cluster is a group of adjacent genes that are identical or related. Gene family consists of a set of genes whose exons are related;the members were derived by duplication and variation from some ancestral gene. Satellite DNA consists of many tandem repeats(identical or related) of a short basic repeating unit. Unequal crossing-over describes a recombination event in which the two recombining sites lie at nonidentical locations in the two parental DNA molecules. 情菜大当

Gene cluster is a group of adjacent genes that are identical or related. Gene family consists of a set of genes whose exons are related; the members were derived by duplication and variation from some ancestral gene. Satellite DNA consists of many tandem repeats (identical or related) of a short basic repeating unit. Unequal crossing-over describes a recombination event in which the two recombining sites lie at nonidentical locations in the two parental DNA molecules. 4.1 Introduction

4.1 Bivalent contains 4 A chromatids,2 fromeach A parent Introduction aaQ b ↓ Chiasma is caused by A A aA Figure 1.23 crossing-over between 2 of the chromatids Chiasma formation is Two chromosomes remain responsible parental(48 and a月 A Recombinant chromosomes B A for generating contain material fromeach parent,and have new genetic recombinants. combinations (Ab and aB). a 清菜大当

Figure 1.23 Chiasma formation is responsible for generating recombinants. 4.1 Introduction

Parental DNA molecules 4.1 58533583553555555 99889白888698698B8898i Introduction Figure 1.24 Recombination intemmediate Recombination 38-555555558555555858 9988998863B898营88959 involves pairing 8355558555355885555o808 between 9G8889888a08a988888086 complementary strands of the Recombinants two parental 35558558588565688 88的9888G白8g988888的白 duplex DNAs. 88558358858855555 9G8Bg9B88G98位Q88意a3a 情華大兰

Figure 1.24 Recombination involves pairing between complementary strands of the two parental duplex DNAs. 4.1 Introduction

4.2 Gene clusters are formed by duplication and divergence Pseudogenes are inactive but stable components of the genome derived by mutation of an ancestral active gene. 假基因：类似于基因但不表达的DNA序列。 不表现任何功能，是基因的退化形式。假基因在基因组中形成 稳定的和无活性的拷贝，由活化的原始基因突变而来，这是因 为存在着在某个阶段伤及基因表达的一种或多种缺陷（入启动 子错误、有缺陷的剪接信号、框架中有终止信号等)之故。 旦不能产生正常的基因产物，就失去了对发生进一步突变的选 择性屏障作用，因此典型的假基因都有很多缺陷。某些假基因 有3-多聚A尾巴及准确地切掉了内含子，因而与mRNA类似， 被认为是源自插入基因组的逆转录体（可能由某些病毒携带） 清苇大当

Pseudogenes are inactive but stable components of the genome derived by mutation of an ancestral active gene. 假基因：类似于基因但不表达的DNA序列。 不表现任何功能，是基因的退化形式。假基因在基因组中形成 稳定的和无活性的拷贝，由活化的原始基因突变而来，这是因 为存在着在某个阶段伤及基因表达的一种或多种缺陷（入启动 子错误、有缺陷的剪接信号、框架中有终止信号等）之故。一 旦不能产生正常的基因产物，就失去了对发生进一步突变的选 择性屏障作用，因此典型的假基因都有很多缺陷。某些假基因 有3‘-多聚A尾巴及准确地切掉了内含子，因而与mRNA类似， 被认为是源自插入基因组的逆转录体（可能由某些病毒携带）。 4.2 Gene clusters are formed by duplication and divergence

4.2 Gene clusters are formed by duplication and divergence Exon 1 Intron 1 Exon 2 Intron 2 Exon 3 日ase pairs142-145116-130 222 573-904 216-255 5'nontranslated acids Coding 105-end +c0ing1-30 +3'nontranslated Figure 2.13 All functional globin genes have an interrupted structure with three exons.The lengths indicated in the figure apply to the mammalian b- globin genes. 清華大当

Figure 2.13 All functional globin genes have an interrupted structure with three exons. The lengths indicated in the figure apply to the mammalian b￾globin genes. 4.2 Gene clusters are formed by duplication and divergence

4.2 Gene clusters Ψ0 Ψ002016 are formed by g 鸣 o cluster duplication and Ψβ divergence B cluster Figure 4.1 Each of the a-like and b-like 10 20 30 40 50 kb globin gene families is organized into a Human hemoglobins change during development single cluster that includes functional Stage of Development Hemoglobins genes and Embryonic (<8 weeks) 522 52Y2022 Fetal (3-9 months) 0i22 pseudogenes Adult(from birth) 2820z2 清菜大兰

Figure 4.1 Each of the a-like and b-like globin gene families is organized into a single cluster that includes functional genes and pseudogenes. 4.2 Gene clusters are formed by duplication and divergence

4.2 Gene clusters are formed by duplication and divergence Early embryonic Adult Mouse B29 Late embryonic Rabbit Chicken 60 50 40 30 20 10k幼 Figure 4.2 Clusters of b-globin genes and pseudogenes are found in vertebrates.Seven mouse genes include 2 early embryonic,1 late embryonic,2 adult genes,and 2 pseudogenes.Rabbit and chick each have four genes. 清菜大当

Figure 4.2 Clusters of b-globin genes and pseudogenes are found in vertebrates. Seven mouse genes include 2 early embryonic, 1 late embryonic, 2 adult genes, and 2 pseudogenes. Rabbit and chick each have four genes. 4.2 Gene clusters are formed by duplication and divergence

4.2 Gene Separate clusters mammals&birds】 B1 B2 clusters are UNI I formed by Expansion of cluster 02 duplication and o■ divergence Separation of genes Linked o B Figure 4.3 All globin genes (Xenopus) Duplication divergence genes have evolved by 8n開 a series of duplications, Ancestral globin (myoglobin transpositions,and Exon fusio or Intron insertion mutations from a Leghemoglobin (plants) single ancestral gene. 700600500400300200100 Million years 清苇大当

Figure 4.3 All globin genes have evolved by a series of duplications, transpositions, and mutations from a single ancestral gene. 4.2 Gene clusters are formed by duplication and divergence