清华大学：《分子生物学》（英文版）Chapter 4 Clusters and repeats

Chapter 4 Clusters and repeats 莘大

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 消当

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 消当

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 chromatids. 2 from each parent Introduction AAa chiasma is caused by Figure 1.23 crossing-over between 2 of the chromatids AAa Bb Chiasma formation is Two chromosomes remain responsible parental( AB and a总 Recombinant chromosomes A or generating contain material from each parent, and have new genetic a combinations (Ab and aB) B recombinants a 消当

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

Parental dNa molecules Introduction 白意意意 Figure 1.24 Recombination intem ediate Recombination involves pairing between complementary strands of the Recom binants two parental bb6Q点b点bbbb6 9露日露白日 duplex dnas 583883 意意白 8意念危意意 消当

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 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) 消当

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 Base pairs142-145116-130222 573-904 216-255 5 nontranslated Am ino acids Coding 105-end +coding 1-30 31-104 +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 消当

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 5u2c16 are formed by ■■■ or cluster duplication and divergence 阝 cluster Figure 4.1 Each of the a-like and b-like 20 globin gene far milles is organized into a Human hemoglobins change during development single cluster that includes functional Stage of Development Hemoglobins genes and Embryonic (<8 weeks) 52E2 5222 a2E2 Fetal (3-9 months) 2Y2 pseudogenes Adult (from birth) 消当

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 u Bho Fnh2 h3 1 ut Early embryonic Adu Mouse■ Late embl P4阝3哪1 Rabbit■ Chicken p58 60 50 40 30 20 10 kb Figure 4.2 Clusters of b-globin genes and pseudogenes are found in vertebrates. Seven mouse genes include 2 early embryonic, I late embryonic, 2 adult genes, and 2 pseudogenes. Rabbit and chick each have four genes 消当

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) 1 clusters are formed by y Expansion of cluster duplication and div Vergence Separation of genes Linked o&阝 Figure 4.3 All globin genes (Xenopus) Duplication divergance renes have evolved by Single globin gene hagfish a series of duplications Ancestral globin (myoglobin transpositions, and Exon fusil■ar■| tron insertion mutations from a ■■ Leghemoglobin (plants) single ancestral gene 700600500400300200100 消当

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