LS6genome - Lecture 6: Genome structure Gene and genome...

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1 Lecture 6: Genome structure Gene and genome structure Simple-sequence repeats Chromosome structure Chromatin structure Nucleosome Histones Nuclear DNA Mitochondria DNA Chloroplasts DNA DNA in prokaryoic and eukaryotic cells
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2 Organiation and content of the human genome
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3 Yeast: 12 Mb genome encodes ~5000 genes: gene/2.4kb Human: 3,300 Mb genome encodes ~25,000 genes: gene/132 kb For example, there are 5 structure genes in this 80 kb human genome region, in contrast to 48 ORF in a 80 kb region of the yeast genome. Different organisms have different gene density
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4 Comparison of the Chromosomal Gene Density in the Genomes of Different Organisms Conclusions: •Bacterial genomes have densely packed protein-coding genes, with minimal non-coding DNA sequences •Gene density decreases with increased biological complexity in eukaryotes •Protein-coding genes of higher eukaryotes have more and larger introns than lower eukaryotes •Amount of intron sequences (non-coding transcribed DNA) increases with biological complexity in higher eukaryotes Genes Repetitive DNA Two types of genomic DNA
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5 2. Simple-sequence repeats Satellite DNA may result from errors in DNA replication, and they are often associated with human genetic disease. Some satellite DNA are highly diverged among individuals so they can be used as markers for genetic testing (such as parental identification). The function of most satellite DNA remains unknown The simple sequence repeat DNAs are also called satellite DNAs, because they often migrate as “satellite bands” in density gradient centrifugation. The simple sequence repeat are 14-500bp sequences that form tandem repeat of up to 10-100kb, which are particularly abundant in centromeres and telomeres of chromosomes. Two smaller repeats: mini-satellite DNA ( 14- 100bp, repeats up to 1-5kb) and micro-satellite DNA ( 1-40bp, repeats up to 150 bp) are found in many places of the genome. The length of simple- sequence repeats are often different among individuals. Such length
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LS6genome - Lecture 6: Genome structure Gene and genome...

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