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17 Cards in this Set
- Front
- Back
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How are genes from the human genome found? |
- Identifying DNA corresponding to known human proteins and/or mRNAs, or to sequenced but uncharacterised mRNAs ESTs - identifying DNA corresponding to genes from other species - using computer analysis to detect previously unknown genes (ab initio prediction) |
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What is ab initio prediction? |
- using computer to detect previously unknown genes - comparatively easy in prokaryotes - just got to look for long ORFs - but long ORFs in eukaryotes are interrupted by introns => gene prediction is way more difficult |
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What are the questions that should be asked about the investigated DNA before doing ab initio prediciton? |
- is there evidence that DNA is transcribed - does DNA show evolutionary conservation - does DNA have predicted exons - does combining these exons generate potential ORF |
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How do you distinguish conserved non-coding DNA from conserved protein-coding DNA. |
- Protein-coding DNA - base substitutions (SNPs) separated by three nucleotides - e.g. SOX9 gene from human and 3 fish - substitution on every 3rd nucleotide - each of the DNA seq - encode same AA seq |
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How many genes are there in the human genome? |
20 000 - 22 000? BUT many more proteins! |
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Why are there more proteins than genes discovered? |
- alternative splicing - 20-90% of genes show it - each alternatively spliced gene produces an average of 4 different mRNAs => human genome may encode over 60 000 proteins |
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Average human gene - numbers |
- exons - 11 - median exon size - 140bp - median intron size - 1700 bp - average gene size - 54 000 |
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What is the biggest known gene? |
Dystrophin (DMD): 2400 kb - including a 250 000 intron
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What is the biggest protein? |
- Titin - 36 000 AAs encoded by a gene with 364 exons |
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Gene density and gene number varies between chromosomes. Which chromosome has highest gene density and which lowest? |
- Highest - 19 - 22.5 genes per Mb - Lowest - y 0.76 genes per Mb |
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There could be up to 20 000 genes that encode functional RNA that is not mRNA. What are they? |
- tRNA and rRNA - snRNA and snoRNA - involved in splicing - miRNA - regulate stability and translation - Long non-coding RNAs with regulatory enzymic or structural roles |
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Most genes occur in a single copy but genes have more. Why? |
- if the genes encode proteins that are very abundant - e.g. Histone - humans have approx 61 copies of each histone gene |
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Most human genes belong to a gene family. What is that? |
- family of related genes all derived from a common ancestor - members of gene families may be clustered or dispersed |
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What are homologues? |
- Genes that share a common ancestor |
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What are orthologues? |
- two homologous genes arising as a result of a species divergence |
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What are paralogues? |
- two homologous genes arising as a result of a gene duplication |
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How can functional DNA be identified? |
- Encodes a protein or known functional RNA - more evolutionarily conserved - genetic anal. - knock in knock out - biochem function - transcribed, associated with histone, in open chromatin, bound by a TF |
