Chapter 8 course outline B2009

Chapter 8 course outline B2009 - BB 3140 Course Outline...

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BB 3140 Course Outline Chapter 8 Origin of Genetic Variation I. Genes and Genomes A. Steps in eukaryotic gene expression (Fig. 8.1) 1. Transcription produces pre-mRNA 2. Splicing removes introns (non-coding sequences) and produces mRNA 3. Ribosomes translate mRNA sequences into proteins B. The genetic code (Fig. 8.2) 1. triplet code 2. no punctuation 3. 61 amino acid codons, 3 stop codons 4. only 20 amino acids, so code is degenerate 5. code is universal 6. amino acid sequence determines protein function C. Organization of eukaryotic genomes 1. Much of the human genome consists of simple repeated sequences of a few base pairs a. 45% of total genome size b. 4.3 million repeated elements c. repeats include several types of elements i. microsatellites ii. tandem repeats (clusters) iii. SINES (100-400 bp) iv. LINES (5000 bp) v. transposons 2. 80% of total human genome is transcribed a. overall only 5% of human genome encodes proteins b. the rest is RNA molecules, introns 3. 40% of all human genes are members of multi-gene families a. example: human globin genes (Fig. 8.3) b. some gene families are huge i. olfactory receptors in mouse: 1000 genes c. many genes in gene families may be pseudogenes II. Gene mutations A. Mutation is an inheritable alteration in a DNA sequence a. can refer to the altered DNA molecule or the process of alteration b. a mutation is not a cell or organism; such an entity is referred to as a mutant. B. Different forms of a gene are referred to as alleles 1. alleles can be recognized by differences in phenotypes, but the real differences between alleles are in DNA sequence
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2. because most genes are long DNA sequences (thousands of bp), many alleles are possible (4 n where n = number of bp in gene sequence 3. mutations may or may not affect phenotype a. example: synonymous base substitutions (silent mutations) b. example: change from one amino acid codon to a codon encoding a similar amino acid C. For evolution mutations occurring in the germ line are most important 1. only mutations in the germ line cells (gametes) are inherited 2. mutations in somatic cells may produce differences in
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Chapter 8 course outline B2009 - BB 3140 Course Outline...

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