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1. Unequal Crossing-Over a. process: If homologs line up askew:
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: If homologs line up askew: A B a b
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1. Unequal Crossing-Over a. process: If homologs line up askew
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: If homologs line up askew And a cross-over occurs A a b B
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1. Unequal Crossing-Over a. process: If homologs line up askew
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: If homologs line up askew And a cross-over occurs Unequal pieces of DNA will be exchanged… the A locus has been duplicated on the lower chromosome and deleted from the upper chromosome A a b B
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1. Unequal Crossing-Over a. process: b. effects: - can be bad:
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: b. effects: - can be bad: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration
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1. Unequal Crossing-Over a. process: b. effects: - can be bad:
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: b. effects: - can be bad: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration - can be good: more of a single protein could be advantageous (r-RNA genes, melanin genes, etc.)
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1. Unequal Crossing-Over a. process: b. effects: - can be bad:
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement 1. Unequal Crossing-Over a. process: b. effects: - can be bad: deletions are usually bad – reveal deleterious recessives additions can be bad – change protein concentration - can be good: more of a single protein could be advantageous (r-RNA genes, melanin genes, etc.) source of evolutionary novelty (Ohno hypothesis ) where do new genes (new genetic information) come from?
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Gene A Duplicated A generations Mutation – may even render the protein non-functional But this organism is not selected against, relative to others in the population that lack the duplication, because it still has the original, functional, gene.
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Gene A Duplicated A generations Mutation – may even render the protein non-functional Mutation – other mutations may render the protein functional in a new way So, now we have a genome that can do all the ‘old stuff’ (with the original gene), but it can now do something NEW. Selection may favor these organisms.
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If so, then we’d expect many different neighboring genes to have similar sequences. And non-functional pseudogenes (duplicates that had been turned off by mutation). These occur – Gene Families
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And, if we can measure the rate of mutation in these genes, then we can determine how much time must have elapsed since the duplication event… Gene family trees…
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Mechanism #1: Exon Shuffling
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement E. Change in Gene Structure Mechanism #1: Exon Shuffling Crossing over WITHIN a gene, in introns, can recombine exons within a gene, producing new alleles. Allele “a” EXON 1a EXON 2a EXON 3a Allele “A” EXON 1A EXON 2A EXON 3A
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Mechanism #1: Exon Shuffling
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement E. Change in Gene Structure Mechanism #1: Exon Shuffling Crossing over WITHIN a gene, in introns, can recombine exons within a gene, producing new alleles. EXON 1a EXON 2a EXON 3a Allele “a” EXON 1A EXON 2A EXON 3A Allele “A” Allele “α” Allele “ά”
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1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement E. Change in Gene Structure 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations a. addition/deletion: “frameshift” mutations …T C C G T A C G T …. Normal …A G G C A U G C A … ARG HIS ALA Mutant: A inserted …T C C A G T A C G T …. …A G G U C A U G C A … SER CYS DNA m-RNA Throws off every 3-base codon from mutation point onward
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1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement E. Change in Gene Structure 1. Mechanism #1: Exon Shuffling 2. Mechanism #2: Point Mutations a. addition/deletion: “frameshift” mutations b. substitution … T C C G T A C G T …. Normal …A G G C A U G C A … DNA m-RNA ARG HIS ALA Mutant: A for G …T C C A T A C G T …. …A G G U A U G C A … TYR At most, only changes one AA (and may not change it…)
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Sources of Variation Causes of Evolutionary Change
VI. Mutation Overview Changes in Ploidy Changes in ‘Aneuploidy’ (changes in chromosome number) D. Change in Gene Number/Arrangement E. Change in Gene Structure F. Summary Sources of Variation Causes of Evolutionary Change MUTATION: Natural Selection -New Genes: point mutation Mutation (polyploidy can make new exon shuffling species) RECOMBINATION: - New Genes: crossing over -New Genotypes: independent assortment VARIATION
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