Mutation Overview: Changes in Ploidy, Aneuploidy, and Gene Structure

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

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 B a b

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 B A a b

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

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.)

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 - 1970) • where do new genes (new genetic information) come from?

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.

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.

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

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…

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

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 EXON 1A EXON 2a EXON 3a Allele “α” EXON 2A EXON 3A EXON 1a Allele “ά”

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 Normal Mutant: A inserted DNA …T C C G T A C G T …. …T C C A G T A C G T …. …A G G C A U G C A … …A G G U C A U G C A … m-RNA ARG SER CYS ARG HIS ALA Throws off every 3-base codon from mutation point onward

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 Normal Mutant: A for G DNA … T C C G T A C G T …. …T C C A T A C G T …. …A G G C A U G C A … …A G G U A U G C A … m-RNA ARG TYR ALA ARG HIS ALA At most, only changes one AA (and may not change it…)

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 VariationCauses 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: crossing over independent assortment VARIATION

Mutation Overview: Changes in Ploidy, Aneuploidy, and Gene Structure