Chromosomal Mutations Chapter 16

Chromosomal Mutations Chapter 16 - Lectures 3/4:...

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Lectures 3/4: Chromosomal Mutations A) Alterations in whole chromosome sets B) Additions or subtractions of individual chromosomes C) Aberrations within an individual chromosome
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Euploidy The addition of complete set(s) of chromosomes to a genome Monoploid = 1n Diploid = 2n Triploid = 3n Tetraploid = 4n Etc.
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Haploid vs monoploid - The monoploid chromosome set is the basic set of chromosomes multiplied in a ploidy series. - The haploid chromosome set is the set of chromosomes present in a gamete. In diploids, monoploids and haploid are equivalent A tetraploid Arabidopsis plant has 20 chromosomes genome = 4n monoploid chromosomes (n=5) Haploid number of 10 (2n)
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Individual organisms with > two complete sets of chromosomes Polyploids autopolyploidy : Each additional set of chromosomes is identical to the parent species: AA diploid becomes a AAAA tetraploid All the chromosomes are homologous allopolyploidy : Results form the union of two or more distinct chromosome sets (e.g. from the fusion of gametes from closely related species) followed by a subsequent doubling of the chromosome number creates a fertile polyploid. AA plus A’A’ gives rise to AAA’A’ (A pairs with A and A’ pairs with A’) – chromosomes are homeologous endopolyploidy : where certain cells in an otherwise diploid organism become polyploid
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Triploids Typically autopolyploids Can be generated by crossing a tetradploid (4x) X diploid (2x)  triploid (3x) Chromosomes cannot pair evenly at meiosis so triploids are typically sterile.
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Pairing of chromosome in a triploid
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Bananas (Musa x paradisiaca) are triploid (seedless)
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Diploid and tetraploid grapes
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Pairing of chromosome in a tetraploid Will produce imbalanced gametes viable gametes
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How do autopolyploids arise? Can arise spontaneously through nondisjunction of a whole chromosome set. Triploids commonly made by crossing diploids to tetraploids. 2n X 4n = 3n progeny (many seedless fruits) Tetraploids can be induced by treatment with colchicine.
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colchicine Colchicine Blocks Segregation of Chromosomes
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Effect of Colchicine on Chromosome Segregation
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Frequency Distribution of Haploid Chromosome number in Plant Species
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Known Paleopolyploidy in Eukaryotes
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Amphidiploidy in Brassica All same species! 3rd parental species 2 parental species!
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Evolution of modern bread wheat AA BB Wild wheat species X AB Double genome AABB DD X ABD Double genome AABBDD Modern bread wheat an allohexaploid T. searsii? T. monococcum T. turgidum Emmer wheat T. tauschii T. aestivum
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Wheat ( Triticum spp) allohexaploid Rye ( Secale cereale ) diploid Triticale allooctaploid (and others) Triticale (x Triticosecale), an  artificial hybrid of rye and wheat
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Role of polyploids in genome evolution
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Lecture 2: Chromosomal Mutations A) Alterations in whole chromosome sets B) Additions or subtractions of individual chromosomes C) Aberations within an individual chromosome
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Aneuploidy The loss or gain of one or more chromosomes from a genome - monosomy the loss of one chromosome: 2n-1
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Chromosomal Mutations Chapter 16 - Lectures 3/4:...

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