Lecture_3-4

Lecture_3-4 - Lectures 3/4: Chromosomal Mutations Reading:...

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Unformatted text preview: Lectures 3/4: Chromosomal Mutations Reading: Chapter 16 A) Alterations in whole chromosome sets B) Additions or subtractions of individual chromosomes C) Aberrations within an individual chromosome Euploidy The addition of complete set(s) of chromosomes to a genome Monoploid = 1n Diploid = 2n Triploid = 3n Tetraploid = 4n Etc. 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) 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 AA gives rise to AAAA (A pairs with A and A pairs with A) chromosomes are homeologous endopolyploidy : where certain cells in an otherwise diploid organism become polyploid 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. Pairing of chromosome in a triploid Diploid and tetraploid grapes Pairing of chromosome in a tetraploid Will produce imbalanced gametes viable gametes 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. colchicine Colchicine Blocks Segregation of Chromosomes Effect of Colchicine on Chromosome Segregation Frequency Distribution of Haploid Chromosome number in Plant Species Amphidiploidy in Brassica All same species! 3 rd parental species 2 parental species! 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 Role of polyploids in genome evolution Lecture 2: Chromosomal Mutations A) Alterations in whole chromosome sets B) Additions or subtractions of individual chromosomes C) Aberations within an individual chromosome Aneuploidy The loss or gain of one or more chromosomes from a genome- monosomy the loss of one chromosome: 2n-1- trisomy the addition of one chromosome: 2n+1- nullisomy the loss of one chromosome pair: 2n-2- disomy addition of one chromosome in a haploid: n+1 arise by nondisjunction during mitosis or meiosis note: n+1 gametes have both maternal...
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This note was uploaded on 04/03/2008 for the course BIOL 202 taught by Professor Kieber-hogan during the Spring '08 term at UNC.

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Lecture_3-4 - Lectures 3/4: Chromosomal Mutations Reading:...

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