Chapter 8: Chromosome Mutations *Chromosome mutations/aberrations Variation in chromosome number: *aneuploidy *euploidy *polyploidy Nondisjunction Homologous chromosomes: during anaphase I Sister chromatids: during anaphase II Monosomy *Condition in which one member of a chromosome pair is missing (2n-1) In Drosophila: Haplo-IV are monosomic for chromosome 4 *develop more slowly, reduced size, impaired viability In Plants: Maize, tobacco, evening primrose, Jimson weed *Segmental deletions *Cri-du-chat (46,5p-) Trisomy *Condition in which one chromosome is present in three copies (2n+1) In Plants: Jimson weed, rice In Drosophila and humans: Has severe effects, usually lethal Exceptions: Patau syndrome, 47,13+ Edwards syndrome, 47,18+ Down syndrome, 47,21+ Polyploidy 1) Addition of one or more sets of chromosomes (replication) 2) Combination of chromosome sets from different species Polyploidy Autopolyploidy Arise in several ways: *failure of all chromosomes to segregate during meiosis *two sperm may fertilize an ovum *experimentation The benefits of autopolyploid breeding: increased size of plant organs- roots, leaves, flowers fruits, seeds Polyploidy Allopolyploidy Variations in Chromosome Structure Deletions Variations in Chromosome Structure Duplications Crossover: A B C D D A B C D D D A B C D A B C D A B C D A B C D A B C D A B C A A B B C C D D A A B B C C Due to unequal crossing over: Evolution of hemoglobin genes Variations in Chromosome Structure Inversions *Paracentric *Pericentric Variations in Chromosome Structure Translocation Variations in Chromosome Structure Translocation – unbalanced gametes are produced
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