Chapter 8: Chromosome Mutations *Chromosome mutations/aberrations Variation in chromosome number: *aneuploidy *euploidy *polyploidy

Homologous chromosomes: during anaphase I 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+

1) Addition of one or more sets of chromosomes (replication) 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 A B C D Crossover: 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