Meiosis: Defining Attributes Homologous chromosomes pair in
Prophase I Recombination occurs in Prophase I Homologs separate (“segregate”) in
Anaphase I
Prophase I Metaphase I Anaphase I
Meiotic chromosome dynamics
Prophase Metaphase I Anaphase I
Metaphase II Anaphase II
Meiosis ISegregates Homologous Chromosomes
Reductional Division2N to N
Meiosis II
Segregates Chromatids
Equational Division
1C
Meiosis II
Segregates Chromatids
Equational Division
1C
Meiosis I and II: Reductional and equational divisions
Mitosis (and Meiosis II): Sister centromere cohesion provides force to develop tension and align chromosomes at metaphase
Meiosis I: Homologs pair
Klug & Cummings, 6th Ed., 2000
Meiosis I: Homologs recombine
Hartl and Jones, 5th Ed., 2001
Meiosis I: Non-sister centromeres not associated; chiasmata and sister-chromatid cohesion provide force to develop tension and align homologous pairs of chromosomes at metaphase
DNA Synthesis & HomologousChromosome Pairing
Equational Division
ABCABCabcabcReductional DivisionABCABc abCabcABC ABc abC abc
abcABC
Meiosis I: Homologs separate
Hartl and Jones, 5th Ed., 2001
Random Metaphase I alignment leads to independent assortment
Hartl and Jones, 5th Ed., 2001
Meiosis II: Equational separation of chromatids
Hartl and Jones, 5th Ed., 2001
Meiotic error: Nondisjunction
Griffiths et al., 1999
Human Down syndrome: Trisomy 21
Nondisjunction of Chr 21 during meiosis leads to a gamete with an extra chromsome
Klug and Cummings, 6th Ed., 2000