BIOL 320 chp2set.ppt

CHROMATIN: EUCHROMATINHETEROCHROMATIN EUCHROMATIN & HETEROCHROMATIN

unduplicated chromosome duplicated chromosome NUCLEUS PREPARING TO DIVIDE CHROMOSOME DUPLICATION DNA REPLICATION S PHASE OF CELL CYCLE NUCLEUS DURING DIVISION RESTING (NONDIVIDING) CELL QUIESCENCE INTERPHASE DECONDENSATION CONDENSATION CHROMOSOMEAPPEARANCE

CENTROMERE TELOMERE q ARM p ARM

unduplicated chromosome duplicated chromosome Homologous pair of duplicated chromosomes Sister chromatids sister chromatids Sister chromatids non-sister chromatids Homologues

2n n n Mitosis Meiosis

unduplicated chromosome duplicated chromosome DNA Replication in anticipation of cell division

MitosisS Phase Meiosis IMeiosis II unduplicated chromosomeduplicated chromosome parental cell (somatic) daughter cells (somatic) parental cell (gonadal): “gonium” daughter cells (gonadal): “gametes”

Chromatin condensation Initial pairing of homologues Chromomeres appear Homology search begins Chromosomes shorten & thicken initial alignment, 300 nm Lateral elements appear Synaptonemal complex begins “bivalents,” duplicated but not apparent # bivalents = n Chromosomes shorten & thicken Synaptonemal complex developed b/w bivalents “synapsis,” 100 nm Bivalents resolve to “tetrads” Crossing over begins Crossing over apparent Sister chromatids separate Nonsister chromatids exchange “chiasmata” “Terminalization” begins Nonsister chromatids loosely attached Terminalization complete Nucleolus & nuclear envelope break down Centromeres are equatorial

Emerging Molecular Biology of Chromosome Junctioning and Nondisjunction

MitosisS Phase Meiosis IMeiosis II unduplicated chromosomeduplicated chromosome parental cell (somatic) daughter cells (somatic) parental cell (gonadal): “gonium” daughter cells (gonadal): “gametes”

CELL CYCLE and MEIOSIS

LEPTONEMA LEPTOTENE ZYGONEMA ZYGOTENE PACHYNEMA PACHYTENE DIPLONEMA DIPLOTENE DIAKINESIS