Mitosis
Mitosis (Animal Cells) After “S” phase replicates DNA Division of nucleus ONLY ! chromosome # stays constant Centromere divides each chromatid becomes a daughter chromosome M checkpoint-stops if chromosomes not aligned Prophase Metaphase Anaphase Telophase
Chromosome Number Each species has unique chromosome # no relationship to complexity Diploid--2n 2 copies of each chromosome (1/Mom & 1/Dad) (Homologous pairs) All somatic cells (body cells) are 2n Haploid--1n 1 copy of each chromosome (either Mom’s or Dad’s) Only gametes (sperm/eggs) are 1n
Chromosomes DNA replicates during “S” phase remains connected at centromere (Sister chromatids) Chromatin (DNA) wraps around histones (protein “balls”) * DNA/histone “complex” (nucleosome) supercoils chromosome Chromosomes-condensed rod- shaped DNA molecules during division
Chromatin!
6 ft of DNA in one microscopic cell = MESSY!!!
Histone + DNA = nucleosome
Nucleosomes coil around each other…..
…and keep coiling… (remember we have 6 whole feet of DNA to coil into a microscopic space!!!)
Until we get a Chromosome!!! This is actually 2 chromosomes! The original & the duplicated! We call this the replicated chromosome…made out of sister chromatids (exact copies) held together by a centromere.
Prophase 5 “events” everything gets ready to divide!! Chromatin coils chromosomes appear Nucleolus disappears Nuclear membrane disappears Centrioles & asters appear move to opposite poles of cell Spindle fibers appear Polar fibers centriole to centriole Kinetochore fibers centriole to centromere
Metaphase Kinetochore fibers push chromosomes to middle of cell
Anaphase Kinetochore fibers separate break centromeres pull chromatids to opposite poles of cell Characteristic “V” shape
Telophase Reverse of Prophase
Mitosis—Plant Cells Mitosis in plant cells Same phases as animal cells Plants don’t have centrioles or asters
Mitosis in Prokaryotes Asexual reproduction (Binary Fission) Cloning 2 identical daughter cells Single DNA strand duplicates cell elongates, pinches in half