Mitosis Meiosis Mitosis n n One cell divides

Mitosis + Meiosis

Mitosis n n One cell divides to make two genetically identical (diploid) cells Five stages: Interphase n Prophase n Metaphase n Anaphase n Telophase n Mnemonics: § I. P. MAT § upside-down TAMPI

Interphase n “Resting” period between cell divisions n Chromosomes replicate n Centrioles lie outside the nucleus, next to each other

Prophase n Chromosomes condense n Each chromosome is two identical chromatids n Spindles begin to form from the centrioles n Nuclear envelope fragments and disperses

Late Prophase (also known as Prometaphase) n n n Centrioles move to opposite ends of the cell Spindle fibers from both centrioles attach to each chromosome Each centriole is attached to 46 chromosones

Metaphase n n Chromosomes line up on metaphase plate Fibers begin to tug each chromosome toward opposite ends of the cell

Anaphase n Fibers pull chromatids toward opposite ends of the cell

Telophase n n Chromatids (now considered chromosomes) arrive at opposite ends of the cell New nuclear membranes form

Cytokinesis n Movement (kinesis) of the cytoplasm (cyto) n Rest of the cell divides n Two genetically identical cells formed

Meiosis n n One cell divides to make four genetically different haploid cells Ten stages: Interphase I n Prophase I n Metaphase I n Anaphase I n Telophase I n Interphase II n Prophase II n Metaphase II n Anaphase II n Telophase II n

Interphase I n Same as Mitosis n Chromosomes replicate n Centrioles lie outside the nucleus

Prophase I n Same as in Mitosis, except chromosomes attach to nucleus in homologous pairs n “Crossing over” occurs

“Crossing Over” (not that show with John Edward) n Homologous pairs exchange sections of DNA n This can cause alleles to be separated

Late Prophase I (also known as Prometaphase I) n Same as Mitosis, except spindle fibers from each centriole attach to one chromosome of a homologous pair n Each centriole is attached to 23 chromosones

Metaphase I n Same as Mitosis, except homologous pairs line up on either side of the metaphase plate

Anaphase I n Homologous pairs separate n Chromatids do not separate

Telophase I n n Chromosones move towards the ends of the cell New nuclear membranes form

Cytokinesis I n Same as Mitosis

Interphase II n Unlike in Mitosis, Chromosones do not replicate n (already replicated)

Prophase II n n Chromosomes condense Spindles form and separate Nuclear membrane fragments and disperses No crossing over

Late Prophase II (also known as Prometaphase II) n n Centrioles move to opposite ends of the cell Both sides attach spindle fibers to chromosones

Metaphase II n Chromosomes align along the metaphase plate n Chromosones split into chromatids and pulled to both ends

Anaphase II n Fibers pull chromatids apart and towards opposite ends of the cells

Telophase II n Chromatids arrive at either end of each cell and new nuclear membranes form

Cytokinesis II n n Rest of the cells divide Four genetically different cells formed

Images taken from: http: //www. pbs. org/wgbh/nova/miracle/divi_text. html http: //www. accessexcellence. org/RC/VL/GG/crossing. php http: //www. johnedwardaustralia. com/pictures. htm