Download Meiosis and Binary Fission Notes

Meiosis and Binary Fission Notes
January 19­20, 2012
1/19 (R) Meiosis (textbook pages 270­276)
Purpose : produce haploid gametes
Chromosomes/Chromosome Number
• humans have 46 chromosomes (23 pairs)
• Gene ­ DNA segments carry instructions for traits (characteristics) and cell function
Pair of Homologous Chromosomes
same location of genes for specific traits
centromere
male
female
Haploid and Diploid Cells
• Gamete ­ sex cells with 1/2 number of chromosomes
• Haploid ­ cell with n # of chromosomes
• Diploid ­ cell with 2n # of chromosomes (n from male, n from female)
• Fertilization ­ 1 haploid gamete combines with another haploid gamete to form a diploid organism
Meiosis and Binary Fission Notes
January 19­20, 2012
MEIOSIS I
• produces gametes
• reduces # of chromosomes
**mitosis keeps same # chromosomes
**meiosis reduces # chromosomes by 1/2
Stages of meiosis I
• Interphase
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Cytokinesis
Interphase
• DNA replicates
• protein synthesis
Prophase I
• replicated chromosomes visible sister chromatids
• homologous chromosomes condnese to for pairs in process called synapsis
centromere
sister chromatids
Meiosis and Binary Fission Notes
January 19­20, 2012
**Crossing over ­ chromosome segments exchange between homologous chromosome pairs
• centrioles move to opposite sides (poles)
• spindle fibers form, bind to sister chromatids at centromere
Metaphase I
• homologous chromosome pairs line up at equator
**mitosis ­ individual chromosomes line up
**meiosis ­ paired chromosomes line up
Meiosis and Binary Fission Notes
January 19­20, 2012
1/20 (F)
Anaphase I
• chromosomes separate
• chromosome # reduces from 2n to n
**mitosis ­ sister chromatids split
**meiosis ­ homologous chromosome pairs split (still have 2 sister chromatids)
Telophase I
• poles contain 1/2 of chromosome pair
**sister chromatids NOT identical because of crossing over
Cytokinesis
• cytoplasm splits
• cells go to Meiosis II
**meiosis only HALF completed
**have 2 diploid cells which are not genetically identical
MEIOSIS II
Interphase
• DNA does NOT replicate
Prophase II
• chromosomes condense
• spindle fibers form
Meiosis and Binary Fission Notes
January 19­20, 2012
Metaphase II
• diploid chromosomes line up at equator
**mitosis ­ haploid chromosomes line up
Anaphase II
• sister chromatids pulled apart, move to poles
Telophase II
• chromosomes reach poles (haploid)
• nuclei & nuclear membrane reappear
Cytokinesis
• cytoplasm divides
**Mitosis produces 2 genetically identical diploid cells
**Meiosis produces 4 genetically DIFFERENT haploid cells
Genetic Variation
occurs during : meiosis
crossing over
fertilization
Meiosis and Binary Fission Notes
January 19­20, 2012
Binary Fission (textbook page 520)
• division of a cell into 2 genetically identical cells
• chromosomes replicate
• new copies separate
• cell elongates (gets longer)
• new plasma membrane and cell wall form to separate cell into 2 identical cells
• 1 bacterium can become 1 billion bacteria in 10 hours (in ideal situation)
chromosomes
cytoplasm
cell plasma wall membrane