MEIOSIS Making gametes…

Recall… CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS REPRODUCE

MITOSIS CREATES DIPLOID BODY CELLS Makes 2 cells genetically identical to parent cell & to each other Used by organisms to: increase size of organism, repair injuries, replace worn out cells http://waynesword.palomar.edu/lmexer2a.htm

MEIOSIS CREATES HAPLOID SEX CELLS Makes 4 cells genetically different from parent cell & from each other Used for sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm

Stages of Meiosis

Meiosis

Meiosis takes place in two series of steps Meiosis I I, P, M, A, T + Meiosis II P, M, A, T Which means…no DNA replication before meiosis II No second “I”

Interphase I DNA replicates creating homologous chromosomes

HOMOLOGOUS CHROMOSOMES SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

PROPHASE I Homologous chromosomes pair up to form a TETRAD (4 chromatids) Images modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

Homologous pairs exchange DNA 2. CROSSING OVER Homologous pairs exchange DNA After crossing over, chromatid arms are NOT IDENTICAL anymore http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

Metaphase I Tetrads line up in the middle

Anaphase I- Tetrads pull apart to opposite ends of the cell.

Telophase I- Cell separates into two new cells

No Interphase II which means chromosomes are NOT copied again. Meiosis II No Interphase II which means chromosomes are NOT copied again.

Prophase II ~ TWO cells begin meiosis II

Metaphase II chromosomes line up in the middle of the cell

Anaphase II -chromosomes are pulled to opposite ends of the cell

Telophase II / Cytokinesis ~ The two cells divide to form 4 genetically different cells (gametes)

End Result of Meiosis Four new cells Half # chromosomes as parent cell - haploid (n) Making of gametes

End Result of Mitosis TWO new cells SAME # chromosomes as parent cell - diploid (2n) Repair or Replace cells

Meiosis Video