Meiosis = cell division that reduces the number of chromosomes in half Meiosis 8.3 (p. 153-156) Meiosis = cell division that reduces the number of chromosomes in half Diploid number to haploid number Gametes = sex cells; have haploid number (male: sperm, female: egg) Like a double mitosis: PMAT I and PMAT II, with some key differences Diploid = Haploid =

Prophase I = homologous chromosomes pair up Meiosis 8.3 (p. 153-156) Prophase I = homologous chromosomes pair up Called synapsis; chromosome pairs called tetrads (tetra = 4) Crossing-over = chromatids swap genes; happens sometimes causing genetic variation Genetic recombination = new mix of genes from crossing-over

Metaphase I = tetrads line up along the equator Meiosis 8.3 (p. 153-156) Metaphase I = tetrads line up along the equator Homologous pairs line up next to each other Key difference

Anaphase I = homologous chromosomes move to opposite poles Meiosis 8.3 (p. 153-156) Anaphase I = homologous chromosomes move to opposite poles Big difference: each chromosomes still has 2 chromatids That is the centromeres don’t split

Meiosis 8.3 (p. 153-156) Telophase I = 2 cells separate, but now each cell has haploid number of chromosomes

Single chromatid is not copied during an interphase stage Meiosis 8.3 (p. 153-156) PMAT II = looks very much like mitosis but at the end it has haploid number (1n) Single chromatid is not copied during an interphase stage Instead these gametes will match up chromatids when they fuse with another sex cell Zygote = sperm and egg fused to form new cell again with diploid number (2n)

Offspring is genetically unique Meiosis 8.3 (p. 153-156) Sexual reproduction = reproduction by forming a zygote (male and female) Offspring is genetically unique Asexual reproduction = reproduction from one parent By binary fission or mitosis only, no meiosis Offspring is genetically identical to parent