Mechanisms of Evolution Concept 3: Analyzing meiosis and sexual life cycles as a mechanism for genetic variation Campbell – Ch 13 Holtzclaw: pg. 97-103

Meiosis and Sexual Life Cycles You must know: The differences between asexual and sexual reproduction The role of meiosis and fertilization in sexually reproducing organisms The importance of homologous chromosomes to meiosis How the chromosome number is reduced from diploid to haploid through the stages of meiosis Three important differences between mitosis and meiosis The importance of crossing over, independent assortment, and random fertilization to increasing genetic variability

Meiosis and Sexual Life Cycles Vocabulary: Gene Locus Allele Nonhomologous chromosome Homologous chromosome Chromatid Sex Chromosome Autosome Somatic Cells Gametes Haploid (n) Diploid (2n) Daughter cells Zygote Synapsis Tetrad Chiasmata Meiosis I Meiosis II Fertilization Crossing over Independent Assortment Random Fertilization

0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome Fig. 12-4 0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Figure 12.4 Chromosome duplication and distribution during cell division Separation of sister chromatids Centromere Sister chromatids

Mitosis Animation Mitosis under the Microscope Meiosis Animation

Try This! Mitosis Meiosis Chromosome # in Parent Cells Number of DNA Replications Number of Divisions Number of Daughter Cells Produced Chromosome Number of Daughter Cells Purpose/Function

Try This! How are Meiosis I and II different?

Genetic Variation Most genetic variation in a population is due to sexual recombination of alleles

Genetic Variation The Shuffling of Alleles... Three mechanisms: Crossing Over (meiosis I – prophase I) Independent Assortment (meiosis I – prophase I) Fertilization