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

2. 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

3. 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

4. 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

5. Mitosis Animation Mitosis under the Microscope
Meiosis Animation

6. 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

7. Try This!
How are Meiosis I and II different?

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

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