1. Meiosis and Sexual Life Cycles

2. Transmission of Traits
Based on heredity, where specific genes are passed on to offspring via chromosomes (or DNA)
Gametes transmit these chromosomes (or DNA) to the next generation in plants and animals

3. Asexual and Sexual Reproduction
Asexual reproduction will result in offspring that are exact copies of the one parent produced via mitosis
The ‘child’ would be a clone of the parent
Sexual reproduction allows for genetic variability because the offspring is a combination of both parents
Both of these have reproduced asexually

4. Inheritance and Cells
Normal somatic cells in humans will have 23 pairs of chromosomes or 46 chromosomes
22 pairs or 44 chromosomes will be autosomes
1 pair or 2 will be sex chromosomes
Can be XX or XY (normally)
We inherit one chromosome in each pair from each parent
Karyotype showing the homologous pairs of chromosomes in an individual

5. Diploid and Haploid
We will receive 23 chromosomes from our mother and 23 from our father.
Counting one of those sets (or 23 chromosomes in humans) is called n or haploid.
Counting both of those sets is 2n or diploid
In a cell that has completed S phase, the chromosome number has not changed; however, DNA has been replicated and each chromosome has a sister chromatid

6. Fertilization and Growth
Sperm (n) will fertilize an egg (n) creating an offspring (2n)
All cells in the body will be 2n (and undergo mitosis) except for the gametes which will be produced by germ cells in the gonads (and undergo meiosis)

7. Variation in Life Cycles
Normal animal sexual life cycle (same as seen in humans)

8. Variation in Life Cycles
Plants and some algae undergo Alternation of Generations
Diploid and haploid stages are both multicellular
Diploid stage is called Sporophyte
Gives rise to a haploid spore which divides via mitosis
Haploid stage is called gametophyte
Gives rise to a gamete which fuses with another creating a diploid zygote

9. Variation in Life Cycles
Occurs in most fungi and some protists (including some algae)
Gametes fuse, forming a diploid zygote. Meiosis occurs producing haploid cells (not gametes) which then divide via mitosis
Can give rise to either unicellular descendents or multicellular haploid adult organisms
Further mitosis will give rise to gametes

10. Meiosis
Begins with one diploid cell which goes through two stages (Meiosis I and Meiosis II) to end up with four genetically different haploid cells
Begins similarly to mitosis with Interphase

11. Prophase I
Chromosomes condense, homologs pair up gene by gene in synapsis, allowing crossing over to occur
Synapsis ends in mid-prophase, allowing homologs to move apart slightly; homologs are still attached at chiasmata
The remainder of prophase I occurs much like prophase in mitosis

12. Metaphase I
Homologous chromosomes line up at the metaphase plate, one chromosome in each pair is facing each pole
Sister chromatids remain together

13. Anaphase I
Proteins responsible for attachment of homologous chromosomes breakdown
Homologous chromosomes are pulled to opposite sides of the cell

14. Telophase I & Cytokinesis
Two haploid cells form, but each chromosome still has an attached sister chromatid
No DNA replication occurs prior to Meiosis II

15. Meiosis I

16. Prophase II
Spindle forms and prophase progresses similarly to mitosis

17. Metaphase II Chromosomes line up on the metaphase plate
All kinetochores attach to spindle fibers

18. Anaphase II Proteins holding sister chromatids together breakdown
Sister chromatids move to opposite sides of the cell

19. Telophase II & Cytokinesis
Nuclei form, chromosomes decondense and cytokinesis occurs
One Meiotic division produces four genetically different haploid daughter cells

20. Meiosis II

21. Meiosis vs. Mitosis

22. Genetic Variation Genetic variation in meiosis arises via
Independent assortment of chromosomes
Crossing over
Random fertilization