1. meiosis

2. Sexual reproduction Cell division that produces gametes Vocabulary
Allows for variation through recombination and crossing over
Vocabulary
Genes- instructions for specific traits located on DNA
Gametes – sex cells (sperm and egg)
Most DNA is in sperm and egg (some may be located in mitochondria or chloroplasts)
Somatic cells- body cells
Chromosomes are long strands of coiled DNA which have hundreds to thousands of genes (each with a specific nucleotide sequence)
Loci – the gene location on the chromosome

3. More vocabulary
Karyotype- a picture of paired condensed chromosomes (chromosomes are paired based on length, centromere location and pattern)
Homologous- matching chromosomes (genes will be at the same loci of each chromosome)
Alleles – genes located at the same loci (but they may have variation; ex. Brown eye color and blue eye color)
Sex Chromosomes – X and Y chromosomes (in humans that is chromosome 23)
Autosome – non sex chromosomes (1-22)

4. Alternative life cycles
Fungi/some algae
meiosis produces 1N cells that divide by mitosis to produce 1N adults (gametes by mitosis)
Plants/some algae
Alternation of generations:
2N sporophyte (diploid) produces 1N (haploid) spores, by meiosis
spore divides by mitosis to generate a 1N gametophyte
gametes then made by Gametophyte mitosis which then fertilize into 2N sporophyte

6. Meiosis stages

7. Prophase I (1 cell )
Nucleus disappears, spindle fibers form, and the chromatid pairs visible.
Chromatid pairs find their homologous pair, forming a tetrad (bivalent).
Homologous chromosomes are 2 of the same type of chromosomes.
Crossing over - 2 homologous chromosomes switch pieces of DNA.
Chiasma site of crossing over

8. A little more on prophase 1
Cohesins hold sister chromatids together
At specific points along non sister chromatids, DNA is broken
A synaptonemal complex holds the homologous chromatids tight to one another (synapsis)
DNA is reattached but to the non- sister chromatid
Chiasmata are visible

9. Metaphase I (1 cell ) Tetrads meet at the middle of the cell.
One pair faces each pole

10. Anaphase I (1 cell ) The tetrads split apart
Homologous chromosomes split moving toward opposite poles
Chromatids move as a unit

11. Telophase I and Cytokinesis (2 cells )
Two cells form
Each have a full set of chromosomes as chromatid pairs.
Two haploid daughter cells
Cleavage furrow or Cell Plate form

12. Prophase II (2 cells ) Spindle Fiber forms
Chromatid pairs continue moving to the center of the cell.

13. Metaphase II (2 cells )
The chromatid pairs meet at the middle. (Similar to Mitosis)
Chromosomes are not genetically identical (due to crossing over in Meiosis 1)

14. Anaphase II (2 cells )
The chromatid pairs split apart.

15. Telophase II and Cytokinesis (4 cells)
Each of the two cells split making a total of 4 cells.
Each cell contains 1/2 the normal number of chromosomes.
Humans-
Spermatogenesis – 4 sperm cells
Oogenesis- 1 egg and 3 polar bodies

16. Meiosis benefits Genetic Variation DNA Backup and Repair
Increased Biodiversity
Disease Resistance
DNA Backup and Repair
Backup copy of instructions in case one is not correct
Recombination process can repair DNA

17. Origins of Genetic Variation, I
Independent assortment: homologous pairs of chromosomes position and orient randomly (metaphase I) and nonidentical sister chromatids during meiosis II
Combinations possible:
2n (n the haploid number of the organism)

18. Origins of Genetic Variation, II
Crossing over (prophase I):
the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes)
Random fertilization:
1 sperm (1 of 8 million possible chromosome combinations) x 1 ovum (1 of 8 million different possibilities) = 64 trillion diploid combinations!

19. Meiosis mistakes Non disjunction Translocation/Inversion/Deletion
Some forms of leukemia
Non disjunction
Chromatids fail to separate in either anaphase 1 or 2
Resulting in an extra chromosome
Tuner Syndrome XXX
Kleinfelder's Syndrome XXY
Downs Syndrome (Trisomy 21)

20. https://upload. wikimedia

21. Cyclin – protein that activates enzymes to initiate replication
Growth Factors – proteins that bind to plasma membrane receptors and trigger mitosis (can be hormones)
Hormones – Steroid hormones bind to DNA via nuclear hormone receptor proteins
Cyclin – protein that activates enzymes to initiate replication
Stimulates transcription and replication factors
Ras Cyclin – verifies cell is proper size
Ensures cells have time to grow and differentiate
P53 – Tumor Suppressor Protein checks DNA for damage before replication
Stops cell cycle if DNA is damaged
Many cancers associated with a defective p53 gene
MAD1 – Verifies spindles attach to kinetochore
Ensures proper distribution of chromosomes to daughter cells