1. Meiosis

2. Chromosome and Meiosis
2 groups of specialized cells
Germ cells and somatic cells
Somatic cells make up most of your body tissues and organs
Germ cells—cells in reproductive organs that develop into gametes.
Gametes—sex cells
DNA passed to children

3. Haploid and Diploid Body cells—diploid Gametes-haploid
2 copies of each chromosome—1 from mother, 1 from father 2n
In humans, 2n chromosome is number 46
Gametes-haploid N
Only one copy of each chromosome.

4. Autosomes and Sex Chromosomes
23 from mother, 23 from father
Each pair together—homologous chromosomes
Chromosome pairs 1-22 are referred to autosomes
Chromosome 23—sex chromosomes

5. Sex Chromosomes X and Y XY system determines the sex of offspring
XX—female
XY—male
Make up pair 23
X is larger sex chromosome—numerous genes
Y contains genes the direct the development of testes and other male traits.

6. Meiosis Homologous chromosomes—2 SEPARATE chromosomes
One from mother, one from father
Same length and carry the same genes
NOT COPIES OF EACH OTHER
Divided in meiosis I
Sister Chromatids—each half of a duplicated chromosome
Attached by centromere
Divided in Meiosis II and mitosis

7. Meiosis
Germ cells in reproductive organs undergo the process of meiosis to form gametes
Form of nuclear division that divides a diploid cell into haploid
Reduction division
DNA is copied once but divided twice

8. Meiosis I DNA is already copied b/4 meiosis can begin
Produces 2 haploid cells with duplicated chromosomes

9. Chromosomes coil to become shorter and thicker
Duplicated homologous chromosomes pair and crossing over occurs
Gives rise to genetic recombination
Homologous pair is a tetrad
Crossing over of nonsister chromatids
Nucleolus and nucleus disappear
Longest stage of meiosis

11. Crossing-Over and Genetic Recombination

12. Metaphase I Centrioles at opposite poles
Homologous pairs arrange down center of cell
Spindle fibers from one pole attach to one chromosome of each pair and spindle fibers from the other pole attach to the other chromosome

13. Anaphase I
Begins when the two chromosomes of each tetrad separate and move toward opposite poles of the cell
Sister chromatids stay intact

14. Telophase I Haploid set of duplicated chromosomes in each new cell
Nuclear envelope reforms around each set, spindle fibers disappear and cytokinesis follows
Sometimes chromosomes decondense—but not always (in rapid meiotic cells)

16. Meiosis I

17. Meiosis II Divides sister chromatids Results in undoubled chromosomes
DNA is not copied again

18. Prophase II Centrioles duplicate and begin to move to opposite poles
Nuclear membrane breaks apart
Spindle fibers begin to form

20. Single, duplicated chromosomes align down center of the cell
Spindle fibers attach to centromere of each sister chromatid pair

21. Anaphase II
Sister chromatid separate and are pulled to opposite poles of the cell

22. Telophase II Nuclear envelope forms around each set of chromosomes
Cytokinesis takes place
Produces 4 daughter cells (gametes) with haploid set of chromosomes
No two cells are the same

25. Meiosis II

26. Haploid Cells develop into mature gametes
End result: Haploid cells (n)
Incapable of fertilization until they go through more changes
Gametogenisis—production of gametes
Meiosis and other changes to produce a mature cell

27. Gametogenesis Male gamete—sperm, much smaller than female
Female gamete—egg
Sperm—contributes DNA
Egg—contributes DNA, organelles, molecular building blocks, and other materials an embryo needs to begin life.
1 of 4 cells produces in meiosis makes an egg
Polar Bodies—cells with little more than DNA that are eventually broken down.
Do not undergo meiosis II

28. Fertilization
Sexual Reproduction involves fusion of gametes. Offspring that are a genetic mixture of both parents.
Fertilization—fusion of egg and sperm
Nuclei of egg and sperm fuse to form one nucleus.
Must have correct number of chromosomes for a healthy new organism to develop.

29. Mitosis vs. Meiosis

30. Mitosis vs Meiosis