1. 1 Types of Cell Reproduction Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Mitosis & binary fission are examples of asexual reproduction Mitosis & binary fission are examples of asexual reproduction Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells Meiosis is an example Meiosis is an example copyright cmassengale

2. 2 Review of Mitosis copyright cmassengale

3. 3 Interphase Prophase Metaphase Anaphase Telophase Mitotic Stages: Metaphase plate Cleavage Furrow copyright cmassengale

4. 4 Eukaryotic Cell Division Used for growth and repair Used for growth and repair Produce two new cells identical to the original cell Produce two new cells identical to the original cell Cells are diploid (2n) Cells are diploid (2n) Chromosomes during Metaphase of mitosis ProphaseMetaphase Anaphase Telophase Cytokinesis copyright cmassengale

5. 5 Mitosis Animation Name each stage as you see it occur? copyright cmassengale

6. 6 Locate the Four Mitotic Stages in Plants Metaphase Prophase Anaphase Telophase copyright cmassengale

7. 7 Uncontrolled Mitosis If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins increase the chance that a normal cell develops into a tumor cell Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells copyright cmassengale

8. 8 Meiosis Formation of Gametes (Eggs & Sperm) copyright cmassengale

9. 9 Facts About Meiosis Preceded by interphase which includes chromosome replication Preceded by interphase which includes chromosome replication Two meiotic divisions --- Meiosis I and Meiosis II Two meiotic divisions --- Meiosis I and Meiosis II Called Reduction- division Called Reduction- division Original cell is diploid (2n) Original cell is diploid (2n) Four daughter cells produced that are monoploid (1n) Four daughter cells produced that are monoploid (1n) copyright cmassengale

10. 10 Facts About Meiosis Daughter cells contain half the number of chromosomes as the original cell Daughter cells contain half the number of chromosomes as the original cell Produces gametes (eggs & sperm) Produces gametes (eggs & sperm) Occurs in the testes in males (Spermatogenesis) Occurs in the testes in males (Spermatogenesis) Occurs in the ovaries in females (Oogenesis) Occurs in the ovaries in females (Oogenesis) copyright cmassengale

11. Remember: FSH-follicle stimulating hormone regulated by Pituitary gland regulates meiosis in egg and sperm. Case study: Eric- dr’s removed his damaged Pituitary gland. So a side effect would be low sperm count. He still produced testosterone bc that is regulated by testes. copyright cmassengale11

12. 12 Start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) Occurs in our germ cells that produce gametes-NOT SOMATIC More Meiosis Facts copyright cmassengale

13. 13 Why Do we Need Meiosis? It is the fundamental basis of sexual reproduction-more genetic variation It is the fundamental basis of sexual reproduction-more genetic variation Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote copyright cmassengale

14. 14 Fertilization – “Putting it all together” 1n =3 2n = 6 copyright cmassengale

15. 15 Replication of Chromosomes Replication is the process of duplicating a chromosome Replication is the process of duplicating a chromosome Occurs prior to division-”S phase” Occurs prior to division-”S phase” Replicated copies are called sister chromatids Replicated copies are called sister chromatids Held together at centromere Held together at centromere Occurs in Interphase copyright cmassengale

16. 16 A Replicated Chromosome Homologs Homologs (same genes, different alleles) (same genes, different alleles) Sister Chromatids (same genes, same alleles) Gene X Homologs separate in meiosis I and therefore different alleles separate. copyright cmassengale

17. 17 Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number Fertilization then restores the 2n number from momfrom dadchild meiosis reduces genetic content too much! The right number! copyright cmassengale

18. 18 Meiosis: Two Part Cell Division Homologsseparate Sisterchromatidsseparate Diploid Meiosis I Meiosis II Diploid Haploid copyright cmassengale

19. 19 Meiosis I: Reduction Division Nucleus Spindlefibers Nuclearenvelope Early Prophase I (Chromosome number doubled) Late Prophase I Metaphase I Anaphase I Telophase I (diploid) copyright cmassengale

20. 20 Prophase I Early prophase Homologs pair. Homologs pair. Crossing over occurs Crossing over occurs. Late prophase Chromosomes condense. Chromosomes condense. Spindle forms. Spindle forms. Nuclear envelope fragments. Nuclear envelope fragments. copyright cmassengale

21. Can crossover occur between 2 different chromosomes? Yes, but scientists refer to this as a mutation. copyright cmassengale21

22. 22 Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids) Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Process Called Synapsis copyright cmassengale

23. 23 Crossing-Over Homologous chromosomes in a tetrad cross over each other Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring Produces Genetic recombination in the offspring copyright cmassengale

24. 24 Homologous Chromosomes During Crossing-Over copyright cmassengale

25. 25 Crossing-over multiplies the already huge number of different gamete types produced by independent assortment Crossing-Over copyright cmassengale

26. 26 Metaphase I Homologous pairs of chromosomes align along the equator of the cell copyright cmassengale

27. 27 Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres attached at their centromeres. copyright cmassengale

28. 28 Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale

29. 29 Meiosis II Only one homolog of each chromosome is present in the cell Only one homolog of each chromosome is present in the cell. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Sister chromatids carry identical genetic information. Gene X copyright cmassengale

30. 30 Meiosis II: Reducing Chromosome Number Prophase II Metaphase II Anaphase II Telophase II 4 Genetically Different haploid cells copyright cmassengale

31. 31 Prophase II Nuclear envelope fragments. Spindle forms. copyright cmassengale

32. 32 Metaphase II Chromosomes align along equator of cell. copyright cmassengale

33. 33 Anaphase II Sister chromatids separate and move to opposite poles Sister chromatids separate and move to opposite poles. Equator Pole copyright cmassengale

34. 34 Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale

35. 35 Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome copyright cmassengale

36. 36 Meiosis Animation copyright cmassengale

37. 37 Comparing Mitosis and Meiosis copyright cmassengale

38. 38 MitosisMeiosis Number of divisions 12 Number of daughter cells 24 Genetically identical? YesNo Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction Comparison of Divisions copyright cmassengale