1. Meiosis and Sexual Life Cycle Chapter 13

2. Heredity (inheritance) - transmission of traits from 1 generation to next. Variation - siblings differ from 1 another. Genetics - study of heredity and variation.

3. http://www.mssm.edu/genetics/fabry/images/figure1b.gif

4. Parents give offspring coded information - genes. Genes - segments of DNA. 4 nucleotides found in DNA create specific sequences determine traits. DNA in sperm and egg fuse together to create variation.

5. http://library.thinkquest.org/19037/media/basics/gene.GIF

6. Each chromosome has thousands of genes - located at specific spot - locus (loci).

7. http://www.cybered.net/library/Teaching_Resources/Biology/Evolution/Image_Gallery/Evolution-Loci.jpg

8. Asexual reproduction - 1 parent passes all genetic information on to offspring. Example: Hydra (eukaryotic) reproduce by budding cells produced by mitosis.

10. Sexual reproduction produces variation - combination of genes from parents unique. Siblings resemble each other because of similar genes.

11. Humans, somatic (non-sex) cells - 46 chromosomes. Each chromosome distinguished by size, position of centromere, by pattern of staining with certain dyes. Karyotype - picture of 23 pairs of chromosomes with centromeres and sizes. Chromosomes homologous - they have pair that matches them.

13. Sex chromosomes not homologous in male (X and Y) Females homologous (2 X’s). Other 22 pairs autosomes (non-sex chromosomes) 1 chromosome of pair inherited from each parent.

14. http://www.brooklyn.cuny.edu/bc/ahp/LAD/C9/graphics/C9_homologous_2.GIF

15. Each egg and sperm (gametes) have 22 autosomes, 1 sex chromosome. Haploid - half the # of chromosomes. Cells fuse (syngamy) - fertilization. Fertilized egg (zygote) has 2 haploid sets of chromosomes with genes from maternal and paternal family lines.

16. http://faculty.sulross.edu/ericsson/img0067b.jpg

17. When zygote has all chromosomes (46), - diploid. Humans - diploid # of chromosomes 46 (2n = 46). Gametes (develop in gonads) and are produced through meiosis - chromosome # halved. Fertilization and meiosis alternate in sexual life cycles.

19. Meiosis and fertilization timing varies among species. Fungi, some protists have 2 life cycles. Zygote starts off diploid, then divides to haploid. Haploid adult goes through mitosis.

20. Human life cycle

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22. Plants - alternation of generations. Includes haploid (gametophyte) and diploid (sporophyte) multicellular stages. Meiosis by sporophyte produces haploid spores - develop by mitosis into gametophyte.

24. Meiosis - 2 consecutive cell divisions (meiosis I, meiosis II) - result in 4 daughter cells. Each daughter cell - only ½ as many chromosomes as parent cell. Meiosis reduces chromosome # by copying chromosomes once, but dividing twice.

26. Meiosis I Stages are prophase, metaphase, anaphase, telophase. Interphase (preceding prophase) - chromosomes replicate to form sister chromatids. Single centrosome replicated.

28. Prophase I - chromosomes condense, homologous chromosomes pair up - form tetrads. Synapsis - proteins attach homologous chromosomes tightly together. Chromatids of homologous chromosomes cross (chiasmata), segments of chromosomes traded. Spindle forms from each centrosome.

30. Metaphase I - tetrads arranged at metaphase plate. Anaphase I - homologous chromosomes separate, pulled toward opposite poles.

32. Telophase I - movement of homologous chromosomes continues until haploid set at each pole. Each chromosome consists of linked sister chromatids. Cytokinesis - separates cytoplasm.

34. Prophase II - spindle apparatus forms, attaches to kinetochores of each sister chromatid, moves them around.

36. Metaphase II - sister chromatids arranged at metaphase plate. Anaphase II - centomeres of sister chromatids separate; travel toward opposite poles. Telophase II - separated sister chromatids arrive at opposite poles; nuclei form around chromatids.

38. Cytokinesis - cytoplasm separates; now 4 daughter cells.

40. Differences between mitosis and meiosis Chromosome # reduced by ½ in meiosis, not in mitosis. Mitosis produces 2 genetically identical cells; meiosis produces 4 unique ones.

41. http://ghr.nlm.nih.gov/handbook/illustrations/mitosismeiosis

42. Other differences 1 Crossing over: During prophase I, homologous chromosomes pair up (synapsis). At X-shaped regions (chiasmata) sections of nonsister chromatids exchanged.

43. http://www.synapses.co.uk/genetics/crosso1.gif

44. 2 Metaphase I homologous pairs of chromosomes, not individual chromosomes, aligned along metaphase plate. 3 Anaphase I - homologous chromosomes, (not sister chromatids) separate, carried to opposite poles of cell.

46. Contributions to Variation 1 Independent assortment - tetrads arrange themselves randomly on metaphase plate. Each homologous pair of chromosomes positioned independently of other pairs at metaphase I.

48. 2 Crossing over - homologous portions of 2 nonsister chromatids trade places. Crossing over begins early in prophase I as homologous chromosomes pair up gene by gene.

50. 3 Random fertilization - any sperm can fertilize any egg. Each egg sperm is 1 of 8 billion gene combinations - 70 trillion possibilities of combinations in zygote (doesn’t include crossing over)

51. http://www.itech.pjc.edu/fduncan/bsc1094/ap2c29ppt_files/slide0007_image008.jpg