Download
meiosis and sexual life cycle n.
Skip this Video
Loading SlideShow in 5 Seconds..
Meiosis and Sexual Life Cycle PowerPoint Presentation
Download Presentation
Meiosis and Sexual Life Cycle

Meiosis and Sexual Life Cycle

108 Vues Download Presentation
Télécharger la présentation

Meiosis and Sexual Life Cycle

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  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.jpghttp://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.

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

  10. 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.

  11. 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.

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

  13. 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.

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

  15. 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.

  16. 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.

  17. Human life cycle

  18. 11/28

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

  20. 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.

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

  22. 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.

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

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

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

  26. 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.

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

  28. 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.

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

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

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

  32. 2Metaphase I homologous pairs of chromosomes, not individual chromosomes, aligned along metaphase plate. • 3Anaphase I - homologous chromosomes, (not sister chromatids) separate, carried to opposite poles of cell.

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

  34. 2Crossing over - homologous portions of 2 nonsister chromatids trade places. • Crossing over begins early in prophase I as homologous chromosomes pair up gene by gene.

  35. 3Random 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)