Biology lecture 7


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  • Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.
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  • Fusion of gametes to produce zygote In humans this takes place near the top of the oviduct . Hundreds of sperm reach the egg (shown in this photo). When a sperm reaches the ovum cell the two membranes fuse and the sperm nucleus enters the cytoplasm of the ovum. This triggers a series of reactions in the ovum that cause the jelly coat to thicken and harden, preventing any other sperm from entering the ovum. The sperm and egg nuclei then fuse, forming a diploid zygote. In plants fertilisation takes place in the ovary at the base of the carpel. The haploid male nuclei travel down the pollen tube from the pollen grain on the stigma to the ovules in the ovary. In the ovule two fusions between male and female nuclei take place: one forms the zygote (which will become the embryo) while the other forms the endosperm (which will become the food store in the seed). This double fertilisation is unique to flowering plants
  • Biology lecture 7

    1. 1. Reproduction Lecture-7 copyright cmassengale
    2. 2. Reproduction Sexual Reproduction Asexual Reproduction
    3. 3. Two Types of Reproduction <ul><li>Asexual Reproduction </li></ul><ul><li>Involves a single organism or cell </li></ul><ul><li>Cell divides </li></ul><ul><li>Offspring IDENTICAL to parent </li></ul>copyright cmassengale
    4. 4. Identical Daughter Cells Parent Cell Two identical daughter cells copyright cmassengale
    5. 5. Types of Asexual Reproduction <ul><li>Mitosis - is the exact duplication of the nucleus of a cell so as to form two identical nuclei during cell division. </li></ul>
    6. 6. Types of Asexual Reproduction <ul><li>2 . Binary Fission - occurs in one-celled organisms such as the ameba and paramecium. The nucleus divides by mitosis and the cytoplasm divides, forming 2 new daughter cells of equal size. </li></ul>
    7. 7. Cell Division in Prokaryotes <ul><li>Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission </li></ul><ul><li>Single chromosome makes a copy of itself </li></ul><ul><li>Cell wall forms between the chromosomes dividing the cell </li></ul>Parent cell 2 identical daughter cells Chromosome replicates Cell splits copyright cmassengale
    8. 8. Animation of Binary Fission copyright cmassengale
    9. 9. Types of Asexual Reproduction <ul><li>3. Budding - Occurs in Hydra and yeast. The division of cytoplasm is unequal so one of the daughter cells is larger than the other. The daughter cells can separate or remain attached. </li></ul>
    10. 10. Types of Asexual Reproduction <ul><li>4. Sporulation - occurs in molds, mosses, etc </li></ul><ul><li>Spores are produced in large numbers by mitosis. </li></ul><ul><li>Spores are surrounded by a tough coat to help them survive harsh environmental conditions. </li></ul>
    11. 11. Types of Asexual Reproduction <ul><li>5. Regeneration - Refers to the replacement or regrowth of lost or damaged body parts </li></ul>
    12. 12. Regeneration… <ul><li>This refers to the ability of some animals to re-grow severed parts. </li></ul><ul><li>Some of these animals can also grow new organisms from the severed pieces (Segmented Worms and Sea Stars) </li></ul>
    13. 13. Types of Asexual Reproduction <ul><li>6. Vegetative Propagation – </li></ul><ul><li>Occurs only in plants (vegetative). New plants develop from the roots, stems, or leaves of the parent plant. </li></ul>
    14. 14. Parthenogenesis… <ul><li>Offspring can arise from unfertilized eggs. </li></ul><ul><li>Includes some Fish, Reptiles, Amphibians and Aphids. </li></ul><ul><li>Most of these species can switch between Sexual and Asexual Reproduction. </li></ul><ul><li>(depending on conditions) </li></ul>
    15. 15. Two Types of Reproduction <ul><li>Sexual Reproduction </li></ul><ul><li>Involves 2 parents </li></ul><ul><li>Egg fertilized by sperm to make a ZYGOTE </li></ul><ul><li>Offspring DIFFERENT from parents </li></ul><ul><li>Meiosis is an example </li></ul>copyright cmassengale
    16. 16. Meiosis Formation of Gametes (Eggs & Sperm) copyright cmassengale
    17. 17. Facts About Meiosis <ul><li>Preceded by interphase which includes chromosome replication </li></ul><ul><li>Two meiotic divisions --- Meiosis I and Meiosis II </li></ul><ul><li>Called Reduction- division </li></ul><ul><li>Original cell is diploid (2n) </li></ul><ul><li>Four daughter cells produced that are monoploid (1n) </li></ul>copyright cmassengale
    18. 18. Facts About Meiosis <ul><li>Daughter cells contain half the number of chromosomes as the original cell </li></ul><ul><li>Produces gametes (eggs & sperm ) </li></ul><ul><li>Occurs in the testes in males ( Spermatogenesis ) </li></ul><ul><li>Occurs in the ovaries in females ( Oogenesis ) </li></ul>copyright cmassengale
    19. 19. More Meiosis Facts <ul><li>Start with 46 double stranded chromosomes (2n) </li></ul><ul><li>After 1 division - 23 double stranded chromosomes (n) </li></ul><ul><li>After 2nd division - 23 single stranded chromosomes (n) </li></ul><ul><li>  Occurs in our germ cells that produce gametes </li></ul>copyright cmassengale
    20. 20. Why Do we Need Meiosis? <ul><li>It is the fundamental basis of sexual reproduction </li></ul><ul><li>Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote </li></ul>copyright cmassengale
    21. 21. Fertilization – “Putting it all together” 1n =3 2n = 6 copyright cmassengale
    22. 22. Replication of Chromosomes <ul><li>Replication is the process of duplicating a chromosome </li></ul><ul><li>Occurs prior to division </li></ul><ul><li>Replicated copies are called sister chromatids </li></ul><ul><li>Held together at centromere </li></ul>Occurs in Interphase copyright cmassengale
    23. 23. A Replicated Chromosome Gene X Homologs separate in meiosis I and therefore different alleles separate. copyright cmassengale Homologs (same genes, different alleles) Sister Chromatids (same genes, same alleles)
    24. 24. Meiosis Forms Haploid Gametes <ul><li>Meiosis must reduce the chromosome number by half </li></ul><ul><li>Fertilization then restores the 2n number </li></ul>The right number! copyright cmassengale from mom from dad child meiosis reduces genetic content too much!
    25. 25. Meiosis: Two Part Cell Division Homologs separate Sister chromatids separate Diploid Diploid Haploid copyright cmassengale Meiosis I Meiosis II
    26. 26. Meiosis I: Reduction Division Early Prophase I (Chromosome number doubled ) Late Prophase I Metaphase I Anaphase I Telophase I (diploid) copyright cmassengale Nucleus Spindle fibers Nuclear envelope
    27. 27. Prophase I <ul><li>Early prophase </li></ul><ul><li>Homologs pair. </li></ul><ul><li>Crossing over occurs . </li></ul><ul><li>Late prophase </li></ul><ul><li>Chromosomes condense. </li></ul><ul><li>Spindle forms. </li></ul><ul><li>Nuclear envelope fragments. </li></ul>copyright cmassengale
    28. 28. Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids)   Join to form a TETRAD Called Synapsis copyright cmassengale
    29. 29. Crossing-Over <ul><li>Homologous chromosomes in a tetrad cross over each other </li></ul><ul><li>Pieces of chromosomes or genes are exchanged </li></ul><ul><li>Produces Genetic recombination in the offspring </li></ul>copyright cmassengale
    30. 30. Homologous Chromosomes During Crossing-Over copyright cmassengale
    31. 31. Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment copyright cmassengale
    32. 32. Metaphase I Homologous pairs of chromosomes align along the equator of the cell copyright cmassengale
    33. 33. Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres . copyright cmassengale
    34. 34. Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale
    35. 35. Meiosis II <ul><li>Only one homolog of each chromosome is present in the cell . </li></ul>Gene X copyright cmassengale Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Sister chromatids carry identical genetic information .
    36. 36. Meiosis II: Reducing Chromosome Number Prophase II Metaphase II Anaphase II Telophase II 4 Genetically Different haploid cells copyright cmassengale
    37. 37. Prophase II Nuclear envelope fragments. Spindle forms. copyright cmassengale
    38. 38. Metaphase II Chromosomes align along equator of cell. copyright cmassengale
    39. 39. Anaphase II Sister chromatids separate and move to opposite poles . Equator Pole copyright cmassengale
    40. 40. Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. copyright cmassengale
    41. 41. 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
    42. 42. Meiosis Animation copyright cmassengale
    43. 43. Gametogenesis Oogenesis or Spermatogenesis copyright cmassengale
    44. 44. Spermatogenesis <ul><li>Occurs in the testes </li></ul><ul><li>Two divisions produce 4 spermatids </li></ul><ul><li>Spermatids mature into sperm </li></ul><ul><li>Men produce about 250,000,000 sperm per day </li></ul>copyright cmassengale
    45. 45. Spermatogenesis in the Testes Spermatid copyright cmassengale
    46. 46. Spermatogenesis copyright cmassengale
    47. 47. Oogenesis <ul><li>Occurs in the ovaries </li></ul><ul><li>Two divisions produce 3 polar bodies that die and 1 egg </li></ul><ul><li>Polar bodies die because of unequal division of cytoplasm </li></ul><ul><li>Immature egg called oocyte </li></ul><ul><li>Starting at puberty, one oocyte matures into an ovum (egg) every 28 days </li></ul>copyright cmassengale
    48. 48. Oogenesis in the Ovaries copyright cmassengale
    49. 49. Oogenesis copyright cmassengale Oogonium (diploid) Mitosis Primary oocyte (diploid) Meiosis I Secondary oocyte (haploid) Meiosis II (if fertilization occurs) First polar body may divide (haploid) Polar bodies die Ovum (egg) Second polar body (haploid) a A X X a X A X a X a X Mature egg A X A X
    50. 50. Comparing Mitosis and Meiosis copyright cmassengale
    51. 51. Comparison of Divisions copyright cmassengale Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction
    52. 52. Female gametes <ul><li>Female gametes ( ova or eggs in animals, ovules in plants) </li></ul><ul><li>Fairly small numbers. </li></ul><ul><li>Human females for example release about 500 ova in a lifetime. </li></ul><ul><li>Larger </li></ul><ul><li>Stationary </li></ul><ul><li>They often contain food reserves (lipids, proteins, carbohydrates) to nourish the embryo after fertilisation </li></ul>
    53. 53. Male gametes <ul><li>Male gametes, very large numbers </li></ul><ul><li>100 million sperm per ejaculation </li></ul><ul><li>smaller </li></ul><ul><li>Motile (if they can propel themselves, mobile if they can be easily moved) </li></ul>
    54. 54. Fertilisation
    55. 55. Fertilisation