Meiosis & Sexual Reproduction
Sexual Reproduction►2  parents► Exchange of DNA► Offspring genetically different from parents► Involves specialized sex ce...
Sexual Reproduction in Simple         Organisms            ► Conjugation   –               Cytoplasm bridge forms        ...
Sexual Reproduction in Animals► Each   parent produces a GAMETE   Female gamete – egg   Male gamete - sperm► The   two g...
Somatic cells vs. Gametes► Somatic   cells are body cells     2 set of chromosomes     Humans have 46 chromosomes or 23 ...
How are gametes produced?   ► Eggs  & sperm need to be made and     joined…   ► Do we make egg & sperm by mitosis? No!What...
diploid = 2 copies 2n   Human female karyotype               46 chromosomes               23 pairs                        ...
diploid = 2 copies 2n   Human male karyotype              46 chromosomes              23 pairs                            ...
Paired chromosomes► Homologous  chromosomes   both chromosomes of a pair carry “matching”    genes    ►control           ...
How do we make sperm & eggs? ► Must   reduce 46 chromosomes → 23    must half the number of chromosomes    haploid      ...
Meiosis makes sperm & eggs► 46   chromosomes to 23 chromosomes   half the number of chromosomes          46              ...
Meiosis► Specialcell division in sexually reproducing  organisms► Makes gametes   Sperm & egg► Reduction   division     ...
Interphase     ► DNA   replicates     ► Cell prepares for       division
Prophase I     ►   Homologous chromosomes         pair up and form a tetrad          This is called synapsis     ►   Cros...
Metaphase I      ► Tetrads  line up at the        equator.      ► Centromeres attach        chromosomes to the        spin...
Anaphase I     ► Homologous      chromosomes separate      and move to the poles        Called disjunctions        Siste...
Telophase I      ►   Cytoplasm divides, forming          two new daughter cells           Cells are haploid
Cytokinesis I► Occurs   simultaneously with telophase I   Forms 2 daughter cells► Plantcells – cell plate► Animal cells –...
Prophase II      ► Spindle  forms      ► Sister chromatids        move toward the        equator
Metaphase II      ► Sister chromatids line        up at the equator         Similar to mitosis      ► Spindle fibers atta...
Anaphase II      ► Sisterchromatids        separate and move to        opposite poles
Telophase II      ► Nuclei form at poles        and cytokinesis occurs      ► After completion of        cytokinesis there...
double            Meiosis 1 overview               stranded   ► 1st                                  Divide 1           di...
Bye Bye 2             Meiosis 2 overview                                         telophase 2         telophase 1      Line...
► Meiosis   Square Dance                  Let’s Dance!!
Sexual reproduction lifecycle                                             2 copies                                       ...
Putting it all together…meiosis → fertilization → mitosis + development            gametes46             23               ...
The value of meiosis 1  ► Consistency   over time       meiosis keeps chromosome number same        from generation to ge...
The value of meiosis 2                We’re                                      mixing things                            ...
Fertilization► Joining of the sperm & egg► Internal Fertilization     Gametes fuse inside the body of a female     Occur...
Fertilization► Parthenogenesis   Development of an unfertilized egg into an adult    animal   E.g. rotifers, some insect...
Independent Assortment► Chromosomes   are separated and combined independently of each other during meiosis   E.g. all yo...
Independent Assortment► Independent            assortment produces many different gametes   In humans, n=23 so over 8    ...
Crossing Over► Occurs  in prophase I, during synapsis► Homologous chromosomes twist and exchange  pieces of genetic materi...
The Key Difference Between Mitosis and Meiosis isthe Way Chromosomes Uniquely Pair and Align in                    Meiosis...
Problems in Meiosis► Sometimes    chromosomes don’t separate properly   This is called nondisjunction and result in a cel...
Problems in Meiosis
Problems in MeiosisShould the gamete with thechromosome pair be fertilizedthen the offspring will not be‘normal’.In humans...
Trisomy 21– Downs Syndrome               Can you see the extra               21st chromosome?               Is this person...
Gametogenesis► Gametes    develop within specialized organs     Female gametes – egg cells     Male gametes – sperm cell...
Gametogenesis►Gametogenesis  – the formation of gametes in the gonads  Two types:   ►Oogenesis   – formation of eggs by  ...
Spermatogenesis► Produces   4 haploid sperm
Oogenesis► Produces   1 haploid egg and 3 haploid polar bodies
Hermaphrodites► Hermaphrodites   have both testes and ovaries   E.g. earthworm, snails, and hydra
Copy of meiosis2010
Copy of meiosis2010
Copy of meiosis2010
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  • Consider the greater variation with 23 pairs of chromosomes = mixing and matching
  • Consider the greater variation with 23 pairs of chromosomes = mixing and matching
  • Use 2 n to determine how many different gametes are possible In humans, n=23 so and 2 23 = 8,388,608
  • Copy of meiosis2010

    1. 1. Meiosis & Sexual Reproduction
    2. 2. Sexual Reproduction►2 parents► Exchange of DNA► Offspring genetically different from parents► Involves specialized sex cells (gametes)► Creates diversity
    3. 3. Sexual Reproduction in Simple Organisms ► Conjugation –  Cytoplasm bridge forms between 2 cells and an exchange of DNA takes place  Occurs between two cells with different mating types  Mating types are usually called plus (+) and minus (-)
    4. 4. Sexual Reproduction in Animals► Each parent produces a GAMETE  Female gamete – egg  Male gamete - sperm► The two gametes combine and produce a zygote  Called fertilization► Thezygote then divides by mitosis, grows and process begins again  Zygote has the same number of chromosomes as the parents
    5. 5. Somatic cells vs. Gametes► Somatic cells are body cells  2 set of chromosomes  Humans have 46 chromosomes or 23 pairs► Gametes are sex cells  1 set of chromosomes  Humans have 23 chromosomes
    6. 6. How are gametes produced? ► Eggs & sperm need to be made and joined… ► Do we make egg & sperm by mitosis? No!What if we did, then… 46 + 46 92 egg sperm zygote Doesn’t work!
    7. 7. diploid = 2 copies 2n Human female karyotype 46 chromosomes 23 pairs XX
    8. 8. diploid = 2 copies 2n Human male karyotype 46 chromosomes 23 pairs XY
    9. 9. Paired chromosomes► Homologous chromosomes  both chromosomes of a pair carry “matching” genes ►control same inherited characters ►homologous = same information diploid 2n eye color eye color 2n = 4 (brown?) (blue?) homologous double stranded chromosomes homologous chromosomes
    10. 10. How do we make sperm & eggs? ► Must reduce 46 chromosomes → 23  must half the number of chromosomes  haploid zygote46 23 23 meiosis egg 46 2346 23 fertilization sperm gametes
    11. 11. Meiosis makes sperm & eggs► 46 chromosomes to 23 chromosomes  half the number of chromosomes 46 23 egg meiosis 46 23diploid sperm haploid
    12. 12. Meiosis► Specialcell division in sexually reproducing organisms► Makes gametes  Sperm & egg► Reduction division  Reduce number of chromosomes  2n  1n  diploid  haploid
    13. 13. Interphase ► DNA replicates ► Cell prepares for division
    14. 14. Prophase I ► Homologous chromosomes pair up and form a tetrad  This is called synapsis ► Crossing over occurs during synapsis  Homologous chromosomes exchange segments of DNA
    15. 15. Metaphase I ► Tetrads line up at the equator. ► Centromeres attach chromosomes to the spindle fibers
    16. 16. Anaphase I ► Homologous chromosomes separate and move to the poles  Called disjunctions  Sister chromatids remain attached
    17. 17. Telophase I ► Cytoplasm divides, forming two new daughter cells  Cells are haploid
    18. 18. Cytokinesis I► Occurs simultaneously with telophase I  Forms 2 daughter cells► Plantcells – cell plate► Animal cells – cleavage furrow► There is no further replication of genetic material prior to meiosis II
    19. 19. Prophase II ► Spindle forms ► Sister chromatids move toward the equator
    20. 20. Metaphase II ► Sister chromatids line up at the equator  Similar to mitosis ► Spindle fibers attach at the centromere
    21. 21. Anaphase II ► Sisterchromatids separate and move to opposite poles
    22. 22. Telophase II ► Nuclei form at poles and cytokinesis occurs ► After completion of cytokinesis there are 4 daughter cells  Each cell is haploid (n)
    23. 23. double Meiosis 1 overview stranded ► 1st Divide 1 division of meiosis Copy DNA Line Up 14 prophase 1 metaphase 1 chromosomes telophase 1 diploid 2n  2 chromosomes  haploid gamete  1n
    24. 24. Bye Bye 2 Meiosis 2 overview telophase 2 telophase 1 Line Up 2 4► 2nd division of meiosis  looks like mitosis metaphase 2  2 chromosomes  haploid  1n gametes
    25. 25. ► Meiosis Square Dance Let’s Dance!!
    26. 26. Sexual reproduction lifecycle  2 copies  diploid  2n 1 copy  1 copy fertilization meiosis haploid  haploid 1n  1n We’re mixing things up here! A good thing?
    27. 27. Putting it all together…meiosis → fertilization → mitosis + development gametes46 23 46 23 46 46 meiosis egg 46 4646 23 46 46 4646 23 zygote fertilization mitosis & mitosis sperm development
    28. 28. The value of meiosis 1 ► Consistency over time  meiosis keeps chromosome number same from generation to generation from MomMomDad offspring from Dad
    29. 29. The value of meiosis 2 We’re mixing things up here! ► Change over time  meiosis introduces genetic variation ►gametes of offspring do not have same genes as gametes from parents ►new combinations of traitsfrom Dad variationfrom Mom offspring new gametes made by offspring
    30. 30. Fertilization► Joining of the sperm & egg► Internal Fertilization  Gametes fuse inside the body of a female  Occurs in many land animals  Offspring have a better chance of survival  Fewer offspring are produced► External Fertilization  Gametes fuse outside the body of a female  Occurs in many water animals  Many offspring produced  Fewer offspring survive
    31. 31. Fertilization► Parthenogenesis  Development of an unfertilized egg into an adult animal  E.g. rotifers, some insects such as bees, wasps,  E.g. Queen bee can produce fertilized or unfertilized eggs. ►Fertilized eggs become female workers ►Unfertilized eggs become male drones
    32. 32. Independent Assortment► Chromosomes are separated and combined independently of each other during meiosis  E.g. all your mom’s chromosomes don’t end up together in your gametes. They are randomly mixed.
    33. 33. Independent Assortment► Independent assortment produces many different gametes  In humans, n=23 so over 8 million different gametes can be produced…
    34. 34. Crossing Over► Occurs in prophase I, during synapsis► Homologous chromosomes twist and exchange pieces of genetic material► This results in even more different gametes
    35. 35. The Key Difference Between Mitosis and Meiosis isthe Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis
    36. 36. Problems in Meiosis► Sometimes chromosomes don’t separate properly  This is called nondisjunction and result in a cell with too many or too few chromosomes
    37. 37. Problems in Meiosis
    38. 38. Problems in MeiosisShould the gamete with thechromosome pair be fertilizedthen the offspring will not be‘normal’.In humans this often occurswith the 21st pair – producinga child with Downs Syndrome
    39. 39. Trisomy 21– Downs Syndrome Can you see the extra 21st chromosome? Is this person male or female? •This picture of a person’s chromosomes is called a karyotype. The chromosomes are organized from largest to smallest. •How can karyotypes be helpful in identifying diseases?
    40. 40. Gametogenesis► Gametes develop within specialized organs  Female gametes – egg cells  Male gametes – sperm cells  Female gonads – ovaries  Male gonads - testes
    41. 41. Gametogenesis►Gametogenesis – the formation of gametes in the gonads  Two types: ►Oogenesis – formation of eggs by meiosis ►Spermatogenesis – formation of sperm by meiosis
    42. 42. Spermatogenesis► Produces 4 haploid sperm
    43. 43. Oogenesis► Produces 1 haploid egg and 3 haploid polar bodies
    44. 44. Hermaphrodites► Hermaphrodites have both testes and ovaries  E.g. earthworm, snails, and hydra

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