Practical 3 07

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Practical 3 07

  1. 1. Practical 3 Meiosis Gametogenesis
  2. 2. Chromosomal sex determination <ul><li>Drosophila type </li></ul><ul><li>Male – XY </li></ul><ul><li>Female - XX </li></ul>
  3. 3. Sexual reproduction Life cycle: haploid phase (gametes) diploid phase (somatic cells) 2n 2n meiosis meiosis n n Gametes (haploid) sperm oocyte fertilization 2n n + n = 2n zygote ♂ ♀
  4. 4. Recommended website <ul><li>http:// genetics.gsk.com/chromosomes.htm#chromo </li></ul>
  5. 5. Written test <ul><li>8 minutes </li></ul><ul><li>Don't forget to put down your name, your group and the test version. </li></ul><ul><li>In multiple choice questions more than 1 statement could be correct. </li></ul><ul><li>Don't write anything on the question sheet! </li></ul>
  6. 6. Meiotic division 2n 1 st meiotic division 2 nd meiotic division n n n n n n
  7. 7. First meiotic division <ul><li>Heterotypic or reduction </li></ul><ul><li>Prophase </li></ul><ul><ul><li>Leptotene </li></ul></ul><ul><ul><li>Zygotene </li></ul></ul><ul><ul><li>Pachytene </li></ul></ul><ul><ul><li>Diplotene </li></ul></ul><ul><ul><li>Diakinesis </li></ul></ul><ul><li>Metaphase </li></ul><ul><li>Anaphase </li></ul><ul><li>Telophase </li></ul>
  8. 8. Leptotene <ul><li>Beginning of prophase </li></ul><ul><li>Chromosomes can't be distinguished. </li></ul><ul><li>Condensation of chromosomes begins. </li></ul>
  9. 9. Zygotene <ul><li>Attachment of homologous chromosomes – the chromosomes begin to synapse. </li></ul><ul><li>Assemblage of chromosomes is enabled by synaptonemal complex . </li></ul>
  10. 10. Pachytene <ul><li>Bivalents or tetrades are present. </li></ul><ul><ul><li>1 bivalent = 2 chromosomes </li></ul></ul><ul><ul><li>1 tetrade = 4 chromatids </li></ul></ul><ul><ul><li>bivalent = tetrade </li></ul></ul><ul><li>Crossing-over between homologous chromosomes is possible. </li></ul>
  11. 11. Crossing-over <ul><li>Reciprocal exchange of chromatid segments between chromosomal homologues </li></ul>
  12. 12. Importance of the crossing-over <ul><li>New combinations of alleles of genes that are located on the same chromosome. </li></ul><ul><li>New allele combinations lead to higher variability of the offspring (important in evolution). </li></ul><ul><li>This increases the potential for genetic variability between members of the same species . </li></ul>
  13. 13. Chromosomes X and Y <ul><li>are attached in pseudoautosomal regions (PAR) during the 1 st meiotic prophase </li></ul>X Y SRY – sex determining region – is located on chromosome Y in the neighborhood of PAR. X Y
  14. 14. Task A : <ul><li>A n infertile man with azoospermia had been examined i n cytogenetic lab. He has no other striking phenotypic features. </li></ul><ul><li>The cytogenetic analysis revealed abnormal finding because his cells contained two X chromosomes while chromosome Y is missing. </li></ul><ul><li>Explain this surprising result. </li></ul>
  15. 15. Crossing-over in PAR <ul><li>Nonreciprocal crossing-over can result in translocation of the SRY gene from the chromosome Y to chromosome X </li></ul>
  16. 16. Task A – result male female Normal combination of gonosomes X;Y translocation XX XY „ XX-male“ „ XY-female“
  17. 17. Hermaphroditism – possible consequence of sex chromosome abnormalities
  18. 18. Prophase of the 1 st meiotic division next periods
  19. 19. Pachytene
  20. 20. Diplotene <ul><li>Condensation of chromosomes continues </li></ul><ul><li>Homologous chromosomes are divided </li></ul><ul><li>Disassembling of synaptonemal complex </li></ul><ul><li>At the end of diplotene homologues are connected only in crossover sites. These sites are called chiasmata (singular: chiasma). </li></ul>
  21. 21. Diakinesis <ul><li>Final period of the 1st meiotic prophase. </li></ul><ul><li>Chiasmata are transferred to terminal chromosomal regions. </li></ul><ul><li>Under specific staining chromosomes could be well distinguished under the microscope. </li></ul><ul><li>Nuclear membrane disappears. </li></ul>
  22. 22. Terminal phases of meiotic division prophase metaphase + anaphase 2 nd meiotic division (homeotypic) 1 st meiotic division (heterotypic) Separation of double-chromatid homologous chromosomes
  23. 23. Metaphase I Metaphase I
  24. 24. Anaphase I X Anaphase II
  25. 26. Gametogenesis <ul><li>Spermatogenesis – sperm development </li></ul><ul><li>Oogenesis – oocyte development </li></ul>
  26. 27. Spermatogenesis n n 1st meiotic division 2nd meiotic division n n primary spermatocyte secondary spermatocyte sperm n n 2n
  27. 28. Oogenesis n n 1st meiotic division 2nd meiotic division n n primary oocyte secondary oocyte mature oocyte n n 2n polar bodies polar body
  28. 29. A schedule of oocyte development Prophase I fetus childhood – dictyotene mature ovary fertilization
  29. 30. Spermatogenesis X Oogenesis
  30. 31. Task B : Risk of chromosomal nondisjunction defects <ul><li>Compare possible risk of chromosomal abnormalities for two couples that visited the genetic counselling clinic: </li></ul><ul><ul><li>Couple 1: female (21 years), male (38 years) </li></ul></ul><ul><ul><li>Couple 2: female (36 years), male (32 years) </li></ul></ul><ul><li>Which family has higher risk of numerical chromosomal aberrations? </li></ul>
  31. 32. Task B – result <ul><li>Oogenesis lasts much longer than spermatogenesis – risk of chromosomal nondisjunction defects is age-related. </li></ul><ul><li>The second couple has higher risk due to 36 years old female. </li></ul><ul><li>In pregnant females older than 35 years prenatal examination of the fetus is recommended. </li></ul>35 years … risk 1/365 Age-related risk of the Down syndrome child Mother´s age
  32. 33. Practical tasks
  33. 34. Task 1 : Observation of meiosis in the grasshopper testis <ul><li>The slide was prepared from the testis of the grasshopper. After removing from the individual the tissue was fixed with methanol + glacial acetic acid (3 : 1) and stained with the Giemsa-Romanowski solution. After dehydration the tissue was mounted in the Canada balsam. </li></ul><ul><li>Find the spermatocytes on the slide using 10x objective lens. </li></ul><ul><li>Change the objective magnification into 40 or 45x and observe different phases of meiosis. For their determination use adjacent photos. </li></ul>
  34. 35. Task 2 : Disjunction of the sex chromosomes during meiosis <ul><li>Redraw the scheme of disjunction of the sex chromosomes during meiosis of the male to your materials and fill it. </li></ul><ul><li>In the first scheme (A) distinguish the chromosomes according to their shape and number of chromatids. </li></ul><ul><li>In the second scheme (B) designate the chromosomes using letters X or Y no matter of the number of chromatids. </li></ul>A B XY
  35. 36. Task 3 : Changes of nuclear DNA concentration during the cell cycle <ul><li>Contrast the two types of cell division (mitosis X meiosis) by completing the following graphs below. </li></ul><ul><li>Redraw the picture to your materials and fill curves demonstrating changes in the DNA content per one cell: </li></ul><ul><ul><li>during the cell cycle followed with mitosis </li></ul></ul><ul><ul><li>during the cell cycle followed with meiosis. </li></ul></ul><ul><li>(Value „C“ on y-axis represents DNA content per one cell in G1 phase.) </li></ul>
  36. 37. Task 3 : Changes of nuclear DNA concentration during the cell cycle G 1 G 2 S M G 1 C 2C G 1 G 2 S M 1 M 2 G 1 Cell cycle + mitosis Cell cycle + meiosis Nuclear DNA content
  37. 38. Results
  38. 39. Task 3: Observation of meiosis in the grasshopper testis
  39. 40. Task 4: Disjunction of the sex chromosomes during meiosis Scheme A Scheme B XY X Y X X Y Y
  40. 41. Task 5: Changes of nuclear DNA concentration during the cell cycle G 1 G 2 S M G 1 C 2C G 1 G 2 S M 1 M 2 G 1 Cell cycle + mitosis Cell cycle + meiosis Nuclear DNA
  41. 42. Assisted reproduction <ul><li>A group of methods that allows reproduction of infertile couple that can't be therapeuted by common medical treatment (e.g. using drugs of by psychological intervention) </li></ul><ul><li>The assisted reproduction could be also used for prevention of genetic defects in families with normal fertility but with increased risk of genetically conditioned disorder for the offspring. </li></ul>
  42. 43. Assisted reproduction methods <ul><li>Intrauterine artificial insemination </li></ul><ul><ul><li>application of sperm to the uterus of the female. </li></ul></ul><ul><li>In vitro fertilization and embryo transfer </li></ul><ul><ul><li>fertilization is performed outside the organism of the mother </li></ul></ul>
  43. 44. Artificial insemination <ul><li>homologous – the female is fertilized with sperm of her husband; </li></ul><ul><li>sperm of anonymous donor are applied – the donor and the couple remain unknown to each other </li></ul>
  44. 45. In vitro fertilization <ul><li>Application of gonadotropins (= fertility drugs) induce maturation of numerous oocytes. </li></ul><ul><li>The oocytes are removed from ovaries by biopsy. In a special dish they are mixed with sperms of the husband. </li></ul><ul><li>After short term cultivation in medium with nutrients 3 embryos are transferred to the female's uterus. </li></ul>
  45. 46. ICSI (intracytoplasmatic sperm injection)
  46. 47. ICSI protocol
  47. 48. Preimplantation diagnostics <ul><li>Genetic or other examinations of oocytes or embryo before transfer to the mother's </li></ul><ul><li>We use </li></ul><ul><ul><li>Polar body </li></ul></ul><ul><ul><li>1 – 2 cells from 8-cell embryo </li></ul></ul><ul><ul><li>More cells from blastocyst </li></ul></ul>
  48. 49. Presentation Ethical issues of assisted reproduction
  49. 50. Next seminar <ul><li>In vitro cell cultivation </li></ul><ul><li>Recommended websites: </li></ul><ul><ul><li>http://www.research.umbc.edu/~jwolf/method5.htm </li></ul></ul><ul><ul><li>http://homepages.gac.edu/~cellab/chpts/chpt12/intro12.html </li></ul></ul><ul><li>Be careful when handling cell cultures! </li></ul><ul><li>Test: previous topics (only seminars) </li></ul>
  50. 51. See you next week!

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