biologia6

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biologia6

  1. 1. Variability causes in Meiosis 1. Crossing over 3.Separation of sister Chromatides during ANAPHASE II 2.Homologous Chromosomes Separation during ANAPHASE I
  2. 2. **
  3. 3. p q Arm Arm The Centromere divides each Chromatid in two arms than can be equal or different. METAPHASIC CHROMOSOME STRUCTURE
  4. 4. Metacentric p q Near the middle off Centre near one end at the end Because the Centromere is not exactly in the centre of a Chromosome, each chromosome has a sort arm and a long arm. The short arm is designated with the letter p (for the French petite) While the long arm is designated with q.
  5. 5. Metacentric p q Near the middle off Centre near one end at the end In Human Beings do not exist Telocentric Chromosomes
  6. 6. Metacentric To classify the Human Chromosomes following the Centromeric location we have to use The Chromosomic Indexes:
  7. 7. They are used to classify human chromosomes.
  8. 8. They are used to classify human chromosomes. p q
  9. 9. p q
  10. 10. A photography of the Metaphasic Chromosomes. Without order. Ordered Chromosomes following Cytogenetic Criteria.
  11. 11. G BANDS
  12. 12. Types of banding G-Banding is obtained with Giemsa stain following digestion of chromosomes with trypsin. It yields a series of light and dark bands - the dark regions tend to be heterochromatic, (DNA more condensed) and AT rich. The light regions tend to be euchromatic, (Less condensed)and GC rich. This method will normally produce 300-400 bands in a normal, human genome
  13. 13. PAINTING CHROMOSOMES USING SPECIFIC SOFTWARE
  14. 14. Phytohemagglutinin In medicine this protein is useful and is used as a mitogen to trigger lymphocytes cell division
  15. 15. BLOOD OR BONE NARROW
  16. 16. Colchicine to stop Mitosis
  17. 17. Phytohemagglutinin In medicine this protein is useful and is used as a mitogen to trigger lymphocytes cell division
  18. 18. Colchicine is got from Colchicum autumnale. Colchicine stops Mitosis in Metaphase.
  19. 19. To classify Chromosomes we use three main criteria: ** ** ** . For example, .
  20. 20. Phytohemagglutinin In medicine this protein is useful and is used as a mitogen to trigger lymphocytes cell division
  21. 21. Amniocentesis Chorionic villi Sampling
  22. 22. Amniocentesis Chorionic villi Sampling From fifteenth to seventeenth week of pregnancy From eighth to twelfth week of pregnancy Risk of Spontaneous abortion 0.3% Risk of Spontaneous abortion 0.8 %
  23. 23. Risk of Spontaneous abortion 0.8 %
  24. 24. Risk of Spontaneous abortion 0.8 %
  25. 25. From fifteenth to seventeenth week of pregnancy Risk of Spontaneous abortion 0.3%
  26. 26. In human Beings , the Euploid condition is two sets of 23 Chromosomes each; 46 Chromosomes. The somatic cells are Diploid
  27. 27. Organisms with three or more sets of Chromosomes are called POLYPLOID. A Diploid organism is referred to as 2n, a Triploid organism as 3n, a Tetraploid organism as 4n, and so forth. Haploid individuals or cells are referred as n.(only a set of chromosomes). In Human beings Poliploids individuals are extremely rare and only these individuals have been got in abortions. Observe the following figures because they are cases of Triploid Human beings.
  28. 28. At A the Strawberry plant is exposed to a chemical called Colchicine. At B due tho the effect of the drug, total no disjunction produced Diploid gametes(2n). As a result, at C two Diploid gametes fuse at fertilization . Finally at D a new polyploid plant is formed
  29. 29. Observe......................... Julia Sáenz Hurtado Servicio de Inmunología. Sección Genética Hospital Infanta Cristina
  30. 30. Julia Sáenz Hurtado Servicio de Inmunología. Sección Genética Hospital Infanta Cristina Observe again
  31. 31. The second way that chromosomes number varies is a phenomenon called . This refers to an alteration in the number of particular Chromosomes, so that the total number of chromosomes is not an exact multiple of a set. In human beings Aneuploid individuals have a chromosome number that is not an exact multiple of the haploid number of 23. The normal condition is the DISOMY (Two chromosomes in a pair) but the abnormal condition may be:
  32. 32. Normal Condition Embryos missing a chromosome usually die; hence,monosomy of an autosome is extremely rare in living persons. About 97 % of embryos lacking a sex chromosome also die, but some survive and develop characteristics of TURNER SYNDROME or XO.
  33. 33. 45,X
  34. 34. TURNER SYNDROME
  35. 35. TURNER SYNDROME LINDA HUNT
  36. 36. Meiosis Review 1. REDUCTION OF NUMBER OF CHROMOSOMES BY HALF 2.Meiosis only occurs in germ cells.
  37. 37. Variability causes in Meiosis 1. Crossing over 3.Separation of sister Chromatides during ANAPHASE II 2.Homologous Chromosomes Separation during ANAPHASE I
  38. 38. 1. Crossing over Exchange of Genetic Material between Homologous Chromosomes
  39. 39. 2.Homologous Chromosomes Separation during ANAPHASE I Either or A B A B
  40. 40. A1 A2 A1 A2 A3 A4 A3 A4 ANAPHASE II 3.Separation of sister Chromatides during ANAPHASE II
  41. 41. p q Sister Chromatids Each one is a Molecule of DNA Arm Arm The Centromere divides each Chromatid in two arms than can be equal or different. METAPHASIC CHROMOSOME STRUCTURE
  42. 42. Based on Centromere location, each chromosome is classified as: Metacentric p q Comparison of centromeric locations Near the middle off Centre near one end at the end
  43. 43. To classify Chromosomes we use three main criteria: ** ** ** . For example, .
  44. 44. If three chromosomes are present instead of the usual pair. The common cause of Trisomy is nondisjunction (no Homologous separation) during the Meiosis(special division that suffer the gametes).The result is a gamete (Ovum or Sperm) with 24 Chromosomes instead of 23 Chromosomes and, after the fertilization the result is a Zygote with 47 chromosomes. IMPORTANT: Autosomal Trisomies occur with increasing frequency as maternal age increases.
  45. 45. Nondisjunction DURING MEIOSIS
  46. 46. Translocation Down syndrome occurs when two chromosomes, one of which must be a 21, join together at their ends. Instead of having three independent, separate number 21 chromosomes, a person with translocation Down syndrome has two independent 21 chromosomes and a 21 chromosome that is attached to another chromosome. Observe as examples the Idiograms with a Tranlocation 21:21 and a Translocation 21:14.
  47. 47. Simian Crease
  48. 48. Simian Crease

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