SBB 1054 Genetics Lecture Notes
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This document contains information about an genetics course, including important dates for tests and assignments, as well as content on mitosis, meiosis, crossing over, and the Holliday model. It provides an overview of mitosis and meiosis, explaining that mitosis produces two genetically identical daughter cells while meiosis results in four genetically unique haploid cells. It also describes the process of crossing over during prophase I of meiosis, including the role of the Holliday model in facilitating genetic recombination between homologous chromosomes.
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SBB 1054 Genetics Lecture Notes
- 1. SBB 1054 Genetics Prepared by Pratheep Sandrasaigaran Lecturer at Manipal International University 1
- 2. IMPORTANT DATES..! 1. Test 1- Week 6 (20th – 24th MAC 2017) 2. Test 2- Week 11 ( 24th – 28th APR 2017) 3. Assignment 2- 3rd May 2017 (Week 12) 4. Study Break- Week 15 (22nd – 26th MAY 2017) 5. Exam- Week 16 & 17 (29th MAY – 9th JUN 2017) Prepared by Pratheep Sandrasaigaran Figure taken from Internet 2
- 3. Prepared by Pratheep Sandrasaigaran Lecturer at Manipal International University 3.0 Crossing over 3
- 4. Prepared by Pratheep Sandrasaigaran • Overview of Mitosis and Meiosis • Crossing over • Holliday model By the end of this chapter you should be able to: 4 Diagram adopted from Internet
- 5. 3.1 Overview of Mitosis and Meiosis Prepared by Pratheep Sandrasaigaran 5
- 6. Mitosis • Two genetically identical diploid (2n) daughter cells are produced. • Mitosis : 2n 2n • Distinct phases: - Prophase - Metaphase - Anaphase - Telophase - Cytokinesis* Prepared by Pratheep Sandrasaigaran 6 2n 2n 2n
- 7. Prepared by Pratheep Sandrasaigaran 7 Cell cycle 1. Interphase 2. Mitosis Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 8. Cell cycle & Mitosis Prepared by Pratheep Sandrasaigaran 8 Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 9. Mitosis Prepared by Pratheep Sandrasaigaran 9 Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 10. 10 Mitosis Prepared by Pratheep Sandrasaigaran
- 11. Meiosis Prepared by Pratheep Sandrasaigaran 11 Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 12. Prepared by Pratheep Sandrasaigaran 12 Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 13. Comparison of mitosis & meiosis Prepared by Pratheep Sandrasaigaran 13 Diagram adopted from Genetics for Genetics- Conceptual Approach, Benjamin A. Pierce
- 14. TEST YOUR KNOWLEDGE 1 Prepared by Pratheep Sandrasaigaran 14
- 15. Prepared by Pratheep Sandrasaigaran Define the following: • Gene • Allele • Locus • Chromatin • Chromosome • Sister chromatids • Centromere • Centrosome 15
- 16. 3.2 Crossing over Prepared by Pratheep Sandrasaigaran 16
- 17. 17 Prepared by Pratheep Sandrasaigaran Crossing over • The process of crossing over (recombination) between homologs depends on the breakage and rejoining of the DNA strands. • This results in the exchange of genetic information between DNA molecules to increase genetic diversity.
- 18. 18 Prepared by Pratheep Sandrasaigaran Crossing over • The genetic exchange may happen between any two homologous double stranded DNA molecules • Virus chromosomes • Bacterial chromosomes • Eukaryotic homologs during meiosis
- 19. 19 Prepared by Pratheep Sandrasaigaran Crossing over Diagram adopted from Internet
- 20. 20 Prepared by Pratheep Sandrasaigaran Why do chromosomes undergo crossing over? • Include roles in specialized DNA repair systems. • Specialized activities in DNA replication • Regulation of expression of certain genes. • Facilitation of proper chromosome segregation during eukaryotic cell division. • Maintenance of genetic diversity • Implementation of programmed genetic rearrangements during embryonic development.
- 21. 21 Prepared by Pratheep Sandrasaigaran Recombination ABCDEFGhijklmnoPQRSTUVWXYZ abcdefgHIJKLMNOpqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz
- 22. 22 Prepared by Pratheep Sandrasaigaran • Figure: The homologous chromosomes of a grasshopper are shown during prophase I of meiosis. • Many points of joining (chiasmata) are evident between the two homologous pairs of chromatids. • These chiasmata are the physical manifestation of prior homologous recombination (crossing over) events. Recombination in Grasshopper Diagram adopted from Internet
- 23. 3.3 Crossing over- Holliday model Prepared by Pratheep Sandrasaigaran 23
- 24. 24 Prepared by Pratheep Sandrasaigaran Holliday model • By Robin Holliday and Harold L. K. Whitehouse in 1964 • How to defines Holliday model? I. Start with the formation of heteroduplex DNA; the creation of a cross bridge II. Cross bridge migrates along the two heteroduplex strands (branch migration) III. Resolution or splicing, of the intermediate structure to yield different types of recombinant molecules.*
- 25. 25 Prepared by Pratheep Sandrasaigaran
- 26. 26 Prepared by Pratheep Sandrasaigaran Holliday model • Two homologous double helices (duplexes) are shown. • Each pair represents a chromatid and the two pairs represent two non-sister chromatids. • The helices are aligned so that the bottom strand of the first helix has the same polarity as the top strand of the second helix.
- 27. 27 Prepared by Pratheep Sandrasaigaran Holliday model • Two parallel or two antiparallel strands are cut by endonuclease. • The free ends become associated with the complementary strands in the homologous double helix. 3’ 3’ 3’ 3’ 5’ 5’ 5’ 5’
- 28. 28 Prepared by Pratheep Sandrasaigaran Holliday model • Ligation creates hybrid duplexes called heteroduplex DNA molecules, held together by a cross-bridge structure. • The position of this cross bridge can then move down the chromosome by a process referred to as branch migration. • This occurs as a result of a zipper-like action as hydrogen bonds are broken and then re-formed between complementary bases of each duplex.
- 29. 29 Prepared by Pratheep Sandrasaigaran
- 30. 30 Prepared by Pratheep Sandrasaigaran Two possible outcomes.. How? A Better View Diagram adopted from Internet
- 31. 31 Prepared by Pratheep Sandrasaigaran Diagram adopted from: Concepts of Genetics, Klug, Cummings, Spencer, Palladino, 2012 III. Resolution of the Holliday structure.
- 32. 32 Prepared by Pratheep Sandrasaigaran III. Resolution of the Holliday structure. Isomerization Diagram adopted from: Concepts of Genetics, Klug, Cummings, Spencer, Palladino, 2012
- 33. 33 Prepared by Pratheep Sandrasaigaran III. Resolution of the Holliday structure. Endonuclease nicking Diagram adopted from: Concepts of Genetics, Klug, Cummings, Spencer, Palladino, 2012 nick nick 1 2
- 34. 34 Prepared by Pratheep Sandrasaigaran Resolution Horizontal Vertical No exchange Exchange Non-recombinant product/ patch Recombinant product/ splice III. Resolution of the Holliday structure. Diagram adopted from Internet
- 35. 35 Prepared by Pratheep Sandrasaigaran TEST YOUR KNOWLEDGE 2 • Build a plastisin clay model for holliday model in a group Diagram adopted from Internet