1 / 45

Understanding Chromosomes, Mitosis, and Meiosis: A Guide to Genetic Information and Cell Reproduction

This guide provides an overview of chromosomes and their role in holding genetic information, as well as the processes of mitosis and meiosis in cell reproduction. Learn about the similarities and differences between these processes and their significance in genetic inheritance.

nancyflores
Download Presentation

Understanding Chromosomes, Mitosis, and Meiosis: A Guide to Genetic Information and Cell Reproduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chromosomes Where Are the Genes Found?

  2. What Cellular Structure Holds the Genetic Information? • Chromosomes • Contain the genetic material: DNA, RNA • Chromatin • Is the chromosomal material in its decondensed, threadlike state.

  3. Mitosis • Form of asexual reproduction. • Occurs when organism grows or replaces damaged cells. • Prior to mitosis, cell undergoes replication. • Process in which chromatin is copied. • Produces diploid cells.

  4. Prophase • Start of mitosis • Chromatin condenses into rod-like chromosomes • Each chromosome consists of sister chromatids, connected at the centromere • Nuclear membrane disappears

  5. Metaphase • Chromosomes align themselves in flat plane at cell equator.

  6. Anaphase • Centromeres split. • Sister chromatids-now chromosomes- are pulled to opposite poles of the cell.

  7. Telophase • Chromosomes unravel, returning the chromatin to its non-dividing threadlike state. • Nuclear membrane assembles.

  8. Cytokinesis • Division of the cytoplasm. • Begins during anaphase and telophase.

  9. Cytokinesis • Differs in animals and plant cells. • Plant cells form a cell plate. • membranous vesicles congregate at center of cell. • Vesicles contain cell wall material.

  10. Cytokinesis • Animal cells form a cleavage furrow. • Forms around the periphery of the dividing cell. • Furrow becomes deeper and deeper until membrane pinches off forming two cells.

  11. Chromosomes Come in Matched Pairs • Homologous pairs: chromosomes that are closely matched in size and shape • Determine the same traits • Sex chromosomes: Those that determine the gender of the organism.

  12. Chromosomal Theory of Inheritance • The two members of each pair of a homologous pair of chromosomes carry alleles for the same genes and, therefore, affect the same traits. • Proposed in 1903.

  13. Mapping genes • Locus: location of a gene on a chromosome. • Currently trying to map all human genes to the appropriate chromosome. • Example: gene responsible for sickle cell anemia is located on chromosome 11.

  14. Sexual reproduction • Type of reproduction in which genetic information from female combines with male. • Requires fertilization • Fusion of gametes (egg and sperm) • These cells need to have half the amount of genetic information.

  15. Meiosis • Produces haploid cells (gametes-eggs and sperm) • Posses only one member of each pair of homologous chromosomes • Chromosomes replicate before meiosis. • Requires two rounds of division.

  16. Prophase I • Chromatin condenses into compact chromosomes. • Nuclear envelope disappears. • Synapsis occurs. • Homologous pairs of chromosomes closely align allowing exchange of chromosome segments

  17. Metaphase I • Aligned pairs of replicated chromosomes move to the equator of the dividing cell.

  18. Anaphase I • Members of homologous pairs of chromosomes separate from each other • They move to opposite poles of the cell. • Chromosomes experience independent assortment.

  19. Telophase I • Chromosomes cluster at opposite poles of cell and begin to decondense • Nuclear envelope may reform. • Cytokinesis occurs • Interkinesis: phase between meiosis I and and II. • Daughter cells now haploid.

  20. Prophase II • Partially unraveled chromosomes condense again.

  21. Metaphase II • Chromosomes move to cell equator. • No longer homologous pairs, so chromosomes line up singly in middle of cell.

  22. Anaphase II • Centromeres divide and chromosomes separate. • Move to opposite poles of the cell.

  23. Telophase II • Clustered chromosomes at cell pole begin to decondense. • Nuclear membrane develops. • Cytokinesis occurs. • Produces four non-identical haploid cells.

  24. Mitosis vs. Meiosis

  25. Cell Cycle • Repetitive sequence of events that characterizes life of cell. • Consists of two main phases: • Interphase • Period that cells are in when not dividing. • 90% of cell cycle • M phase • Includes mitosis and cytokinesis

  26. Cell Cycle

  27. Cell Cycle • Interphase has three subphases • G1 (first gap) • Cell makes copies of organelles and grows larger • S (synthesis) • Genetic material is copied • End of this phase, cells chromosomes are doubled • Copies are attached; thus total number of chromosomes remains the same • G2 (second gap) • Cell prepares upcoming M phase

  28. Regulation of Cell Cycle • Cell cycle must be regulated or can result in cancer • Uncontrolled cell growth • Metastasize: cell breaks free from original cancerous mass and resides in new area in the body

  29. Regulation of Cell Cycle • Two checkpoints • First between G1 and S • Second between G2 and M • To pass checkpoints, cell must possess appropriate amount of protein in cytoplasm. • These proteins activate other proteins necessary for production of genetic material and mitosis

  30. Regulation of Cell Cycle • To pass checkpoints, cell must possess appropriate amount of regulating protein in cytoplasm. • When regulator concentration is high, cell cycle progresses. • When low, cell cycle is suspended at that stage. • External and internal regulatory agents also influence passage through checkpoints.

  31. Why So Some Genetic Traits Tend to Travel Together? • Chromosomes contain genes • Chromosomes follow law of independent assortment, not genes • If two genes are on the same chromosome, • the two genes are inherited together or are said to be linked or in linkage groups

  32. Why So Some Genetic Traits Tend to Travel Together? • Example: sex linkage • Sex chromosomes • Contain other genes aside from those to determine gender. • Example: eye color and gender in fruit flies

  33. Chromosomes Can Exchange Segments During Meiosis • Crossing over • Exchange of genetic material between chromatids of homologous chromosomes. • Occurs at the chiasmata.

  34. Chromosomes Can Exchange Segments During Meiosis • Crossing over • Important mechanism for creating new combinations of genes. • Disrupts linkage groups.

  35. What Is the Chemical Nature of the Gene? • 1860s • Frederich Meisner studied fundamental constituents of life • Discovered unknown substance contains carbon, nitrogen, oxygen, and phosphorus. • Found it came from nucleus of cell. • Named it nucelin • His students renamed substance nucleic acid after finding it was acidic.

  36. What Is the Chemical Nature of the Gene? • 1881 • Discovered nucleic acids were contained in chromatin. • Question: Was the genetic material made of proteins or nucleic acids?

  37. DNA is the Genetic Material • 1928 • Fred Griffiths, medical officer for British Ministry of Health • Studied the bacteria pneumoncoccus • Two kinds • Smooth: Virulent form that appears smooth and shiny when grown on agar plate • Rough: harmless form that appears rough when grown on agar plate. • Experimented by injecting the two types in mice.

  38. DNA is the Genetic Material

  39. DNA is the Genetic Material • Griffiths identified the material as the transforming principle • Avery, MacLeod and McCartney • Study transforming principle for 20 years. • They determined that the transforming agent was DNA.

  40. DNA is the Genetic Material • Alfred Hershey and Martha Chase • Studied viruses that infect bacteria • Viruses are called bacteriophages

  41. DNA is the Genetic Material • Viruses are made of • Protein coat and nucleic acid • Viruses mix their genes with host genes • hijack cell machinery and use it to produces new viruses • Usually kills host cell

  42. DNA is the Genetic Material • Hershey and Chase labeled protein and DNA differently with isotopes • Variants of elements that share same chemical properties but differ in number of neutrons • Label DNA with 32P and protein with 35S

  43. DNA is the Genetic Material

More Related