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Chapter 5

Chapter 5. Genetics: The Continuity of Life. What is genetics?. The study of heredity —the passing on of characteristics (in the form of genes) from parents to offspring. History of Genetics. Aristotle Traits passed through the parents’ blood

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Chapter 5

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  1. Chapter 5 Genetics: The Continuity of Life

  2. What is genetics? The study of heredity—the passing on of characteristics (in the form of genes) from parents to offspring

  3. History of Genetics • Aristotle • Traits passed through the parents’ blood • “Particulate theory of reproduction” • Preformationists • Complete organism in the father’s sperm

  4. History of Genetics • Gregor Mendel • Traits caused by “factors” which parents donate to their offspring • “Father of Genetics” • Watson and Crick • Described the structure of DNA

  5. GenesandChromosomes

  6. Gene A section of DNA that codes for a particular polypeptide chain of amino acids, thereby producing a trait

  7. Characteristics of Genes • Genes are the same in type and amount in the cells of an organism. • Genes are the same in type and amount in the cells of each organism of a species.

  8. Characteristics of Genes • Genes are chemicals that can function as individual units. • Genes carry information for the formation of organic chemicals (biosynthesis).

  9. Characteristics of Genes • Genes are able to reproduce themselves. • Genes can be passed on to the next generation. • Genes are found in the cell’s nuclear material.

  10. What is a chromosome? Genes are located on chromosomes.

  11. chromosome:a strand of DNA with proteins attached histones: proteins that support and protect the DNA

  12. chromatin material: a fuzzy, tangled mass of chromosomes in a non-dividing cell

  13. chromatid:one half of a duplicated chromosome ready for cell division

  14. centromere: the point at which two chromatids are attached

  15. Chromosome Numbers • The number of chromosomes in a cell is a species characteristic.

  16. It is not the number of chromosomes that determines a species, but rather the genes on the chromosomes.

  17. Chromosome Numbers • Karyotype—a picture of the chromosomes in a cell

  18. Chromosome NumbersChromosomes come in pairs. • There are 23 pairs of chromosomes in a human cell.

  19. Chromosome NumbersChromosomes come in pairs. • Each pair is called a homologous pair of chromosomes. • Each member of a pair is called a homologue.

  20. Diploid = 2n homologous pairs of chromosomes humans = 23 pairsor 2n = 46

  21. Both homologues in a pair have genes for the same characteristics.

  22. Haploid = n one set of chromosomes In humans, n = 23.

  23. The Cell Cycle • The cell cycle has three major phases. • Interphase is the time of growth for the cell.

  24. The Cell Cycle • The cell cycle has three major phases. • Mitosis is the division of the nuclear material. • It is the process whereby the copies of the genetic material are separated into two sets.

  25. The Cell Cycle • The cell cycle has three major phases. • Cytokinesis is the division of the cytoplasm.

  26. Interphase • Major time of growth; most time spent in this phase • Time between divisions • Transcription and replication • Divided into three stages • G1, S, G2

  27. Interphase • G1 phase • Major growth spurt • Increase in size • Produce new organelles and proteins • Ends when the cell reaches maturity

  28. Interphase • S phase • DNA is replicated (and the chromosomes duplicated). • The centrosome divides.

  29. Interphase • G2 phase • Cell produces proteins and molecules needed for mitosis. • A cell that is ready to divide is called a mother cell.

  30. interphase

  31. Mitosis • Division of the nuclear material • Results in each nucleus having an identical copy of the genetic information from the mother cell

  32. Mitosis • Four phases • Prophase • Metaphase • Anaphase • Telophase

  33. Prophase • Chromosomes coil up, becoming short and thick. • DNA duplicates are called sister chromatids. • Sister chromatids are attached at the centromere.

  34. Prophase • Nuclear membrane disintegrates. • Centrosomes migrate to opposite sides of the cell and form the mitotic spindle.

  35. prophase sister chromatids

  36. Metaphase • Chromosomes are positioned at the center of the cell. • Centromeres line up on the equatorial plane.

  37. metaphase spindle

  38. Anaphase • Sister chromatids separate, forming daughter chromosomes. • Centromeres pull the daughter chromosomes along the spindle fiberstoward opposite poles of the cell.

  39. anaphase

  40. Telophase • Daughter chromosomes are at the ends of the spindle. • A new nuclear membrane forms around each set of chromosomes (daughter nuclei).

  41. telophase

  42. Cytokinesis • Division of the cytoplasmic contents (organelles, proteins, membranes, cytoskeleton) • Animal cells: contractile ring • Plant cells: cell plate

  43. cytokinesis

  44. Variations in Mitosis • Unicellular organisms • Sometimes no cytokinesis • Plants vs. animals • Cytokinesis • Centrioles

  45. Variations in Mitosis • All cells • Amount of time • Number of divisions

  46. Uses of Mitosis • In multicellular organisms, mitosis allows for growth and repair. • Many organisms carry on reproduction using mitosis. • Asexual reproduction

  47. Asexual Reproduction • Producing a new organism using only mitotic cell divisions • Examples • Fragmentation • Budding • Spores

  48. Meiosis The reduction of a cell’s chromosome number from diploid to haploid by two consecutive cell divisions

  49. Meiosis • Forms haploid cells • Haploid cells (one from each parent) can then unite to form a diploid cell called a zygote.

  50. The reason:2n + 2n = 4nNot Good!

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