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G enetics

G enetics. Mitosis & Meiosis. Review p 45-47 A. The Cell Cycle 1 . The dividing cell goes through a cycle of events known as the cell cycle 2 . Cycle divided into interphase and mitosis B . Interphase 1 . Period of DNA replication in preparation of nucleus dividing

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G enetics

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  1. Genetics

  2. Mitosis & Meiosis • Review p 45-47 • A. The Cell Cycle • 1. The dividing cell goes through a cycle of events known as the cell cycle • 2. Cycle divided into interphase and mitosis • B. Interphase • 1. Period of DNA replication in preparation of nucleus dividing • 2. Divided into 3 periods, G1 (1st growth or gap period), S (synthesis), and G2 (2nd growth or gap period)

  3. Mitosis • C. Mitosis • 1.Terms • a.Mitosis= division of the nucleus • b.Cytokinesis= division of the cytoplasm • c.Meristem= regions in plants where mitosis occurs (growing site) • 2.Prophase • a. Chromosomes become shorter, thicker and double move toward equatorial plate • 1) Chromatids • • double threads of chromosomes • 2) Centromeres • • hold chromatids together • 3) Kinetochore • • near centromere, spindle fibers attach here • 4) Other constrictions may occur on individual chromosomes • • called satellites • b. Nucleolus and nuclear envelope disappear • c.Centriolesand asters form (only in algae, fungi, and animal cells)

  4. 3. Metaphase • a. Spindle forms • b. Chromosomes become aligned at the equatorial plate and connect to spindle fiber at the kinetochore (part of the centromere) • 4. Anaphase • a. sister chromatids separate • b. once separated, daughter chromosomes are pulled by the kinetochore along spindle fibers to opposite poles • 5. Telophase • a. Each group of daughter chromosomes becomes surrounded by a new nuclear envelope • b. Daughter chromosomes become longer and thinner • c. New nucleoli appear • d. Phragmoplast appears • e. Cell plate forms • 1) Vesicles from the Golgi fuse to form the cell plate • 2) Plasmodesmata form as ER becomes trapped in cell plate

  5. Phragmoplast

  6. Alternation of Generations review • A. Terminology: n and x • B. Sporophyte Phase (2n) • 1. Diploid (2x) • 2. Meiosis takes place in special spore mother cells (meiocytes) • C. Gametophyte Phase (n) • 1. Haploid (x) • 2. Meiospores begin this phase • 3. Meiospores develop by mitosis into multicellular gametophyte • 4. Gametes are produced which upon fertilization produce the zygote, the first cell of the new sporophyte (2n) phase • D. Many Plant Species Are Polyploid • E. Six Rules Pertaining to Alternation of Generations

  7. Six Rules Pertaining to Alternation of Generations (from the book) • 1. the first cell of any gametophyte generation is normally a spore (sexual spore or meiospore), and the last cell is normally a gamete • 2. any cell of a gametophyte generation (n) is usually haploid (x) • 3. the first cell of any sporophyte generation is normally a zygote, and the last cell is normally a sporocyte (meiocyte)

  8. 4. any cell of a sporophyte generation (2n) is usually diploid (2x) • 5. the change from a sporophyte to a gametophyte generation occurs as a result of meiosis • 6. the change from a gametophyte to a sporophyte generation occurs as a result of fertilization (fusion of gametes) which is also called syngamy

  9. Meiosis • First meiosis • Interphase: replication of DNA and chromosomes • Prophase I: chromosomes of diploid nucleus becomes visible as long thin threads (each consists of 2 chromosomes) • Example: 2 chromosomes with 4 chromotids • 2 homologous pairs of chromosomes

  10. Prophasecont. • Prophase I cont: 2 chromosomes with 4 chromotids • 2 homologous pairs of chromosomes • N = 2

  11. Prophase cont. • Homologues chromosomes pair up (synapses); each chromosome now with 4 chromatids (tetrad) and there is ½ the original number of chromosomes • ========o========== • ========o========== • Above is a tetrad

  12. Prophase cont. • Chromosomes condense as homologous chromatids exchange parts (crossing over)

  13. Prophasecont. • Nuclear membrane disappears • Nucleolus disappears • Homologous chromatids separate at the centramers but remain attached by schismatic

  14. Metaphase I • Paired chromosomes move to equatorial plane • Centromeres of paired chromosomes line up on opposite sides of the equatorial plate

  15. Anaphase I • See above • Homologues chromosomes separate and move toward poles • Two sister chromatids comprise each chromosome • Homologues separate (not the sister chromatids) • Homologs differ because of crossing over

  16. Telophase I • Chromosomes at each pole relax and become elongate and indistinct • Nuclear envelope forms • Nucleoli appear • Each of the two new nuclei have ½ of the original chromosome number • Reduction completed • Cytokinesis may occur or nuclei may proceed immediately to the second division of meiosis

  17. Meiosis II • No additional duplication • Prophase II: nuclear envelope disappears • nucleolus disappears • Metaphase II: chromosomes line up at equator plate • Anaphase II chromatids separate and move to opposite poles • Telophase II: new nuclear envelope and nucleolus reappear

  18. Review

  19. Stop here Wednesday, 7 November 2012

  20. Mendelian Genetics • A. Mendel’s Studies • 1. Austrian monk, born 1822 • 2. Scientific and mathematical studies • 3. Experiments with pea plants • a. Crosses between tall and short plants • b. Crosses between plants with smooth seeds and wrinkled seeds • c. Determination of factors

  21. 4. Law of Unit Characters • factors which always occur in pairs, control the inheritance of various characteristics • Paired factors now known as gene "alleles"

  22. 5. Law of Dominance • in any given pair of factors (alleles), one may suppress or mask the expression of the other • Dominant allele: the expressed factor • Recessive allele: the factor not expressed • Phenotype: what something looks like (pink flowers, wide leaves) • Genotype: • 1) Homozygous: both alleles of a pair are identical (e.g., YY or yy) • 2) Heterozygous: allele pair is composed of contrasting alleles (e.g., Yy) • Incomplete dominance:

  23. 6. Law of Segregation • • members of allele pairs become separated during meiosis • 7. The Monohybrid Cross • a. F2 genotype ratio is 1:2:1 • b. F2 phenotype ratio is 3:1 • 8. The Dihybrid Cross • a. Law of independent assortment • b. Punnett square • c. F2genotype ratio is 1:2:2:4:1:2:1:2:1 • d. F2 phenotype ratio is 9:3:3:1

  24. 9. The Backcross • • between homozygous recessive parent and F1 offspring • 10. Incomplete Dominance • 11. Interactions Among Genes • 12. How Genotype Controls Phenotype • 13. Polyploidy in plants

  25. Incomplete Dominance

  26. How Genotype Controls Phenotype

  27. Polyploidy in plants

  28. Polyploidy in agricultural plants

  29. Science 25 April 2008: Vol. 320 no. 5875 pp. 481-483 • AT SCHOOL: go to Google and put the above into the search line. Print out the article and bring it to class. • We will make plans

  30. Hardy-Weinberg Law • We will go into this in lab.

  31. DNA and RNA • Two kinds of nucleic acids • 1. RNA = ribose nucleic acid • 2. DNA = deoxy ribo nucleic acid

  32. nucleotides

  33. Sugars

  34. D-Ribose 5-phosphate

  35. DNA & RNA • A. Structure of DNA • 1. Nucleotides • a. Nitrogenous base • b. 5-carbon sugar • c. Phosphate group • 2. Nitrogenous bases • a. Purines, adenine and guanine (2 linked rings) • b. Pyrimidines, cytosine and thymine (single ring)

  36. DNA Structure

  37. B. DNA Functions • 1. Storage of Genetic Information • a. A “Gene” molecular unit of of heredity of a living organism • b. Codons and amino acids (see table) • 2. Replication (Duplication) of Information • a. Semi-conservative replication would produce two copies that each contained one of the original strands and one new strand. • b. DNA polymerase • 3. Expression of Information • a. Transcription • b. Translation • 4. Mutation

  38. Codons

  39. DNA polymerase

  40. Transcription

  41. 1. DNA unzips and RNA polymerase enzyme binds to one strand of DNA. • 2. RNA polymerase makes an elongating chain of RNA nucleotides, each new RNA nucleotide is complementary to the DNA nucleotide. • 3. The completed mRNA molecule is released from RNA polymerase - DNA complex and can begin translation. In eukaryotic cells this means first moving from the nucleus into the cytoplasm.

  42. Translation

  43. 1. the ribosome binds to mRNA at a specific area (promoter region) • 2. the ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence • 3. each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain • 4. the ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA • 5. the polypeptide forms into its native shape and starts acting as a functional protein in the cell

  44. Mutations • Somatic: occurs in a body cell and will occur in all cells produced by mitosis • 1. source of new types of horticultural plants • Germ line: occurs in tissue that will produce gametes. • 1. passed on to future generations • 2. important for the genetic improvement of plants (example very sweet corn)

  45. Little Review • DNA • 1. must carry genetic material from cell to cell and form generation to generation. Must carry a great deal of information • 2. must be able to self replicate with great precision • 3. must be able to be modified or changed (mutation) • 4. must have mechanism to read stored information and transfer it into the living system to be used to carry out activities

  46. DNA replication – semi conservative • 1. each strand has ½ of the original strand • 2. after replication both strands are the same 3. occurs in s phase of mitosis • DNA strand is very long to have all of the information • 1. carried on triplicate sequences of DNA • 2. begin reading on a specific sequence • 3 There are 16 combinations of those same 4 bases

  47. Little Review • RNA • Three kinds of RNA • 1. tRNA • 2. rRNA – structural portion, rough ER • 3. mRNA – carries sequences of triplet codes

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