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Ch 10: Mendel and Meiosis
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Ch 10: Mendel and Meiosis

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  1. Section 10.1 - Mendel’s Law of Heredity Ch 10: Mendel and Meiosis

  2. Section 10.1 Inside This Section... • Who is Gregor Mendel • Mendel’s Crosses • Phenotypes and Genotypes • Probability in Genetics

  3. Section 10.1 Who is Gregor Mendel? • Known as the father of modern genetics • Developed the principles of heredity by studying the variation and heredity of seven pairs of inherited characteristics in pea plants. • The significance of his work was not recognized during his lifetime.

  4. Section 10.1 Genetics • Genetics is the branch of biology that studies heredity • Heredity is the passing of characteristics from parents to offspring • Traits are inherited characteristics

  5. Section 10.1 More Definitions • Gametes are the sex cells that allow an organism to reproduce • A hybrid is the offspring of parents who have different traits

  6. Section 10.1 Reproduction in Peas • Both male and female parts on the same flower • Male gamete is in the pollen grain • Female gamete is in the ovule (located in the pistil)

  7. Section 10.1 Reproduction in Peas • Pollination is the transfer of male pollen grains to the pistil • Fertilization happens when the male and female gametes unite

  8. F2 Generation F1 Generation Section 10.1 The Generations Parental (P) Generation

  9. The Rule of Factors • Each organism has two factors that control each trait • These factors are called genes and are found on the chromosomes and have alternate forms • The different gene forms that control one trait are called alleles

  10. Section 10.1 Alleles and Genes

  11. Section 10.1 The Rule of Dominance • Dominant: The trait that is more expressive in alleles than other traits (represented by a capital letter) • Recessive: The trait that is submissive in the alleles to the other traits. (Represented by a lowercase letter) • If an organism contains a dominant and a recessive allele, the dominant trait will be expressed TT or Tt tt

  12. Section 10.1 The Rule of Dominance • Phenotype is the physical expression of an organism genes • Genotype is the genetic makeup of an organism TT or Tt tt

  13. Section 10.1 The Law of Segregation • Alleles separate during meiosis • Each new cell gets one allele for each gene TT or Tt tt

  14. Section 10.1 The Law of Independent assortment • All traits are inherited independently from each other

  15. Section 10.1 Two types of Crosses • Monohybrid Cross: A cross in which ALL traits are identical except one • Dihybrid Cross: A cross in which two traits differ between organisms

  16. Section 10.1 F2 - 3 tall : 1 short F1- All Tall P: Parental Generation Mendel’s Monohybrid Cross • When Mendel crossed tall pea plants with short ones, the first generation (F1) consisted of all tall plants • When he crossed the F1 generation, 3/4 of the F2 generation were tall and 1/4 were short

  17. Section 10.1 The Punnett Square T T T t t t • Named after Reginald PunnettUseful for making offspring Predictions • Alleles for 1 parent placed at the top and for the other at the left • Each box is filled with the allele to the top and to the left T T T t t t

  18. Mendel’s Dihybrid Cross • When Mendel crossed Round Yellow peas with wrinkled green peas, all of the F1 generation were Round Yellow Peas • In the F2 generation, the following ratios were found: • 9 Round Yellow • 3 Round Green • 3 Wrinkled Yellow • 1 Wrinkled Green

  19. Section 10.1 rryy rrYy Rryy RrYy rrYy rrYY RRYy RrYy Rryy RrYy RRyy RrYy RrYY RrYY RRYy RRYY Mendel’s Dihybrid Cross RrYy * RrYy ry RY Ry rY RY Ry rY ry Probability & Genetics

  20. Section 10.1 In Review... • Who is Gregor Mendel • Mendel’s Crosses • Phenotypes and Genotypes • Probability in Genetics

  21. Section 10.2 - Meiosis Ch 9: Energy in a Cell

  22. Section 10.2 Section 10.2 Inside This Section... • The Two Types of Cells • Chromosomes and Genes • What is Meiosis? • Genetic Recombination

  23. Section 10.2 Section 10.2 Two Types of Cells • Diploid: A cell with two of each kind of Chromosomes (both alleles for each gene) • We signify this by writing 2n • All cells in the body except sex cells are diploid • Haploid: A cell with one of each kind of Chromosome (only one allele for each gene)We signify this by writing an ”n”Sex cells are Haploid

  24. Section 10.2 Chromosomes and Genes • Chromosomes usually have about a thousand or more genes • Chromosomes occur in pairs • Each chromosome has one allele for a particular gene • Each species contains a characteristic number of chromosomes

  25. Section 10.2 Number of Chromosomes

  26. Section 10.2 What is Meiosis? • A Process of cell division that results in the production of sex cells (gametes) • Consists of • Interphase: Cell replicates chromosomes • Meiosis I: Results in 2 haploid cells • Meiosis II (similar to mitosis): Results in 4 haploid cells

  27. Section 10.2 Meiosis

  28. Section 10.2 Meiosis I • Prophase I • Homologous chromosomes come together and form a tetrad (four-part structure) • Sometimes chromosomes exchange genetic material in a process called crossing over

  29. Section 10.2

  30. Section 10.2 Crossing Over

  31. Section 10.2 Meiosis I • Metaphase I • Spindle fibers cause Homologous Chromosomes to line up side by side at the equator

  32. Section 10.2

  33. Section 10.2 Meiosis I • Anaphase I • Homologous chromosomes separate making each new cell haploid

  34. Section 10.2

  35. Section 10.2 Meiosis I • Telophase I • Reversal of Prophase I • Spindle breaks down, chromosomes uncoil, cytoplasm divides

  36. Section 10.2

  37. Section 10.2 Meiosis II • Identical to Mitosis • Results in 4 Haploid cells

  38. Section 10.2

  39. Section 10.2 Genetic Recombination • Genetic recombination is the source of variation. This is caused by the re-assortment or crossing over during meiosis • 7 pairs of chromosomes = 27 = 128 combinations • Any egg can be fertilized by any sperm, so 128 x 128 = 16,384 possibilities • N=23, 223 = 8,388,608 possibilities • 8,388,608 x 8,388,608 = 7 Trillion possibilities • Crossing over is the exchange of genetic material during prophase I, which results in new combinations of Alleles

  40. Section 10.2 In Review... • The Two Types of Cells • Chromosomes and Genes • What is Meiosis? • Genetic Recombination

  41. Section 10-3: Mistakes in meiosis Ch 9: Energy in a Cell

  42. Section 10.3 Inside This Section... • Nondisjunction • Triploidy and Polyploidy

  43. Section 10.3 Nondisjunction • When chromosomes fail to separate during meiosis. • Trisomy: When one gamete gets an extra chromosome, causing the other gamete to be short by one (e.g. Down’s syndrome - trisomy 21) • Monosomy: When one gamete lacks one chromosome

  44. Section 10.3 Triploidy and Polyploidy • Triploid is a total lack of separation of homologous chromosomes. • Polyploids are organisms that have more than the normal amount of chromosomes • Rare in animals usually causing death • Frequently occurs in plants causing fruit and flowers to be larger

  45. Section 10.3 In Review... • NondisjunctionTriploidy and Polyploidy