Meiosis Notes

Meiosis Learning Objectives

  • Identify how many sets of genes are found in most adult organisms.
  • Describe the events that occur during each phase of meiosis.
  • Identify the differences between meiosis and mitosis.
  • Explain how two alleles from different genes can be inherited together.

Chromosome Number

  • Homologous Chromosomes: Chromosomes with the same genes, one originally from each of the organism’s parents.
  • Diploid (2N): Containing both sets of homologous chromosomes.
  • Haploid (1N): Containing only a single set of chromosomes.

Reviewing Mitosis

  • Mitosis Phases:
    • Prophase
    • Metaphase
    • Anaphase
    • Telophase

Meiosis Overview

  • MEIOSIS I
    • Interphase: Precedes Meiosis I.
    • Prophase I: Includes crossing-over.
    • Metaphase I
    • Anaphase I
    • Telophase I and Cytokinesis: Results in two cells with two replicated chromosomes.
  • MEIOSIS II
    • Prophase II
    • Metaphase II
    • Anaphase II
    • Telophase II and Cytokinesis: Results in four haploid daughter cells.

Prophase I

  • Key events:
    • Spindle forming.
    • Nuclear envelope breakdown.
    • Centrioles present.
    • Crossing Over: Genetic material exchange.
    • Tetrads: Formed by homologous chromosomes.
    • Chromosomes visible.
    • Centromere.

Metaphase I

  • Pair of homologous chromosomes align.

Anaphase I

  • Sister chromatids present.

Telophase I and Cytokinesis

  • Nuclear envelopes reforming.

Prophase II

  • Starts with two cells, each containing two replicated chromosomes.

Metaphase II and Anaphase II

  • Metaphase II
  • Anaphase II

Telophase II and Cytokinesis

  • The end result of meiosis is four daughter cells.
  • These daughter cells have half the normal chromosome number.

Summary of Meiosis

  • Interphase: Precedes Meiosis I.
  • MEIOSIS I
    • Prophase I: Crossing-over occurs.
    • Metaphase I
    • Anaphase I
    • Telophase I and Cytokinesis: Results in two cells with two replicated chromosomes.
  • MEIOSIS II
    • Prophase II
    • Metaphase II
    • Anaphase II
    • Telophase II and Cytokinesis : Results in four haploid daughter cells.

Comparing Mitosis and Meiosis

  • Meiosis I phases: prophase I, metaphase I, anaphase I, telophase I and cytokinesis.
  • Example:
    • 2N = 4
    • N = 2

Gene Linkage

  • Alleles of different genes tend to be inherited together when those genes are located on the same chromosome.

Gene Maps (Chromosome 2 Example)

  • Location of Genes on Chromosome 2:
    • 0.0: Aristaless (no bristles on antenna)
    • 1.3: Star eye
    • 13.0: Dumpy wing
    • 31.0: Dachs (short legs)
    • 48.5: Black body
    • 51.0: Reduced bristles
    • 54.5: Purple eye
    • 55.0: Light eye
    • 57.5: Cinnabar eye
    • 67.0: Vestigial (small) wing
    • 75.5: Curved wing
    • 99.2: Arc (bent wings)
    • 104.5: Brown eye
    • 107.0: Speck body