Biology Meiosis Overview Part I-C (Exam 1)

Time Management vs. Focus

• Time is not a problem, focus is.
• Images of clocks show a difference between sufficient time and lack of focus.

Meiosis in Eukaryotes

• Meiosis is a reproductive process for eukaryotic organisms.

Meiosis in Mammals

• Males: Produce 4 sperm cells continuously after puberty.
• Females: Begin meiosis in the fetus, completing it with fertilization.
  • Produces 1 oocyte and 2 polar bodies.

Meiosis

• A reductive division to produce separate genetically distinct haploid gametes.

Chromosome Terminology

• Homologous chromosomes: A pair of chromosomes in a diploid organism that have:
  • Almost identical DNA sequences.
  • Same genes in the same location (locus).
  • Same size.
  • Centromere in the same location.
• Unreplicated chromosomes: A single pair of chromosomes.
  • 2 chromosomes.
  • 2 double stranded DNA molecules (1 per chromosome).
• Replicated chromosomes: A copied pair of chromosomes
  • 2 replicated chromosomes.
  • 4 double stranded DNA molecules.
  • Each is made of 2 sister chromatids.

Structure of the Synaptonemal Complex

• Diagram showing different stages (Leptotene, Zygotene, Pachytene, Diplotene) of the synaptonemal complex.
• Contains components such as Axial Elements, Transverse Elements, and Central Element.

Early Prophase I

• Chromosomes condense, synapse, and recombination begins.
• Replicated chromatin is packed onto the axial elements
• Recombination hotspots are found and DSBs occur
• Telomeres anchor to the nuclear envelope for homologous pairing, aligning axes together.

Prophase I: Homologues Pair

• Homologous chromosomes pair.
• Synapsis proceeds along the length of the chromosome.
• DSB repairs allow recombination.
• Most breaks=non-crossover events
• Minority=crossover events.
• Transverse filaments(green), bind the central element (red) of homologous chromosomes.

Prophase I: Fully Synapse

• Chromosomes are fully synapsed.
• Recombination is finalized with DSB repairs.
• Proteins are involved in DSBs and repair.

Prophase I: Desynapse

• Synaptonemal complex disassembled.
• Homologous chromosomes held together by chiasmata.

Meiosis I: Reductional Division

• Prophase I: Replication chromosomes condense, synapse, crossing over, nuclear envelope breaks down.

• Metaphase I: Homologous pairs are aligned by spindle fibers.

• Anaphase I: Homologues separate to opposite poles.

• Telophase I & Cytokinesis: Cytoplasm divides, may reform nuclear envelopes and chromosomes decondense.

• C value: The number of chromosomes, and the number of DNA molecules.

Meiosis II: Equational Division

• Prophase II: Chromosomes condense, new spindle forms. Nuclear envelope breaks down.
• Metaphase II: Replicated chromosomes align at the metaphase plate.
• Anaphase II: Sister chromatids separate to opposite poles.
• Telophase II, Cytokinesis: Chromosomes arrive at the poles, nuclear envelope forms, and cytoplasm divides.

Meiosis: Unique Cells

• Product = 4 cells

• Chromosome number is halved (2n → n)

• Cells are genetically different

• Recombination: Exchange of DNA between non-sister chromatids.

• Random alignment (Metaphase I and II): Allows assortment and shuffling of chromosomes.

• Random distribution: Random placement of maternal and paternal chromosomes.

Random Alignment on Metaphase Plate

• Diagram showing different possible combinations from random alignment in metaphase I.
• 8 possible combinations in gametes.

Cell Cycle (Eukaryotes)

• Diagram showing stages in a circle.
• Shows mitosis (Prophase, Metaphase, Anaphase, Telophase, Cytokinesis)
• Includes DNA replication in the Interphase Stages: G₁, S, G₂, and G₀.

Synaptonemal Complex- Detailed View

• Diagram illustrating the complex structure and components of the synaptonemal complex.

This quiz covers essential concepts related to meiosis in eukaryotes and mammals, including the stages and outcomes of meiosis. It also explores chromosome terminology and differences between homologous, unreplicated, and replicated chromosomes. Test your knowledge on these crucial biological processes!