BIOL 1240 Midterm Ultimate Study Guide

Course Logistics and Practice Assessments

• Schedule and Deadlines:

  • Week 7 review is due on Friday.

  • Lecture structure change: A recorded lecture replaces Friday's session with a Wednesday session instead. The recorded video must be viewed and the pre-lecture assignment completed before attending class on Wednesday.

  • A practice assignment covering mitosis, meiosis, and DNA replication is posted under heading 10/2. This assignment is not graded for points.

  • The upcoming exam is scheduled for 10/19 (two weeks out).

• Laboratory and Worksheet Protocol: Mitosis:

  • Cell at metaphase of mitosis: Draw the chromosomes aligned at the metaphase plate. Must include the boundary of the cell, the nucleus (if present), and the specific alleles located on each chromosome.

  • Cell during anaphase of mitosis: Draw the separating chromosomes moving toward opposite poles. Must include the boundary of the cell, the nucleus (if present), and the alleles present on each separating unit.

  • Resulting cells following telophase and cytokinesis: Draw the two resulting daughter cells containing chromosomes still in their chromosome structure. Must include the cell boundaries, the nuclei (if present), and the alleles present on each chromosome.

• Laboratory and Worksheet Protocol: Meiosis and Recombination:

  • Initial state: A germ cell contains the identical chromosome and allele set as represented in the mitosis exercises.

  • Meiotic progression: The germ cell undergoes meiosis to yield 4 gametes with defined allele combinations. To achieve the specific resulting combinations, exactly one crossing over event must take place.

  • Meiosis I - Metaphase: Draw the chromosomes aligned in the cell after the single crossing over event has occurred. Align them specifically to match the configurations required for the final four gametes. Spindle fibers must be drawn explicitly.

  • Meiosis I - Anaphase: Draw the homologous chromosomes separating to opposite poles, maintaining the alignment necessary to yield the specific final gamete combinations. Spindle fibers must be drawn explicitly.

  • Meiosis II - Metaphase: Draw both daughter cells resulting from Meiosis I with chromosomes aligned along the metaphase plate. Maintain allele configurations matching the predetermined ending gametes. Spindle fibers must be drawn explicitly in both cells.

  • Meiosis II Completion: Draw the final 4 separate gamete cells displaying the correct distributed chromosomes and allele combinations.

• Classroom Concept Checks (iClicker):

  • Determining ploidy: Structural criteria explaining why a cell is classified as $2n = 4$.

  • Chromatid relationships: Criteria distinguishing non-sister chromatids from sister chromatids, identifying what non-sister pairs represent (homologous chromosomes).

  • Post-replication metrics: Given 4 initial chromosomes that undergo complete replication, calculate the resulting total chromosome count and the total number of double-stranded DNA molecules present.

Cell Division Mechanisms and Ploidy Dynamics

• Ploidy Fundamentals:

  • Haploid ($n$): A state characterized by containing exactly 1 copy of each unique chromosome.

  • Diploid ($2n$): A state characterized by containing 2 copies of each unique chromosome (homologous pairs).

• Ploidy Preservation and Reduction across Division Types:

  • Binary Fission: Preserves ploidy state ($n \rightarrow n$).

  • Mitosis: Preserves parental ploidy state ($2n \rightarrow 2n$ or $n \rightarrow n$).

  • Meiosis: Reduces ploidy state by half ($2n \rightarrow n$).

• Mechanism of Bacterial Binary Fission:

  • Step 1 (DNA Replication and Filament Attachment): Original DNA is replicated by replication enzymes to generate new DNA. Protein filaments attach to the DNA copies.

  • Step 2 (Separation and Ring Formation): DNA copies are segregated toward opposite ends of the cell while a ring of protein forms at the mid-cell boundary.

  • Step 3 (Membrane Constriction): The protein ring constricts, drawing the cell membrane inward.

  • Step 4 (Fission Completion): Septation and membrane closure finish, dividing the single bacterial cell into two distinct cells.

• Stages of Mitosis versus Meiosis:

  • Mitosis Pathway:

    • Initiates from a diploid parent cell ($2n$).

    • Chromosome replication produces sister chromatid pairs.

    • Prophase: Chromatin condenses.

    • Metaphase: Chromosomes align along the central equatorial plate.

    • Anaphase and Telophase: Sister chromatids separate to opposite poles, followed by nuclear reconstitution and cytokinesis.

    • Outcome: Yields two genetically identical diploid ($2n$) daughter cells.

  • Meiosis Pathway:

    • Initiates from a diploid parent cell ($2n$).

    • Chromosome replication occurs prior to entry into Meiosis I.

    • Prophase I: Homologous chromosomes pair up and undergo genetic recombination (crossing over).

    • Metaphase I: Homologous pairs line up on the metaphase plate.

    • Anaphase I and Telophase I: Homologous chromosome pairs separate into two intermediate cells.

    • Meiosis II: Sister chromatids separate in both intermediate cells.

    • Outcome: Yields four genetically distinct haploid ($n$) daughter cells (gametes).

Reproductive Strategies: Sexual versus Asexual

• Core Learning Objectives (BIOL 1240):

  • Compare and contrast the biological mechanisms and developmental outcomes of sexual and asexual reproduction.

  • Identify the relative evolutionary and energetic advantages and disadvantages of sexual versus asexual reproductive modes.

  • Interpret the generalized life cycles of eukaryotic organisms, specifically haplontic, diplontic, and alternation of generations cycles.

• Mechanistic Distinctions:

  • Sexual Reproduction:

    • Involves the fusion (syngamy/fertilization) of haploid gametes.

    • Fundamentally reliant on the process of meiosis to produce gametes.

    • Generates progeny that are genetically distinct from both parent organisms and from siblings.

  • Asexual Reproduction:

    • Occurs without the fusion of gametes.

    • Primarily mediated by mitosis-based mechanisms or binary fission.

    • Offspring inherit genetic material exclusively from a single parent.

    • Offspring are clones, meaning they are genetically identical to the parent organism and to one another in almost all circumstances.

Modes of Asexual Reproduction Across Taxa

• Single-Celled Organisms:

  • Prokaryotes: Reproduce exclusively through binary fission ($n \rightarrow n$).

  • Eukaryotes: Utilize mitosis-driven processes, such as budding observed in single-celled fungi like yeast.

• Multicellular Plants:

  • Widespread Occurrence: Extremely common across diverse botanical taxa.

  • Genomic Totipotency: Enabled by the fact that all nuclear DNA is conserved within every somatic cell of the multicellular body, allowing somatic tissues to regenerate entire organismal structures.

  • Vegetative Mechanisms:

    • Rhizomes: Underground stem modifications that grow horizontally to generate new clonal shoots.

    • Plantlets: Miniature vegetative structures produced along mature leaves or stems that drop off and root independently.

• Multicellular Animals:

  • Overall Frequency: Relatively rare across the animal kingdom, but present in specialized lineages.

  • Budding in Cnidarians:

    • Corals: Sexual reproduction initially produces a mobile polyp. That primary polyp subsequently multiplies asexually via budding to generate a colonial aggregate of genetically identical polyps. Continued budding builds massive coral colonies that form the core structure of coral-reef ecosystems.

    • Hydra: Generates outgrowth buds directly from the parental body column that detach as independent individuals.

  • Fragmentation (Often termed Fission):

    • Sea stars: Body fragments sever and regenerate complete morphological structures into whole individuals.

    • Flatworms: Physical division or self-induced fragmentation along the body axis followed by cellular regeneration.

    • Terminological Caveat: While fragmentation in invertebrates is frequently referred to as fission, it must not be conflated with prokaryotic binary fission.

  • Parthenogenesis ("Virgin-Birth"):

    • Defined as the process wherein females produce egg cells that develop into viable organisms without fertilization by male sperm.

    • Egg generation typically occurs via meiosis, though in rare biological exceptions it occurs via mitosis.

    • Mechanism: Haploid egg cells duplicate their genome (or fuse with a polar body) to establish diploidy and initiate embryonic development in the complete absence of fertilization.

    • Classified strictly as asexual reproduction because it eliminates fertilization by a male parent.

    • Occurrence: Fairly rare among vertebrates.

    • Documented Examples: Fatherless boa constrictors and Komodo dragons.