Biology Mitosis and Genetics Review

Examination IV Biology Study Notes

Gene:
- Definition: The units of information that specify an organism’s inherited traits.
- Location: Found in the cell nucleus, grouped into multiple chromosomes.
Chromosomes:
- Definition: Structures consisting of DNA and proteins (histones) packed together.
- Composition: Each eukaryotic chromosome consists of one long DNA molecule and various protein molecules that help maintain chromosome structure and regulate gene activity.
- Location: Present in the nucleus of eukaryotic cells as chromatin; condense during cell division.
- Formation:
- DNA wraps around histone proteins to form nucleosomes.
- These coil and fold to form condensed chromosomes.
Purpose of Chromosome Condensation:
- Makes DNA easier to move during cell division.
- Organized packaging helps prevent DNA from breaking, tangling, and ensures equal distribution.
- Each chromosome consists of two copies, called sister chromatids, joined at the centromere.
- Sister chromatids form during the S phase of the cell cycle.
Cell Division:
- Importance: All life depends on cell division for reproduction, growth to adult size, and replacement of damaged cells.
- The cell cycle is an ordered sequence of events from the formation of a cell until its division into two cells.

Chromosome Division:
- Essential to ensure each new cell receives identical DNA for growth, repair, and distribution.
- Each daughter cell receives a complete and identical set of chromosomes.
Cell Cycle Phases:
- The cell cycle consists of:
1. Interphase
  - Preceding division stage; high metabolic activity.
  - Phases:
    - G1 (First Gap): The cell grows.
    - S (Synthesis): DNA replication occurs, doubling each chromosome.
    - G2 (Second Gap): Cell prepares for division.
2. Mitosis (Mitotic Phase):
  - Division of the cell nucleus, producing two genetically identical daughter cells.
  - Stages of Mitosis:
  1. Prophase:
    - Chromatin condenses to form visible chromosomes.
    - Each chromosome has two sister chromatids.
    - The nuclear envelope breaks down, and spindle fibers begin to form.
  2. Prometaphase:
    - Nuclear envelope disintegrates.
    - Spindle microtubules attach to kinetochores on chromatids.
  3. Metaphase:
    - Chromosomes align at the metaphase plate.
    - Kinetochores attach to spindle fibers from opposite poles.
  4. Anaphase:
    - Sister chromatids separate and move toward opposite poles of the cell via motor proteins.
  5. Telophase:
    - Nuclear envelopes reform around the two sets of chromosomes.
    - Chromosomes decondense back to chromatin.
3. Cytokinesis:
  - Division of the cytoplasm, results in two distinct daughter cells.
  - In animal cells, cleavage furrow pinches the cell into two.

Meiosis:
- Function: Produces four genetically different haploid cells (gametes) from one diploid parent cell.
- Importance: Produces gametes and creates genetic variation.
- Key Features:
- Two rounds of cell division (Meiosis I and II).
- Includes crossing over and independent assortment.
Differences Between Mitosis and Meiosis:
- Mitosis produces two genetically identical diploid cells, while meiosis produces four genetically different haploid cells.
- Mitosis involves one division, meiosis involves two.
Cells Undergoing Mitosis and Meiosis:
- Mitosis occurs in somatic cells (e.g., skin, muscle, liver).
- Meiosis occurs in germ cells in reproductive organs.

Meiosis I (Reduction Division):
- Prophase I: Homologous chromosomes pair to form tetrads, crossing over occurs.
- Metaphase I: Tetrads align at center; independent assortment occurs.
- Anaphase I: Homologous chromosomes separate to opposite poles.
- Telophase I & Cytokinesis: Two haploid cells form.
Meiosis II: Similar to mitosis, where sister chromatids separate to produce four haploid cells.

Genetic Variability in Meiosis:
- Created through crossing over in Prophase I and independent assortment in Metaphase I.
- Punnett Squares:
- Monohybrid: A cross for one trait; calculate genotype and phenotype ratios.
- Dihybrid: A cross for two traits, requires a 4×4 Punnett square.
Dominant and Recessive Traits:
- Dominant Allele: Expressed in AA or Aa.
- Recessive Allele: Expressed only in aa.

Understanding Pedigrees:
- Used to track inheritance patterns of traits. Importantly identifies dominant vs. recessive and autosomal vs. sex-linked traits.
Key Rules for Inheritance:
- Dominance is evident in each generation, while recessive traits may skip generations.

DNA Structure:
- Composed of nucleotides: sugar, phosphate group, and nitrogenous bases.
- Function: Carries instructions for protein synthesis; organized into chromosomes.
DNA Replication:
- Semiconservative process: Each new DNA molecule contains one original and one new strand.
- Process includes helicase (unwinding DNA), primase (adding primer), DNA polymerase (building new strands), and ligase (joining fragments).
Central Dogma of Molecular Biology:
- Describes the flow of genetic information: DNA → RNA → Protein.
- Transcription: Synthesis of mRNA in the nucleus.
- Translation: mRNA to protein at ribosomes.
Mutation Types:
- Silent Mutation: No effect on protein.
- Missense Mutation: Results in a different amino acid.
- Nonsense Mutation: Premature stop codon.
- Frameshift Mutation: Caused by insertions or deletions not in multiples of three.

Important Vocabulary: