Biology Semester Review 2024-2025 (3)

Genetics

  • Alleles

    • Dominant alleles: Represented by capital letters (e.g., Black hair is dominant (B)).

    • Recessive alleles: Represented by lower-case letters (e.g., Red hair is recessive (b)).

    • Genotype: Combination of alleles from parents (e.g., Bb).

    • Example: Stephanie is left-handed (recessive trait, r), with parents being heterozygous carriers (Bb).

  • Homozygous vs Heterozygous

    • Homozygous: Same alleles (BB or bb).

    • Heterozygous: One dominant and one recessive allele (Bb, also known as a Carrier).

    • Dominant traits are displayed with one dominant allele. Recessive traits are displayed only with two recessive alleles (bb).

Codominant and Incomplete Dominance

  • Codominance: Both traits are fully expressed.

    • Example in cows: Cross between WW (white) and BB (black) results in a white cow with black spots.

    • Genotype combinations can be determined using the FOIL method: First, Outer, Inner, Last.

  • Incomplete Dominance: Traits blend.

    • Example: Red flower (RR) mixed with white flower (rr) results in pink flowers (Rr).

DNA Structure

  • DNA (Deoxyribonucleic Acid): Genetic material for all living things.

    • Backbone: Alternating deoxyribose sugar and phosphate groups.

  • Nitrogenous Bases: A, T, C, G (Adenine, Thymine, Cytosine, Guanine).

    • Base pairing rule: A pairs with T (Apple in the Tree), C pairs with G (Car in the Garage).

    • Nucleotide: Combination of deoxyribose sugar, phosphate group, and a nitrogenous base.

Protein Synthesis

  • Stages of Protein Synthesis:

    1. Transcription: mRNA is produced from DNA. Thymine is replaced with Uracil (U).

    2. Translation: mRNA is used to build amino acid chains using help from tRNA and ribosomes.

  • Codon: A sequence of three mRNA nucleotides (e.g., UAG).

  • Example: DNA sequence GAA-CCT-ACT transcribes to mRNA CUU-GGA-UGA, leading to amino acids Leu-Gly-Stop Codon.

Genetic Expression and Mutations

  • Environmental Influence: Genetic expression may be affected by external factors, e.g., Snowshoe hares changing fur color due to seasonal shifts.

  • Genetic Mutations: Changes in DNA or mRNA that can alter traits.

    • Types of Mutations:

      • Substitution/Point Mutation: One nucleotide replaced by another.

      • Insertion Mutation: Extra nucleotides added.

      • Deletion Mutation: Nucleotides removed.

Chromosomes and Cell Transport

  • Chromosomes: Made of condensed DNA; crossing over during meiosis promotes genetic diversity.

  • Cell Membrane Function: Manages the movement of substances in and out of the cell.

    • Passive Transport: Moves with the gradient (no energy required).

    • Active Transport: Moves against the gradient (requires energy, ATP).

Types of Solutions

  • Hypotonic Solution: More solute inside the cell; causes swelling.

  • Hypertonic Solution: More solute outside the cell; causes shriveling.

  • Isotonic Solution: Equal solute concentrations inside and outside.

Photosynthesis vs. Cell Respiration

  • Photosynthesis: Uses sunlight to create glucose; requires carbon dioxide, water, and light.

  • Cell Respiration: Converts glucose into ATP; products of photosynthesis serve as reactants.

The Cell Cycle

  • Main Steps:

    1. Interphase (G0, G1, S, G2)

    2. Mitosis (Prophase, Metaphase, Anaphase, Telophase).

  • Cancer Cells: Uncontrolled cell cycle leading to tumors.

Biomolecules

  • Proteins: Essential for chemical processes; include enzymes and structural proteins (e.g., keratin).

  • Carbohydrates: Main energy source (sugars, starches).

  • Lipids: Long-term energy, insulation, and cell membrane structure (fats).

  • Nucleic Acids: Genetic materials; DNA and RNA.

Cells Comparison

  • Eukaryotes: Complex cells with a nucleus and organelles.

  • Prokaryotes: Simpler cells without organelles or a nucleus.

  • Ribosomes: Sites of protein synthesis; endoplasmic reticulum aids in intercellular transport.