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Genetics Review

Genetics: Fundamentals and Inheritance Patterns

Introduction to Genetics

  • Genetics: The field of biology concerned with heredity, specifically the inheritance of traits between parents and offspring.

Chromosomes, Cell Divisions & Gametes

  • Chromosomes: Units of genetic material that allow for organized sorting during cell division and gamete formation.
    • They contain tightly packed DNA and proteins.
    • A chromosome typically consists of a single, linear, double-stranded DNA molecule and associated chromosomal proteins.
    • After DNA replication (and compaction), a chromosome consists of two sister chromatids joined at the centromere.
  • Counting Chromosomes: The number of centromeres determines the chromosome count. Each chromosome, regardless of whether it has one or two sister chromatids, has one centromere.
    • Centromere: A constricted region on a chromosome, serving as the attachment point for spindle fibers.
    • Sister Chromatids: Two identical copies of a chromosome, joined at the centromere, produced after DNA replication.
    • Telomeres: The specialized structures at the ends of chromosomes.
    • Kinetochore: A protein complex that assembles on the centromere and allows the attachment of microtubules (spindle fibers) during cell division.
  • Cell Types and Ploidy:
    • Somatic cells: Body cells, which are diploid (2n).
    • Diploid (2n): Contains two sets of chromosomes, meaning two of each kind of chromosome.
      • For example, if n=8, then 2n=16 total chromosomes.
    • Homologous Chromosomes: Pairs of chromosomes of the same length and centromere position.
      • They carry the same genes at the same loci, but alleles (different versions of a gene) may differ.
      • One homolog comes from each parent (maternal or paternal).
    • Haploid (n): Contains one set of chromosomes. After meiosis, gametes (sex cells) are haploid and contain only one member of each homologous pair.
  • Genetic Terminology:
    • Loci (singular: Locus): The specific physical location of a gene on a chromosome.
    • Allele: A different version of a gene.
    • Genotype: The specific combination of alleles in an organism.
    • Phenotype: The observable traits or characteristics of an organism, resulting from its genotype and environmental interactions.

Cell Division and the Eukaryotic Cell Cycle

  • Passage of Genetic Material: Cell division is essential for passing genetic material to offspring.
    • Asexual reproduction: Produces daughter cells genetically identical to the parent, typical in unicellular species and bacteria.
    • Sexual reproduction: Produces daughter cells with genetic material from both parent cells, leading to genetic diversity and the formation of gametes.
    • Multicellularity: In multicellular organisms, a single cell must undergo multiple divisions to produce a complete organism.
  • Eukaryotic Cell Cycle: A series of stages that a eukaryotic cell undergoes from the time it receives growth signals until it divides.
    • Interphase: The preparatory phase for cell division, during which the cell grows and DNA is replicated.
      • G_1 (First Gap): Period of cell growth and preparation for division. Contains a