Molecular Genetics: Genes, Alleles & Polymorphisms

Core Concepts

  • The lecture briefly delves into basic molecular-genetic terminology needed for later, more detailed chapters.
  • Focuses on how small DNA-level differences create observable human diversity.

Genes vs. Alleles

  • Gene
    • A stretch of DNA coding for a particular biological function (e.g., eye-pigment production).
    • At the population level, most genes are “fixed”—everyone carries the same DNA sequence for that gene.
  • Allele
    • A specific version of a gene.
    • Polymorphic genes have ≥2\ge 2 alleles circulating in the population.
  • Key takeaway: Same gene ⇨ identical overall function; different allele ⇨ slightly different molecular structure, which can shift how that function is expressed (e.g., brown vs. blue eyes).

Genetic Polymorphisms

  • Polymorphism = the existence of two or more alleles at a particular gene locus.
  • Practical meaning:
    • You might inherit allele “A” from one parent, your sibling might inherit allele “B.”
    • These alternative alleles contribute to phenotypic diversity (appearance, physiology, behavior).

Molecular Basis of Allelic Variants

  • Genes are ultimately sequences of nucleotide base pairs (A, T, C, G).
  • Variation mechanisms alluded to in the talk:
    • Single-base substitutions (one nucleotide swapped for another).
    • Repeated bases or repeated sections (short tandem repeats or copy-number variations).
  • Even if the purpose of the gene remains the same, micro-level sequence changes can:
    • Alter the shape of the encoded protein.
    • Modify protein quantity or timing.

Significance of Genetic Variation

  • Provides the raw material for evolutionary processes and individual differences.
  • Explanatory power for traits like eye color, height, metabolism, and disease susceptibility.
  • Without polymorphisms, humanity would be genetically uniform.

Real-World Example Discussed

  • Eye color
    • Governed by pigment-related genes.
    • Brown, blue, green, etc. arise because each allele encodes a slightly different pigment pathway or pigment amount.

Connections & Further Context

  • This short clip is framed as preliminary background; the textbook/next chapter promises deeper dives into:
    • Sequencing technology.
    • Mechanisms that generate new alleles (mutation, recombination).
    • Population genetics (e.g., Hardy–Weinberg equilibrium where p+q=1p + q = 1 for two-allele systems).
  • Ethically, understanding polymorphisms helps in personalized medicine but raises privacy concerns regarding genetic data.