Key Concepts on Genotype and Phenotype

  • Lecture Focus: Understanding how genotype gives rise to phenotype through protein function.

  • Key Terms:

    • Genotype: Genetic constitution of an individual.
    • Phenotype: Observable characteristics resulting from genotype.
    • Allele: Different forms of a gene.
    • Central Dogma: DNA → mRNA → Protein.

  • Lecture Objectives:

    • Refresh on Punnett squares and probability regarding monohybrid crosses.
    • Understand ratios for phenotype (3:1) and genotype (1 RR: 2 Rr: 1 rr).
    • Know about biallelic expression, loss of function (lof), and gain of function (gof) mutants.
    • Distinguish dominance from wild type
    • Dominance doesn't imply "better" allele.

  • Monohybrid Cross: A genetic cross involving one gene.

    • Only applies to traits with complete dominance.

  • Phenotype Interaction:

    • Dominant alleles (RR, Rr) express wet earwax.
    • Recessive alleles (rr) express dry earwax.

  • Gene Function:

    • Genes encode proteins, which dictate phenotype.
    • Example: abcc11 gene → mRNA → polypeptide → ABCC11 protein responsible for cerumen transport.

  • Mutations:

    • Mutations vary in impact; can be silent, missense, frameshift, or nonsense.
    • Loss of function (lof) mutants may produce no or non-functional proteins.

  • PKD Example:

    • A disease where one lof allele can disrupt function, indicating it isn't necessarily recessive.

  • Functionality of Proteins:

    • Proper folding and location are crucial for function.
    • Gain of function mutations can lead to abnormal functions, e.g., autoimmune diseases.

  • Important Concepts:

    • Dominant phenotype needs only one dominant allele.
    • Recessive phenotype requires two recessive alleles.
    • Key Takeaway: The function of proteins produced by the alleles determines the observable phenotype.