Mendelian Genetics

Modes of Phenotypic Expression

  • Genotype influences phenotype through the relationship between dominant and recessive alleles.

Key Definitions

  • Genotype: Genetic makeup (e.g., WW, Ww, ww)

  • Phenotype: Physical expression (e.g., Dominant W, Recessive w)

Examples of Disorders

  • Cystic Fibrosis

    • Dominant: F (normal), Recessive: f (cystic fibrosis)

    • Alleles: FF (normal), Ff (carrier), ff (has condition)

  • Achondroplasia

    • Dominant: A (achondroplasia), Recessive: a (not achondroplasia)

    • Outcomes: AA (fatal), Aa (affected), aa (not affected)

  • Sickle-Cell Disease

    • A1 (normal), A2 (deformed)

    • Co-dominance observed with genotypes: A1A1 (normal), A1A2 (sickle-cell carrier), A2A2 (disease)

Heterozygote Advantage

  • A1A1: Normal, susceptible to malaria

  • A1A2: Sickle-cell carrier, provides partial protection from malaria

  • A2A2: Sickle-cell disease, lower malaria susceptibility

Pedigree Analysis

  • Analyzing inheritance patterns in families, e.g., the Potter family tree.

Probability in Genetics

  • Uses multiplication law for independent events.

    • E.g., calculating probability for multiple offspring traits:

    • Probability for single child being mm: 1/4

    • For multiple children, e.g., 3 children being mm: (1/4)^3 = 1/64

Misconceptions

  1. Dominant traits are not necessarily more likely to be inherited.

  2. Dominance does not imply prevalence in a population.

  3. Both dominant and recessive alleles can be expressed.

Polygenic Inheritance

  • Traits determined by multiple genes, leading to a range of phenotypes (e.g., skin color, height).

Eye Color as Polygenic

  • Influenced by up to 15 genes, with variations due to pigment and light scattering.

  • Genotype influences phenotype through dominant and recessive alleles.

  • Key Definitions: Genotype (genetic makeup), Phenotype (physical expression).

  • Disorders:

    • Cystic Fibrosis: F (normal), f (cystic fibrosis); FF (normal), Ff (carrier), ff (has condition).

    • Achondroplasia: A (achondroplasia), a (not achondroplasia); AA (fatal), Aa (affected), aa (not affected).

    • Sickle-Cell Disease: A1 (normal), A2 (deformed); A1A1 (normal), A1A2 (carrier), A2A2 (disease).

  • Heterozygote Advantage: A1A2 provides partial malaria protection.

  • Pedigree Analysis: Assesses inheritance patterns within families.

  • Probability in Genetics: Uses multiplication law; for single child being mm: 1/4, for 3 children being mm: (1/4)^3 = 1/64 .

  • Misconceptions: Dominance does not guarantee inheritance, prevalence; both alleles can express.

  • Polygenic Inheritance: Traits influenced by multiple genes (e.g., height, skin color).

  • Eye Color: Determined by up to 15 genes with variations from pigment and light scattering.