Introduction to heredity review (article) | Khan Academy

Key Concepts in Heredity

• Core Definitions:
  • Genetics: The study of biological inheritance.
  • Gene: The unit of heredity passed from parent to offspring.
  • Allele: Different forms of a specific gene.
  • Genotype: The genetic makeup (e.g., TT).
  • Phenotype: The physical expression of traits (e.g., tall).
  • Homozygous vs. Heterozygous: Having two identical alleles versus two different alleles for a gene.
• Dominant vs. Recessive:
  • Dominant: Expressed over another allele; typically produces a functional protein.
  • Recessive: Only expressed in the absence of a dominant allele; often results from a loss-of-function mutation where the protein produced is non-functional or less functional.
• Tools and Methods:
  • Punnett Square: A diagram used to predict the genotypes and phenotypes resulting from a genetic cross.
  • Mendelian Inheritance: The foundational laws governing how traits are passed down.
• Common Misconceptions:
  • Dominance ≠ Frequency: A dominant trait is not necessarily the most common trait in a population (e.g., Huntington's disease).
  • Complexity of Traits: Many traits are polygenic (controlled by multiple genes) rather than the product of a single gene (e.g., human eye color).
  • Allelic Variety: Some genes have more than two possible alleles (e.g., cat coat color).