Heredity

• Introduction
  • Definition of Heredity: Transmission of characters/traits from parents to offspring
  • Definition of Variation: Differences among individuals of the same species
  • Importance: Basis of evolution and biodiversity
• Accumulation of Variations
  • Occurs during reproduction
  • Sexual reproduction introduces more variations (due to crossing over and recombination)
  • Asexual reproduction shows minor variations (due to DNA copying errors)
  • Survival advantage: Helps species adapt to changing environments
• Mendel's Laws of Inheritance
  • Gregor Johann Mendel: Father of Genetics
  • Organism studied: Garden Pea (Pisum sativum)
  • Why Pea Plants?
    • Easy to grow
    • Distinct contrasting characters
    • Self-pollinating and cross-pollinating
  • Monohybrid Cross
    • Inheritance of a single gene
    • Cross between tall and dwarf plants
    • $F_1$ Generation: All tall plants (dominant trait expressed)
    • $F_2$ Generation: 3:1 phenotypic ratio, 1:2:1 genotypic ratio
    • Law of Segregation: Alleles separate during gamete formation without blending
  • Dihybrid Cross
    • Inheritance of two genes (e.g., Round/Wrinkled, Yellow/Green seeds)
    • $F_1$ Generation: Round and Yellow (all dominant)
    • $F_2$ Generation: Phenotypic ratio of 9:3:3:1
    • Law of Independent Assortment: Genes for different traits sort independently of one another
• How Do Traits Get Expressed?
  • DNA: Information source for making proteins in the cell
  • Gene: A section of DNA that codes for a specific protein
  • Role of Proteins:
    • Enzymes work efficiently $\rightarrow$ Hormone/trait expressed normally
    • Altered enzyme $\rightarrow$ Less efficient protein $\rightarrow$ Modified trait
  • Sex Determination in Humans
    • Total chromosomes: 23 pairs (22 autosomes + 1 sex chromosome pair)
    • Females: XX (produce eggs with X)
    • Males: XY (produce sperms with X or Y)
    • Determination: Fertilization by X sperm results in Girl (XX); Y sperm results in Boy (XY)
• Key Genetic Terms
  • Trait: Specific characteristic of an organism
  • Allele: Alternative forms of a gene
  • Dominant Trait: Trait that expresses itself in $F_1$ generation (e.g., Tall - T)
  • Recessive Trait: Trait masked in the presence of dominant trait (e.g., Dwarf - t)
  • Genotype: Genetic makeup of an organism (e.g., TT, Tt, tt)
  • Phenotype: Observable physical appearance (e.g., Tall, Dwarf)
  • Homozygous: Identical alleles for a trait (e.g., TT or tt)
  • Heterozygous: Different alleles for a trait (e.g., Tt)