Monohybrid Cross & Complete Dominance

Rucete ✏ Biology In a Nutshell

1. Complete Dominance

• In complete dominance, the dominant allele completely masks the recessive allele in the phenotype.
• Only one dominant allele is needed to express the dominant trait.
• Example:
  • P (purple flower) = dominant
  • p (white flower) = recessive
  • Genotypes:
    • PP or Pp = purple
    • pp = white

2. Monohybrid Cross

• A monohybrid cross examines the inheritance of one trait.
• Involves crossing individuals that are heterozygous for a single trait.

3. Generations in a Monohybrid Cross

P Generation (Parental)

• Cross between homozygous dominant (PP) and homozygous recessive (pp).
• All offspring (F₁) are heterozygous (Pp) and show the dominant phenotype.

F₁ Generation (First Filial)

• All offspring are Pp (purple flowers).

F₂ Generation (Second Filial)

• F₁ × F₁ → Pp × Pp
• Genotype ratio: 1 PP : 2 Pp : 1 pp
• Phenotype ratio: 3 purple : 1 white

4. Key Vocabulary

• Allele: Different forms of a gene (e.g., P or p)
• Genotype: Genetic makeup (PP, Pp, or pp)
• Phenotype: Physical trait expressed (purple or white flower)