Dihybrid and Monohybrid Crossing

Dihybrid Crossing

• A dihybrid cross is a cross between two pairs of alleles
• "di" means "two"
• Dominant allele (denoted by capital letter, e.g., H) produces a dominant phenotype in individuals who have at least one copy of the allele (Hh or HH)
• Recessive allele (denoted by lowercase letter, e.g., h) produces a recessive phenotype only when both alleles are recessive (hh)

Monohybrid Cross

• A cross between 2 organisms creating different variations
• Only a 25% chance of getting a specific characteristic (like blue eyes)

Gametes

• Gametes (sperm/egg cells) only carry one allele for a gene
• When more than one gene is present, all combinations must be included in the cross

Mendel's Law of Independent Assortment

• Alleles are not linked
• Independent segregation of alleles during gamete formation

Dihybrid Cross Example

• Example of a dihybrid cross: HhSs x hhss
• Use the FOIL method (First, Outside, Inside, Last) to determine the possible gametes

Codominance

• Both alleles are expressed equally
• Neither allele is dominant
• Both alleles contribute to the phenotype, like spots, AB blood type, or flower petal color

Incomplete Dominance

• When both alleles are partially expressed, a "mixed" phenotype (e.g., mesh) is created
• Examples include skin color and flower color