Probability of All Blue-Eyed Children in a Family of Five

Eye color inheritance is polygenic, but a simplified two-gene model (BEY2 for brown/blue, GEY for green/blue) illustrates probabilities.

Scenario 1: Both Parents Heterozygous (Bb)

Each carries one brown (B, dominant) and one blue (b, recessive) allele.

• Probability of blue-eyed child (bb) = ¼ (25%)
• Probability of 5 blue-eyed children = (¼)⁵ = 1/1024 ≈ 0.098% (about 1 in 1,024)

Scenario 2: One Parent Homozygous Blue (bb), Other Heterozygous (Bb)

• Probability of blue-eyed child = ½ (50%)
• Probability of 5 blue-eyed children = (½)⁵ = 1/32 ≈ 3.125% (1 in 32)

Scenario 3: Both Parents Homozygous Blue (bb)

• All children will have blue eyes (100%)

Real-World Complexity

• Multiple genes (OCA2, HERC2, TYR, etc.) interact
• Epistasis, incomplete penetrance, modifier genes
• Conditions like ocular albinism (OCA2 mutations) can cause blue eyes regardless of parental genotype

Genetic counseling can provide personalized risk assessment based on family history and, if desired, genetic testing.