Phenotype Probability Calculator
Calculate the probability of offspring inheriting specific traits. Select parent phenotypes to see the likelihood of different trait combinations in their children.
Note: Eye color is actually polygenic (controlled by multiple genes), but this simplified model shows the basic inheritance pattern.
Note: This shows simplified brown vs. blonde inheritance. Real hair color involves multiple genes.
About Widow's Peak: A V-shaped point in the hairline. Presence is dominant over absence.
About Earlobes: Free (unattached) earlobes are dominant over attached earlobes.
About Tongue Rolling: The ability to roll your tongue into a U-shape is traditionally considered dominant, though recent research suggests it may be more complex.
About Dimples: Facial dimples are considered a dominant trait.
Offspring Trait Probabilities
Detailed Genetic Breakdown
| Genotype | Phenotype | Probability | Percentage |
|---|
Visual Probability Distribution
Punnett Square
Summary
⚠️ Important Note
These calculations are based on simplified Mendelian genetics. Real human traits are often more complex, involving multiple genes (polygenic inheritance), environmental factors, and gene interactions. Use this calculator for educational purposes and basic probability estimates only.
Understanding Trait Probability
Phenotype probability refers to the likelihood that offspring will display a particular observable trait based on their parents' genetic makeup. While genetics provides probabilities, each child is a unique combination of their parents' genes.
How Probability Works in Genetics
Independent Events
Each child's genetic makeup is an independent event. If there's a 25% chance of blue eyes, this doesn't mean 1 in every 4 children will have blue eyes - each child has that same 25% chance independently.
Dominance Patterns
Most traits shown here follow complete dominance, where one allele masks the other:
- • AA or Aa = Dominant phenotype expressed
- • aa = Recessive phenotype expressed
- • Heterozygotes (Aa) look like homozygous dominant (AA)
Carrier Status
Individuals with heterozygous genotype (Aa) are "carriers" of the recessive allele. They show the dominant trait but can pass the recessive allele to offspring. Two carriers (Aa × Aa) have a 25% chance of a child with the recessive trait.
Common Human Traits and Their Genetics
Eye Color
Reality: Polygenic (multiple genes, especially OCA2 and HERC2)
Simplified Model: Brown dominant over blue
- • Two brown-eyed parents can have blue-eyed child (if both Bb)
- • Two blue-eyed parents (bb × bb) = all blue-eyed children
- • Green and hazel eyes involve additional genetic factors
Hair Color
Reality: Highly polygenic (many genes involved)
Simplified Model: Dark dominant over light
- • Red hair is usually recessive and requires specific genes
- • Black, brown, blonde, and red have different genetic bases
- • Hair color can change with age
Widow's Peak
Pattern: V-shaped hairline point
Inheritance: Presence dominant over absence
- • W (widow's peak) dominant over w (straight hairline)
- • WW or Ww = has widow's peak
- • ww = straight hairline
Earlobe Attachment
Pattern: Free vs. attached to side of head
Inheritance: Free dominant over attached
- • E (free) dominant over e (attached)
- • EE or Ee = free earlobes
- • ee = attached earlobes
Tongue Rolling
Pattern: Ability to roll tongue into U-shape
Note: Inheritance more complex than once thought
- • Originally thought to be single-gene dominant trait
- • Recent research suggests environmental learning involved
- • Still useful for teaching genetics concepts
Dimples
Pattern: Indentations in cheeks when smiling
Inheritance: Presence dominant over absence
- • D (dimples) dominant over d (no dimples)
- • DD or Dd = has dimples
- • dd = no dimples
Understanding Probability Outcomes
Scenario 1: Both Parents Heterozygous (Bb × Bb)
Most common scenario for recessive traits appearing
Outcomes:
• 25% chance of BB (homozygous dominant)
• 50% chance of Bb (heterozygous, carrier)
• 25% chance of bb (homozygous recessive)
Phenotypes: 75% dominant, 25% recessive (3:1 ratio)
Scenario 2: One Homozygous, One Heterozygous (BB × Bb)
Guaranteed dominant phenotype, but carriers possible
Outcomes:
• 50% chance of BB (homozygous dominant)
• 50% chance of Bb (heterozygous, carrier)
• 0% chance of bb
Phenotypes: 100% dominant (no recessive trait possible)
Scenario 3: Both Parents Homozygous Recessive (bb × bb)
All offspring will have recessive trait
Outcomes:
• 0% chance of BB
• 0% chance of Bb
• 100% chance of bb (homozygous recessive)
Phenotypes: 100% recessive (no dominant trait possible)
References
Information about human traits and genetic inheritance patterns:
Related Calculators
Important Disclaimer: This calculator provides simplified probability estimates for educational purposes. Real human trait inheritance is usually much more complex than single-gene Mendelian genetics. Most traits like eye color, hair color, and height are polygenic (controlled by multiple genes) and influenced by environmental factors. The probabilities shown here are approximations based on simplified genetic models. For actual genetic counseling, family planning, or medical genetics questions, please consult qualified healthcare professionals or genetic counselors.
Recommended Calculator
Casio FX-991ES Plus
The professional-grade scientific calculator with 417 functions, natural display, and solar power. Perfect for students and professionals.
View on Amazon