The Science Behind Baby Predictions
OCA2/HERC2 two-gene eye color model, Punnett square implementation, three-generation analysis, and Bayesian reasoning for up to 95% confidence predictions.
Eye Color Genetics
OCA2/HERC2 two-gene model responsible for ~74% of eye color variation
OCA2 Gene (Primary)
Controls melanin production in the iris. Brown (B) allele is fully dominant over blue (b). Located on chromosome 15.
HERC2 Gene (Regulator)
Regulates OCA2 expression. A single SNP in HERC2 determines blue-brown eye color. Green (G) and Amber (A) are modifier alleles.
Punnett Square Engine
Each of the two eye-color genes is solved with its own 2×2 Punnett square (4 outcomes each); the hair-color model uses a 4×4 two-locus grid (16 combinations).
Genotype to Phenotype Mapping
How gene combinations determine eye color
| Genotype | Eye Color | Explanation |
|---|---|---|
| BB | Brown | Homozygous brown — both alleles dominant |
| Bb | Brown | Carries blue but brown is dominant |
| BG | Hazel-Green | Brown + Green modifier |
| GG | Green | Homozygous green |
| Gb | Green | Green dominant over blue |
| bb | Blue | Homozygous recessive — blue eyes |
Polygenic Trait Models
Skin tone and height are controlled by multiple genes
Skin Tone (9+ Genes)
Simplified to 4-allele additive model (D, M, L, V). More dark alleles produce darker skin. Co-dominant blending inheritance.
Height (700+ Genes)
Mid-parental height formula with gender adjustment (boys +6.5cm, girls -6.5cm). Standard deviation of +/-5cm for 68% confidence.
Bayesian Reasoning
Grandparent data constrains genotype possibilities. A blue-eyed grandparent proves the parent carries the recessive allele.
Confidence Scoring
More family data means higher prediction confidence
| Data Available | Confidence | Explanation |
|---|---|---|
| Parents only | 60-70% | Basic Punnett square, no carrier knowledge |
| Parents + 2 grandparents | 90-95% | Partial genotype constraint |
| Parents + 4 grandparents | 95% (capped) | Strong genotype constraint |
| Parents + 4 grandparents | 95% (capped) | Near-certain carrier status |
Prediction Modes
Three modes offering different levels of data input and confidence
| Mode | Credits | Data Required | Confidence |
|---|---|---|---|
| Standard | 8 | Parent traits entered manually (no grandparents) | up to 70% |
| Premium | 12 | Full parent traits + all 4 grandparents | up to 95% |
| Scientific | 4 | Parent traits entered manually (no photos) | up to 65% |
Scientific Validation
Built on peer-reviewed genetic research
Peer-Reviewed Research
Based on Sturm et al. (2008) and Eiberg et al. (2008) for eye color, Lamason et al. (2005) for skin tone, and Lango Allen et al. (2010) for height.
Model Accuracy
OCA2/HERC2 model explains ~74% of eye color variation. Mid-parental height R-squared = 0.71. Polygenic skin tone explains ~60% of variance.
Full Transparency
Every prediction includes confidence scores and Punnett square visualizations so users understand the science behind the results.
Frequently Asked Questions
Common questions about the genetics science behind ProbaBaby
Accuracy depends on the data you provide. Parents only: around 60-65%. With all four grandparents: up to 95% (our hard cap). Our two-gene model explains ~74% of eye color variation.
If a parent has brown eyes, they could be BB (cannot pass blue) or Bb (can pass blue). A blue-eyed grandparent proves the parent is Bb, doubling prediction accuracy for blue-eyed offspring.
The OCA2 gene controls melanin production (brown vs. blue) while HERC2 regulates its expression. Together they account for ~74% of eye color variation, making predictions significantly more accurate than single-gene models.
Skin tone is controlled by 9+ genes. We use a simplified 4-allele additive model where more dark alleles produce darker skin. Unlike eye color, skin tone follows co-dominant blending inheritance.
Height prediction uses mid-parental formula (average parent height +/- 6.5cm for gender). This explains about 71% of height variance with a margin of +/-5cm (68% confidence).
No. ProbaBaby uses simplified genetic models for educational and entertainment purposes. Predictions are probabilities, not guarantees. For diagnostic genetic testing, consult a certified genetic counselor.
Explore Baby Genetics
Download ProbaBaby and discover the science behind baby trait predictions with our two-gene model and three-generation analysis.
- Free to download
- No subscription
- 30+ free tools