Why This Guide Exists
Mewgenics markets itself as having Mendelian genetics, but the actual breeding system is more nuanced than simple dominant/recessive traits. The community has reverse-engineered the exact formulas (credit to SciresM's decompilation of glaiel::CatData::breed), and this guide presents them in a practical format with probability tables you can reference during gameplay.
Most other guides say "higher Stimulation = better inheritance." This guide gives you the exact numbers.
The Core Variable: Stimulation
Stimulation is the house stat that controls breeding quality. It is raised by placing specific furniture in your house. Every breeding formula in the game uses Stimulation as its input variable.
How to raise Stimulation: Place furniture with Stimulation bonuses. Prioritize items from the Atomic, Art Deco, and 80s themed furniture sets. Rare variants of furniture provide double the normal stat bonus.
Stat Inheritance Formula
Each of the 7 stats (STR, DEX, CON, INT, SPD, CHA, LCK) is inherited independently. For each stat, the game picks one parent's value. The probability of inheriting the higher parent's stat is:
P(higher) = (1 + 0.01 × Stimulation) / (2 + 0.01 × Stimulation)
Probability Table: Inheriting the Higher Stat
| Stimulation | P(Higher Parent) | P(Lower Parent) | |-------------|-----------------|-----------------| | 0 | 50.0% | 50.0% | | 10 | 52.4% | 47.6% | | 25 | 55.6% | 44.4% | | 50 | 60.0% | 40.0% | | 75 | 63.6% | 36.4% | | 100 | 66.7% | 33.3% | | 150 | 71.4% | 28.6% | | 200 | 75.0% | 25.0% | | 300 | 80.0% | 20.0% | | 500 | 85.7% | 14.3% |
Key insight: The formula asymptotically approaches 100% but never reaches it. Even at Stimulation 500, there is still a 14.3% chance of inheriting the lower parent's stat for each attribute. Breeding perfect cats requires multiple generations, not just high Stimulation.
Practical target: Stimulation 100 (66.7% per stat) is a reasonable mid-game goal. At this level, the probability of all 7 stats inheriting the higher value is 0.667^7 = approximately 6.1%. You will need about 16 breeding attempts on average to get a perfect 7/7 inheritance.
Skill Inheritance
Skills are inherited separately from stats with different formulas.
Active Skill 1 (First Skill Slot)
P(inherit) = 0.20 + 0.025 × Stimulation
| Stimulation | Probability | |-------------|------------| | 0 | 20% | | 16 | 60% | | 32 | 100% (guaranteed) |
Stimulation 32 is the magic number for first skill inheritance. Below 32, you are gambling. At 32+, the first active skill always transfers.
Active Skill 2 (Second Skill Slot)
P(inherit) = 0.02 + 0.005 × Stimulation
| Stimulation | Probability | |-------------|------------| | 0 | 2% | | 50 | 27% | | 100 | 52% | | 150 | 77% | | 196 | 100% (guaranteed) |
Second skill inheritance requires Stimulation 196 for guaranteed transfer. This is a late-game goal — most mid-game breeders will not hit this consistently.
Passive Skill Inheritance
P(inherit) = 0.05 + 0.01 × Stimulation
| Stimulation | Probability | |-------------|------------| | 0 | 5% | | 25 | 30% | | 50 | 55% | | 75 | 80% | | 95 | 100% (guaranteed) |
Stimulation 95 guarantees passive inheritance. This is more achievable than the second active skill threshold and should be a mid-game priority.
Practical Skill Breeding Strategy
- First milestone: Stimulation 32 — Guarantees first active skill transfer. Achievable in early-mid game.
- Second milestone: Stimulation 95 — Guarantees passive skill transfer. Mid-game target.
- Third milestone: Stimulation 196 — Guarantees both active skills transfer. Late-game goal.
Inbreeding: COI (Coefficient of Inbreeding)
Mewgenics uses Wright's Coefficient of Inbreeding formula to track genetic diversity. Breeding closely related cats increases the COI, which increases birth defect probability.
The COI Formula
COI = Σ 0.5^(n-1) × (1 + fA)
Where:
- n = loop length (number of generations in the ancestral path connecting the parents through a common ancestor)
- fA = the common ancestor's own inbreeding coefficient
- The sum is over all common ancestors
What This Means in Practice
| Relationship | Approximate COI | Defect Risk | |-------------|----------------|-------------| | Unrelated (stray cats) | 0.00 | 2% (base rate) | | Half-siblings | ~0.125 | 2% (below threshold) | | Full siblings | ~0.25 | 4% | | Parent-child | ~0.25 | 4% | | Grandparent-grandchild | ~0.125 | 2% | | Double first cousins | ~0.125 | 2% | | Repeated inbreeding (3+ generations) | 0.4+ | 10-42% |
Birth Defect Probability Formula
P(defect) = 0.02 + 0.4 × clamp(COI - 0.2, 0, 1)
Breaking this down:
- Base defect rate: 2% (always present, even with unrelated parents)
- COI ≤ 0.2: No additional risk beyond the 2% base
- COI > 0.2: Risk increases linearly at 40% per unit of COI above 0.2
- Maximum defect rate: 42% (at COI ≥ 1.2, which requires extreme inbreeding)
Safe Breeding Guidelines
- COI below 0.2 is safe. No additional defect risk beyond baseline.
- Stray cats always have COI = 0. Introducing a stray cat into your breeding line resets the inbreeding accumulation for that branch.
- Track relationships within 4 generations. Relationships of 5+ generations apart have minimal COI impact.
- Never breed full siblings more than once in a line. The COI compounds rapidly with repeated close-relative breeding.
Hereditary Disease
Separate from birth defects, hereditary diseases have fixed inheritance rates:
- From mother: 15% chance of inheriting her diseases
- From father: 15% chance of inheriting his diseases
- Not affected by Stimulation — you cannot breed away disease risk
The only mitigation is keeping diseased cats out of your breeding pool entirely.
Body Mutation Mechanics
Physical appearance (body type) uses a different system from stats and skills:
- 80% chance: The kitten inherits the parent's complete body type (all body parts as a set)
- 20% chance: One random body part mutates to a different variant
Body mutations are cosmetic but contribute to the game's trait collection system. If you are breeding for specific appearances:
- At 80% inheritance rate, you will typically see the parent's body type reproduced faithfully
- The 20% mutation rate means roughly 1 in 5 kittens will have one different body part
- Mutations are random — you cannot control which part changes or what it changes to
- The Mutation house stat increases the chance of overnight natural mutations (separate from breeding mutations)
Dominant and Recessive Traits (79+ Traits)
This is where Mewgenics actually uses Mendelian genetics. The game has 79+ visual traits governed by dominant/recessive alleles:
- Dominant traits (represented by uppercase letters): Only one copy needed to express
- Recessive traits (represented by lowercase letters): Both copies must be recessive to express
Each parent contributes one allele per trait. Standard Punnett square logic applies:
- DD or Dd → Dominant phenotype
- dd → Recessive phenotype
This means a cat can carry a recessive trait without showing it, and two dominant-phenotype parents can produce a recessive-phenotype kitten if both are carriers (Dd × Dd → 25% dd).
Putting It All Together: Breeding Optimization
Step 1: Get Stimulation to 32 (minimum)
This guarantees first active skill inheritance and gives you ~57% chance of inheriting the higher stat per attribute.
Step 2: Breed for stats across 3-4 generations
With Stimulation 100, you need ~16 attempts per generation for perfect stat inheritance. Breed the best offspring with outside (unrelated) cats to maintain low COI.
Step 3: Push Stimulation to 95 for passive skills
Once your stat lines are established, focus on transferring the passive skills you want.
Step 4: Endgame — Stimulation 196 for complete skill transfer
At this point, both active skills and passives transfer guaranteed. You are now breeding cats with predetermined stats AND skills.
Step 5: Manage COI by introducing stray cats every 3-4 generations
Stray cats (COI = 0) reset inbreeding risk. Their stats will be random and likely lower, but the genetic diversity they provide prevents the defect rate from spiraling to 42%.
Family Tree Unlock
To view your breeding history in-game, you must donate 21 cats to the NPC Tink (10 + 10 + 1 in three stages). This unlocks the Family Tree viewer, which shows ancestral relationships and helps you track COI visually.
This is a hidden mechanic — the game does not tell you about it. Prioritize unlocking it early because tracking relationships manually is impractical beyond 2-3 generations.