Breeding is the production of offspring. In Crusader Kings III, this also includes intentional strategies that aim to increase the likelihood of passing down certain congenital traits. This often involves marrying characters with any of the desired traits, and purposely disinheriting heirs that did not inherit the desired trait(s).
Trait inheritance
Congenital traits
Congenital, or genetic, traits can be inherited by a character's offspring. Although genetic traits must be visible to provide stat bonuses and other effects, a character may also carry recessive traits which are invisible, yet can be inherited by one's children.[1]
Active
First the chances of acquiring the trait as an active trait is checked as a function of the parents:[2]
Mother Father
|
None | Inactive | Active |
|---|---|---|---|
| None | 0% | 2% | 25% |
| Inactive | 2% | 10% | 50% |
| Active | 25% | 50% | 80% |
Inactive
If that check fails the chances of inheriting inactively is calculated:[2]
Mother Father
|
None | Inactive | Active |
|---|---|---|---|
| None | 0% | 25% | 75% |
| Inactive | 25% | 50% | 100% |
| Active | 75% | 100% | 150% |
General logic for trait with tiers inheritance
- Start from highest trait
- Calculate active chance. Lower tiers ( including inactive ) count as inactive of the tier. Each level down beyond the first multiplies chance by a define
- If active, use it; DONE
- Otherwise, go down a tier, if inactive pretend 1 more parent has that tier active, otherwise 1 more parent has it inactive.GOTO 2
When trying to inherit a tiered genetic trait, and the other person has one of lower tier, we pretend that means they've got the higher tier one recessively, and reduce the chance of inheritance by 20% per tier further down than 1 the other parent's trait is.
When going down a tier, add 40%.[2]
List of congenital traits
The table below contains all genetic traits that use the inheritance mechanism as described above.[3][4] This list does not contain traits such as 
Sayyid, which can be inherited from a character's non-biological parent (in the case of secret bastards), or 
Inbred which uses a custom inheritance chance. The natural prevalence column denotes the likelihood of any character being born with the trait if it is not inherited from their parents. For every trait with natural prevalence, the same value can be assumed for random prevalence (i.e. for generated characters).[3] Note that some traits cannot be inherited at the same time since they are incompatible; such traits are indicated if they belong in the same group.
| Trait | Natural prevalence (%) | Group | Notes |
|---|---|---|---|
 Melancholic (genetic variant)
|
0.5 | - | If inherited on birth, it is initially hidden.[5] |
 Lunatic (genetic variant)
|
0.5 | - | 如果在出生时被遗传，最开始将是隐藏（未激活）的。 |
 Possessed (genetic variant)
|
0.5 | - | 如果在出生时被遗传，最开始将是隐藏（未激活）的。 |
 Homely
|
0.5 | Beauty | |
 Ugly
|
0.25 | Beauty | |
 Hideous
|
0.15 | Beauty | |
 Comely
|
0.5 | Beauty | |
 Pretty / Handsome
|
0.25 | Beauty | |
 Beautiful
|
0.15 | Beauty | |
 Slow
|
0.5 | Intelligence | |
 Stupid
|
0.25 | Intelligence | |
 Imbecile
|
0.05 | Intelligence | |
 Quick
|
0.5 | Intelligence | |
 Intelligent
|
0.25 | Intelligence | |
 Genius
|
0.05 | Intelligence | |
 Delicate
|
0.5 | Physique | |
 Frail
|
0.25 | Physique | |
 Feeble
|
0.15 | Physique | |
 Hale
|
0.5 | Physique | |
 Robust
|
0.25 | Physique | |
 Amazonian / Herculean
|
0.15 | Physique | |
 Fecund
|
0 at birth[6], unknown for generation | Fertility | |
 Club-footed
|
0.5 | - | 也可以通过近亲繁殖获得。 |
 Hunchbacked
|
0.5 | - | 也可以通过近亲繁殖获得。 |
 Lisping
|
0.5 | - | |
 Stuttering
|
0.5 | - | |
 Dwarf
|
0.5 | Stature | 也可以通过近亲繁殖获得。 |
 Giant
|
0.5 | Stature | 也可以通过近亲繁殖获得。 |
 Spindly
|
0.5 | Physique (incompatible with good traits) | 也可以通过近亲繁殖获得。 |
 Scaly
|
0.5 | - | 也可以通过近亲繁殖获得。 |
 Albino
|
0.5 | - | |
 Wheezing
|
0.5 | - | 也可以通过近亲繁殖获得。 |
 Bleeder
|
0.5 | - | 也可以通过近亲繁殖获得。 |
 Barren / Sterile
|
0.5 | Fertility | Also gained via inbreeding. |
List of other inherited traits
The following list contains all other traits that use a separate inheritance mechanic. For entries without a chance to inherit value for both parents, assume the value for single parent.
| Trait | Chance to inherit (%) | Notes | |
|---|---|---|---|
| Single parent | Both parents | ||
 Great Pox
|
10 | - | |
 Lover's Pox
|
10 | - | |
 Pure-blooded
|
15 | 75 | Gained initially through inbreeding. |
| Inbred
|
15 | - | Gained initially through inbreeding. |
| Sayyid
|
100 | - | Only inherited from apparent father. |
 Saoshyant /  Saoshyant Descendant
|
100 | - | When parent has Saoshyant, Saoshyant Descendant is inherited instead.[7]
|
 Paragon /  Consecrated Blood
|
100 | - | When parent has Paragon, Consecrated Blood is inherited instead.
|
| The Savior / Divine Blood
|
100 | - | When parent has The Savior, Divine Blood is inherited instead.
|
Inbreeding
Inbreeding is the process of two related characters having children together. For these purposes, related characters are those who share a common ancestor. Such children can be born with negative congenital traits even if neither parent has them. However, there is a small chance for the child to gain the 
Pure-blooded trait instead. The chance to gain inbreeding traits is low in the first generation, but each successive generation has a higher chance. Related characters are also harder to use the Seduction Scheme on unless either the target character's Faith accepts it or if the seducer has the Subtle Desire perk.
Common ancestors
The more common ancestors two parents have within four generations (up to their great-great grandparents, and including themselves), the more likely their children will be inbred.[8] Some potential incestuous marriages are noted below. The value provided for common ancestors assumes that ancestors were otherwise non-incestuous and monogamous. Cousins are not removed. Additionally, the value is relative to the breeding couple.
| Relation | Common ancestors | Explanation |
|---|---|---|
| Full siblings | 30 (maximum possible) | By definition, (full) siblings share parents, and thus by extension all other ancestors. The maximum amount of ancestors from n generations can be found from [math]\displaystyle{ \text{Max Ancestors} = 2 ^ {n + 1} - 2 }[/math], thus being 30 from 4 generations. Or, written out, full siblings share both parents (2), two sets of grandparents (4), four sets of great grandparents (8) and eight sets of great-great grandparents (16). |
| Parent-child | 15 | In the case of a partner being the other partner's ancestor, they are counted as a common ancestor.[9] As a result, the common ancestors are the following (perspective is child/parent): parent/self (1), one set of grandparents/both parents (2), two sets of great-grandparents/standard grandparents (4), four sets of great-great grandparents/great grandparents (8). Note that the parent's great-great grandparents are the child's 3×-great grandparents, and are therefore not counted. |
| Half siblings | 15 | They share one parent, and therefore share only half of the maximum amount of ancestors. Alternatively, they share one parent (1), one set of grandparents (2), two sets of great grandparents (4) and four sets of great-great grandparents (8). |
| First cousins | 14 | First cousins share grandparents (2), two sets of great grandparents (4) and four sets of great-great grandparents (8). |
| Uncle-niece/aunt-nephew | 14 | Similar to first cousins, but rather than sharing grandparents, the nibling's grandparents are the uncle/aunt's parents. Note that since the uncle/aunt's great-great grandparents are the nibling's 3×-great grandparents, who are 5 generations away from the nibling's perspective, they are not counted. |
| Second cousins | 6 | Second cousins share one set of great grandparents (2) and two sets of great-great grandparents (4). |
| Third cousins | 2 | Third cousins share one set of great-great grandparents. |
Chance of inbreeding
The chance of a child being considered inbred can be found from the product of the following:[10]
- Number of common ancestors
- Inbreeding factor based on number of common ancestors
- Inbreeding chance modifier. Currently, only the Pure-blooded trait provides such an effect.
Inbreeding factor
The inbreeding factor for a given amount of common ancestors can be found through the following:[2]
| Common ancestors | Factor | Chance before modifiers |
|---|---|---|
| 0-14 | 0.33 | Between 0% and 4.62% |
| 15-16 | 0.75 | Between 11.25% and 12% |
| 17-19 | 1 | Between 17% and 19% |
| 20-21 | 2 | Between 40% and 42% |
| 22-30 | 3 | Between 66% and 90% |
Chance of gaining the Pure-blooded trait
The Pure-blooded trait may be inherited from one's parents. Otherwise, it may be gained naturally. Similar to the chance of inbreeding, the chance of gaining the Pure-blooded trait naturally is based on the number of common ancestors, multiplied by the corresponding level factor for that amount of common ancestors:[2]
| Common ancestors | Factor | Final chance |
|---|---|---|
| 0-19 | 0 | 0% |
| 20-21 | 0.15 | Between 3% and 3.15% |
| 22-30 | 0.3 | Between 6.6% and 9% |
As a result, parents must have at least 20 common ancestors for a child to gain the Pure-blooded trait naturally. This does not apply to inheriting it from parents.
Traits gained from inbreeding
The following traits may be gained from inbreeding. With the exception of Inbred and Pure-blooded, traits seem as though they appear equally likely.[5]
| Trait | Notes |
|---|---|
| Barren / Sterile
|
|
| Scaly
|
|
| Club-footed
|
|
| Wheezing
|
|
| Spindly
|
|
| Giant
|
|
| Hunchbacked
|
|
| Bleeder
|
|
| Dwarf
|
|
| Pure-blooded
|
Chance is based on amount of common ancestors. |
| Inbred
|
Exact mechanic unknown. However, the following has been observed:[5]
|
Effect of Pure-blooded on inbreeding
The Pure-blooded trait provides −50% chance of inbreeding per parent. If two parents have the Pure-blooded trait, this effect combines to no chance of gaining traits due to inbreeding. Note that this excepts the chance of gaining the Pure-blooded trait naturally, as well as the inheritance of such traits via parents. It is unknown whether the Pure-blooded trait has an effect on gaining the Inbred trait.[5]
See also
References
- ↑ "[Genetic traits are] visible, though characters can also carry recessive traits... those are not visible, but can be inherited by their offspring!" rageair's reply in CK3 Dev Diary #7 - Characters & Portraits thread
- ↑ 2.0 2.1 2.2 2.3 2.4
common\defines\00_defines.txt,NChildbirth - ↑ 3.0 3.1
common\traits\00_traits.txt - ↑ "[If genetic = yes, the trait's] inheritance will follow the following rules: The trait can be inactive. Children can inherit the trait from both active and inactive parent traits. [...] An active trait is inherited with 100% chance, an inactive trait with a 50% chance. If the trait is successfully inherited from both parents, it becomes active. [...] If it's inherited only from one parent, it's inactive." Developer comments in
common\traits\_traits.info - ↑ 5.0 5.1 5.2 5.3 Pure-blooded effect on inbreeding on talk page
- ↑ Natural prevalence of Fecund on talk page
- ↑
events\decisions_events\major_decisions_events.txt,major_decisions.0101 - ↑
game\common\defines\00_defines.txt,NChildbirth|INBREEDING_ANCESTOR_GENERATIONS = 4 - ↑ The fact that the parents themselves are included in the common ancestor count is implied in the wording of developer comments found at
game\common\defines\00_defines.txt(emphasis added): "How many generations are checked for common ancestors of the both parents (including the parents) for the purposes of getting the inbreeding trait and the pure-blooded trait" - ↑ "The final chance [for inbreeding] in percent is given by the number of common ancestors X corresponding level factor X inbreeding chance modifier" Developer comments in
game\common\defines\00_defines.txt.