My sister plays an Ex Miscellanea magus who met a young (Gifted) shepherd ; she is by now both his wife and apprentice.
My sister would like to see them have some Gifted children. But I only have a few clues about the interaction between bloodlines and Gift inheritance.
What I imagined was something like this :
-Does the father have the Gift ?
-Does the mother have the Gift ?
-Does the future mother pass her pregnancy in a supernatural aura/regio of about 3+ ; or is she affected by some enchantment or magical permanent during her pregnancy ?
For any previous "yes" answer, I give you a Tense dice. Should you roll one (or more) "1" you get the Gift. It may be Blatant or Subtle though. I guess that don't have to be correlated to the previous answers (or only partially).
I wonder if someone tried to rule that and how ?
What about running your sister's magus through a few adventures concerned with AM p.54ff Fertility Magic? It looks like he has a knack for the countryside, so finding p.59ff Cave Systems and exploring them should be possible.
Your sister might appreciate both the Arcane Ability Fertility Lore (p.55, only 15 Breakthough points) and the Minor Hermetic Virtue Fertility Ritual Magic (p.55, 35 Breakthrough points).
Of course, just hoping that a child be Gifted works as well, ... if the SG is sympathetic. But just what kind of Gift this might be? After all, many parents wish to get rid of Gifted children asap.
I don't remember the source but there's about 1 gifted person for each 10.000 habitants.
So there's those two male players playing a male and a female maga and they agreed they wanted they chars to produce a gifted baby.
All I can say was... "Ok, so you both can... roleplay you are enganging in intercurse with the goal do get the female char pregnant. Alright?"
I will not describe the session but was actually a bit embarrasing for both players.
A female can try to get pregnant once a month a male can try each night (with a different female).
Each player will make a stamina roll.
The sum fo the couple stamina roll must be 12+ (really easy).
Each parent must roll a dice. A botch means there's no baby this month (make male players botches particulary embarassing).
A month after intercourse a spontaneous intellego corpus 10+ can tell if the female is pregnant.
Ok, now we have a pregnant female but we are in medieval times.
Each season the female should make an aging roll. A botch means she lost his baby (cruel I know) and all other rules for aging apply.
After 3 successfull rolls we got a beautifull baby.
Now we can determine if the baby will be gifted but first we can throw a coin or make 5 nasty (-5 to -1 stamina rolls) aging rolls.
It's medieval times and the infant mortality rates are high 30% maybe 50%.
Also as a rule of tumb there's no gift signal before 5 meaning there's a big investment in parenting BEFORE you actually knows how the infant will develop.
Each parent roll a dice, a non gifted parent must roll 1 twice and a gifted parent must roll just a single 1.
That means each pair of grogs get a 1/10.000 chance and a pair of magi get 1/100 chance (still very slim).
Gender is not determined because if a player decides to actually play that kid as a PC the players can decide it's apparence. Otherwise flip a coin.
Such low probality of a gifted baby can be a nice hook for a saga. Maybe a very powerfull faerie or demon will propose a deal only to kidnap the infant at young age.
Sub Rosa 11 have an article about conception and pregnancy and they gave an 6% chance that you get a gifted child what might already a to big chance (or not given that many gifted children probably not survive the first years)
Canonically there is at least one House that asserts all of their Gifted members are descended from their Founder: Mercere. It's possible that they are no more numerous than other bloodlines, or that descent from Mercere is a special circumstance.
Magi wishing to produce Gifted children may well throw the kitchen sink at it; two Gifted parents, fertility magic, auspicious horoscopy, deep Regio, and anything else they can think of.
No special circumstances - but that House carefully tracks and encourages a big bloodline, with very few Gifted examples resulting (see HoH:TL p.94f Magical Merceres). So they still take Gifted outside apprentices, which they label Illegitimate (HoH:TL p.94 and p.109 Illegitimate Lineage). And I am sure, that so far they have not yet discovered AM p.54ff Fertility Magic - though I expect lots of sagas to change that as they proceed. 8)
They take descendants of Mercere whose specific descent is not known: blood relationship can be established with Intelligo magics.
We know there is a substantial portion of Recaps who are descended from Mercere, but I don't know of numbers. If half of House Mercere (about 75 members) is descended from the Founder, the twelve Magi Mercere represent about 12% of the extended family. If two-thirds of the House are descendants, about 24%. If one-third, about 4%. If all of the House is descended from Mercere (which almost certainly they are not), about 8%.
How many is 'very few' is subjective, but 8%-24%, averaging 16% seems a high proportion to me.
So, descent from Mercere seems to have some evidence of increased likelihood of the Gift.
Of course it may simply be that Mercere was descended from some earlier proto-founder who is also the ancestor of all Gifted, and the strain in his bloodline is slightly more common, but this is strictly speculation.
I suspect having children in the first place - Magi Mercere do, and other magi tend not to, is also an important factor.
Indeed - and we know that a particular magical aptitude (Mutantum) is linked to the Mercere bloodline. And Mercere himself had two Gifted sons.
There's no indication that this applies to the Gift in general, though (though it might for Mythic Blood) - but of course, that doesn't mean you can't throw the kitchen sink at an attempt to have a Gifted child.
As a general rule, descendants of Gifted folk are more likely to be possess The Gift than the general population, but it's never been made clear to what extent this is the case save in the case of one Rhine magus (GotF page 59) who only has Gifted children (his semen constitutes a vis source). This is suggested to be extremely rare!
Well, yeah - Petrus Virilis is a walking story seed, if you'll pardon the stealth pun. Same with any other means of reliably ensuring Gifted babies. (Fertility Magic in particular would cause an earthquake in the current dynamics of the Order, not to mention royally pissing off the current Bonisagus leadership.)
What is also important is that a magus or even an bloodline know what it really means to have a child that show signs of the gift while other parent might even try to kill a child that show the downsides of the gift or god beware a turbulence (this child must be possessed by a devil).
Note, that not all the descendents of Mercere in 1220 are in the House.
Mercere died 818 AD (HoH:TL p.144). HoH:TL p.78ff House Mercere describes its state around 1220 - so 400 years later: 12 Gifted Mercere. Over these 4 centuries - some 20 medieval generations of 20 years - the House has encouraged and supported procreation (HoH:TL p.94f), cared for its biological descendents and screened them for the Gift. If we assume 2 Mercere Magi in 1220 to be of HoH:TL p.109 Illegitimate Lineage, this means that of the thousand or more known descendants of Mercere in 1220 only 10 were found Gifted: at the very best 1%. [Note, that disregarding effects of implex (relevant because of high number of generations) and population increase (quite relevant), the blood of Mercere, however thin, after 20 generations would run in about 2 to the power of 20, that is over a million, people: no real chance to keep track of them all, or check them for the Gift.]*
Still a little better than the 0.01% bulinckx recalls, or the value Mark Shirley computes in sub rosa #14 p.28 Supply of Apprentices and Prevalence of The Gift as the absolute minimum for the Order to exist as it is in 1220: one Gifted birth per 49,000 people in every seven years.
EDIT: I quoted a trivial miscalculation from sub rosa #14 p.28 Supply of Apprentices and Prevalence of The Gift, which I now have corrected. And I added some simple math here:*
The less-magical descendants of Mercere have, of course, been weeded out of the lineage, leading to rare occasional throwbacks, whose descent from Mercere has become clouded. Intelligo magic can establish relation to common ancestors; the illegitimate Magi Mercere are of unknown relation to Mercere, not non-relation to Mercere.
Parentage is one of the factors of the Gift. It is not required, it is not exclusive, it is not universal, but it is a factor.
For the magus wishing to produce Gifted children, I suggest throwing as many factors at it as possible, and not getting your hopes up too much.
That 0.01% is for random non gifted parents and 1% for (both) gifted ones. You can think it in modern genetics as a recessive gene manifests only 10%.
That's why each parent must roll a 1 in 1d10 even if they are gifted.
Also note there are population estimatives for 1220 Europe in the range 8 millions and there are less than 800 wizards in the order at this time*
*I gpt those values form the top of my head from something I read many years ago. Please correct me with the new resources.
By no longer keeping track of that person's lineage; after no magical presentation, the line is eventually no longer tracked, or ignored, or forgotten. The descendant wanders off from the family, or is expelled, or otherwise in some fashion no longer tracked. Of course, there are by-blows the House is never aware of.
(Why Mercere would care about illegitimacy, when they can establish correct descent, is a mystery to me; it isn't sexual mores. The Mercere have idiosyncratic sexual mores.)
Intelligo Corpus, Base 5: Sense a specific piece of information about a body, in this case, degree of relationship. I can speculate that a few devices with this effect have been created, or perhaps not. In any case, the application of the effect lets a breeding program avoid consanguinity.
Please read my full post again: I didn't misread you, but compared numbers for Mercere's offspring with numbers you recalled for random non gifted parents.
The best current treatment I know of is Mark Shirley's Demography of the Order of Hermes in sub rosa #14 p.24-33: 1222 there are some 1267 Hermetic magi out of a population of Mythic Europe of a little under 70 millions. But a lot of other traditions compete for Gifted children, too - and many Gifted children may end up undiscovered, neglected, despised or even killed.
The OP may find the Optional Rules for Breeding from Hermetic Projects, p. 140-142. helpful. Those are for breeding animals, and humans are not animals in Mythic Europe; some adaptation may be needed. I've never used them; I don't know how functional they are.