I can't seem to find any information on this topic, so I thought I'd post it here.
Does anyone know how genetics work in The Sims 3?
I know in that in The Sims 2, they had recessive and dominant traits. I was wondering if it's a similar situation in The Sims 3, or if everything is determined randomly.
I would really appreciate an answer to this question!

As I recall, this one truly is a step backward. It's just a mix of the current condition of the two sims. So if one sim dyes their hair purple just before the conception, there is purple genetics in the mix!

Since you can customize the color of EVERYTHING, genetics basically flew out the window with eye/hair color. It picks between the two parents at random.

Which, is kinda how it works anyway. The only loss is dominant/recessive, which isnt that big of a deal. Plus if you get a kid with blonde hair when one parent has pitch black and think it's a bit silly, you can just change it yourself.

So then how do skintones work? Are babies limited to having either one of their parents' skintones or can they be a random shade in between their parents like The Sims 2?

It's not totally random, and you can get traits from grandparents. There's also about a 10% chance of 'Mutations' which are highly annoying. Yellow eyes, and red hair are part of this.. you can have two 'Asian' sims who had 'Asian' parents, and so on, and still get a random redhead or odd eye color once in a while.

There's a mod at MATY that lowers the mutation chances, but I've still seen it happen annoyingly. And as far as skin tone goes it randomly selects the skin of one of the parents, unless you have awesomemod's better genetic skin blending feature enabled. Then the game will pick of of the skintones of the two parents, and pick a shade in between the intensity of the two.

All the sims I've had making babies have been blue sims with random "townies", but they all have seemed to exactly match the skintone of one of the parents.

But are you using awesomemod with better genetic skin blending? Unless you are, that feature does not exist in the game.

Ok, thanks.
I think I'll have to get awesomemod....

<Current_Tuning>
<kSkinColorMaxPercentTravel value="50">
<!--When choosing skin color, max pct change in parent skin tone. Valid range [0, 100].-->
</kSkinColorMaxPercentTravel>
<kInheritGrandparentTrait value="25">
<!--Chance to inherit traits from grandparent. Valid range [0, 100].-->
</kInheritGrandparentTrait>
<kInheritParentTrait value="40">
<!--Chance to inherit traits from parent. Valid range [0, 100].-->
</kInheritParentTrait>
<kInheritBodyShapeShiftAmount value="0.2">
<!--Max amount to shift around inherited bodyshape. Valid range [0, 1].-->
</kInheritBodyShapeShiftAmount>
<kMutateHairColorChance value="10">
<!--Chance for mutation when inheriting hair color. Valid range [0, 100].-->
</kMutateHairColorChance>
<kHairColorChooseGrandparentChance value="50">
<!--When choosing hair color, chance of selecting a grandparent. Valid range [0, 100].-->
</kHairColorChooseGrandparentChance>
<kMutateEyeColorChance value="10">
<!--Chance for mutation when inheriting eye color. Valid range [0, 100].-->
</kMutateEyeColorChance>
<kEyeColorChooseGrandparentChance value="50">
<!--When choosing eye color, chance of selecting a grandparent. Valid range [0, 100].-->
</kEyeColorChooseGrandparentChance>
</Current_Tuning>

The above is from the Genetics XML; this is the entirety of the genetics system, pretty lame if you ask me. Notice at the top on skin color, ONE parent is chosen and child's skin color can be moved up to 50% from the one parent. Really an absurd way of doing it.

This is false. What ACTUALLY happens is that it can be moved up to 50% of the RANGE between the two. This is an apparently purposelessly convoluted way of saying that the result is the evenly-distributed range between the two. How it works:
1. The RANGE between the skin tone levels is computed, MAX-MIN.
2. Flip coin, HEADS: Skin Tone is either MIN + (RANDOM% * MAXTRAVEL* RANGE), TAILS: Skin Tone is MAX - (RANDOM% * MAXTRAVEL * RANGE).
3. ???
4. PROFIT!

As you can see, based on the default max travel%, the result is that essentially a random number picked between the two skin tone levels, meaning. If this tuning value were changed, interesting things would occur: If travel percentage is increased above 50%, then the system will bias towards the center, as the random flip to determine whether we add from min or subtract from max will result in an overlapping range in the middle. For instance, at 60%, there is a a 33% chance of getting a value from +/-10% of the median (2 * 0.5 * (0.2/0.6)), as opposed to 20% for the default (2 * 0.5 * (0.1/0.5)). If the travel percentage set to less than 50%, the perfectly intermediate tones become impossible until it becomes a completely binary decision at 0%. If the travel percentage is set to 100%, the same thing occurs as if it were 50%. If travel percentage is greater than 100%, sims can end up darker or lighter than either input parent, and your sims can therefore spontaneously begin to evolve darker or lighter skin. If the value is < 0%, then your sims will ALWAYS end up darker or lighter than one parent, never an intermediate value.

The Mutation values for eye color are also interesting, because I've calculated the average time to complete extinguishment of all user-introduced genetics in a closed breeding system. Hair color is irrelevant because changes applied in the mirror become "genetic" and are passed down, whereas eye color is immutable within normal gameplay rules. The basic calculations, IIRC, showed that within 10 generations of closed breeding assuming all-original genetics as a seed material, practically all user-introduced genetics will be extirpated, and this will happen even faster if you breed with townies (100% EA genetics).

Head go boom. How does the range work if the parents are from two different sliders? Does the game arbitrarily select one of the two sliders, and then calculate range as if both parents were on that slider? Or is that range simply 0, so the offspring inherits one matching skintone?

Without AwesomeMod? You get one or the other, with no blending or variation. Very jarring if you've picked two "normal" skins. With AwesomeMod? Chooses the more intense swatch, range works as above.

Did anyone ever fix the bug that sims don't get their genetics set at birth? (ie the hair dye becomes genetic)

That isn't a bug, that's a direct outcome of how the game handles hair "color". Since the game does not contrain you to setting "real" genetic hair colors seperately from discolored hair, there is no way for the game to know what is what. In TS2, for instance, sims could not be created using non-binned hair in CAS, you had to set the REAL color first, then change it with a mirror in-game, and the original genetic imprint would be retained. In TS3, genetic haircolor no longer exists.

If it's not a bug, it's a huge design flaw. Assuming the game even pretends to represent human life, it is extremely normal for adult women of childbearing age to colour and highlight their hair, while it is extremely abnormal for their babies to sport the same hair dye.

No, it is NOT extremely normal, it is a revolting habit that smells terrible and looks ridiculous, like you have some kind of weird mange.

Not if you do it right. :P

I take it you never experimented with bleach as a teen.

I'm quite sure you're mistaken. You wouldn't know this because you've played base game for about 10 minutes when the game came out in June. Then you started modding it. WA comes out, you've played it for about 10 minutes with base game EA rules, then you modded it. Simple observation playing base game rules for many months tells me it works the way it's stated in the XML.

It's happened a number of times in my games that a pair of sims are moved into my hood by the immigration who are darkskinned, from Africa they appear to be. Later on these two have a child who is medium-skinned, as if they are from Mexico, South America, wherever. How is it that this much lighter skinned child than both parents is in a "RANGE" between the two parents' skin tones as you state? It just isn't so.

I've also seen a few times two lily-light-skinned Northern Europe parents produce a child who is medium skin color, much darker skin than both parents. A child like this is not a mix of a range between the two parents, the child is way outside the available range as you have defined it. Ergo, your definition isn't right.

Pfft, I don't care about the mechanics, Sim3 Genetics work pretty well for me:



My self-Sim's Great-Grandson, I think he looks rather handsome

heehee, that's funny

Even with AM genetics in the game is funny. My interracial couples of late have always had one child that is black and one that is white. Granted this can happen in real life it's just so weird to see Child A with brown/black hair and green/hazel eyes and the other one with blonde hair and blue eyes. It never fails.

LOL. I was thinking that same thing as I scrolled down the picture and then I saw your note at the bottom. Handsome sim.

No, more like "Steve Holt!".

I am quite sure that there is some amount of blending of traits. For example, these screenshots are from the "Dilute the ugly gene challenge". Look at the hair color.



Dad = Green hair
Mom = Brown hair



A better picture



The daughter's hair is neither green nor brown, but this ugly puke-colored greenbrown.

With more screenshots it'd be easier to tell the difference but since then my game was destroyed and I had to delete this save file, so I apologize for those are the only screenshots I have.