I was just wondering if anyone had any insight on how genetics work in Sims3. I've been testing it out with a bunch of blonde/ginger and blue/purple eyed Sims in the game and keep getting very odd genetics...

At one point I got a girl with brown hair and then a while after that a girl with black hair. I know you can easily change hair color, but that doesn't change genetics (does it?).

Those two odd-ball kids were both from parents with blonde and red hair... so how is that possible?

There is a 10% chance of getting random features in this game...

Changing hair color does seem to change genetics. If mom/dad dies his/her hair green before baby is born there is a chance the baby will have green hair, plus there's always a chance of the 10% random feature alyria mentioned.

Thanks! I didn't know about the 10% but that sounds about right for my neighborhood.

They got rid of Mendelian genetics in Sims 3. Sims don't have hair genetics anymore. They just have a chance of inheriting either parents' current hair color or random. They do NOT have a genetic hair color. Whatever you change it to is what it is, as if that's their new genetic color.

I've had a sim pass down his mother's hair color to one of his children. It's likely it was just a mutation, but purple hair doesn't seem like it would just pop up, especially the same shade of his grandmother's purple hair... but I think that ancestors probably play a role in hair color genetics as well, so it isn't just the parents or random.

It seems to a weighted percentage between parents, grandparents, and random. So sims retain no memory of their parents' characteristics but those characteristics may show up in children. Great-grandparents' characteristics don't figure at all.

Make two sims with the same color hair in CAS, then make a child with them. Keep hitting reload on the kid, you will say WTH!?!?! at least once. There is a 10% chance for random features, it's in the code.

Oh, I know there's random mutations (and honestly, I rather like it), I'm just saying that grandparents' genetics are probably taken into account as well.

Grandparents' genetics aren't taken into account. Grandparents' characteristics are. The difference is, if it were genetics, a new sim could choose from two grandparent genes carried by the parent out of four possible grandparent genes. With characteristics, a new sim can receive any of the four possible grandparent characteristics as the algorithm looks at the family tree not the parent genetics.

Genetics:
Grandparents—[blue/blue BROWN/blue] [BROWN/blue BROWN/blue]
Parents—[blue/blue] [blue/blue]
Child—blue/blue (BROWN not possible)

Characteristics:
Grandparents—[blue BROWN] [BROWN BROWN]
Parents–[blue blue(by mutation, not inheritance)]
Child-blue, BROWN or random

Thanks gotchan for clearing that up. I understand it now, I think.

So if the game looks at family trees and not genetics, does that mean that when an adopted child grows up to have children, their children could end up with the adoptive parents' ( the new child's grandparents on the family tree)'s characteristics?

Seems weird to just have a random hair color. What about two Asian parents having a child? They may end up with a redhead? That's just weird. I prefer the Mendelian genetics of Sims 2.

Oh, and honestly, genetics-wise -- I can't tell anything until they're teenagers. All toddlers look *exactly* the same.

I think everyone does. I'm going to hazard a guess that they got rid of Mendelian genetics in order to keep loading times fast and to avoid the mess of accumulating SimDNA files when a sim is deleted (or moves away - same as being deleted, an integral part of story progression). Now when sim deletion occurs, every reference to that sim can be cleanly removed from the neighborhood file as if they never existed. I think it's the same reason they no longer have memories. The DNA and memories really complicated Sims 2 saved neighborhoods and made it nearly impossible to completely and cleanly remove a sim.

Personally, I think a well-designed relational database could have allowed keeping Mendelian genetics and memories, but what do I know.

Here's a genetics issue I have heard about, but I am not sure if it is true.

I've heard that if you go into CAS and roll a random sim with black hair, then change his hair to blond, then he can pass on either blond or black hair to his children.

I bet that's right, based on how dying a Sim's hair works, but I wonder if anyone has proof of it.

I don't think that's what happened. I think the sim was passing on blonde hair but the kid hit the 10% random thing and ended up with black hair and that's how the player explained where the black hair came from. The game doesn't remember hair colors anymore.

That seems strange. I'm not doubting you at all, but it sure seems a bizarre way to implement the feature.

I would've thought they would just have the SimDNA attached to the individual. When you delete the sim, you delete the DNA as well. Since the game already tracks family trees, it would be a simple matter to just trace back up the tree until DNA is no longer found, and simply stop the search for genes there. This does mean that certain genetics will mysteriously disappear in a single generation on the worst-case scenario, but I still doubt it would be that noticeable. After all, any children will have their own complete genome that would've had to have inherited at least somewhat from their parents, even if said parents move away/die/are deleted.

It seems like it should be a non-issue if you just keep DNA data with current, existing Sims (since ghosts would have SDNA too, it appears).

The reason EA got rid of Mendelian genetics was because we can now choose literally any color our computers can display for hair and eyes, and I guess they didn't want to have to label every single possible color value (There's 18,821,096 of them) as either recessive or dominant.

Although, if it's possible to radically modify how the game does genetics, someone could give expression priorities to bands of the RGB channels* (how the game stores what color your sims' hair is) to make hair/eye genetics similar to what we had in Sims 2. It would take a ton of tuning to get all of the color bands right, and that's completely ignoring the huge modifications to how the game handles and saves genetics.

*For example: 55-91.50-62.0-37 (r-r.g-g.b-b) would be a brown/dominant band of the color spectrum.

It is, and your suggestion is workable. They just didn't do it that way. Personally, I'd give each sim a genome string. It wouldn't effect play as it is only referenced when creating born in game sims, but you could get some wonderfully subtle effects from it.


That's an interesting question. The answer depends on whether adopted children replace any earlier family tree with the adoptive family tree, keep the old family tree, or blend the family tree. I don't know, but I can't resist guessing. Given the brutally simple approach the programmers took to most problems, I'd guess they didn't choose blending trees. Given that the UI depends on current relationships, I'd guess any previous family trees get thrown out. Therefore, I'd guess adopted kids inherit characteristics from adoptive parents and grandparents. They same applies to stepchildren and stepparents.

Edited to add:

That's an extremely simplistic way of approaching the problem, which is a reflection on them, not you. For instance:
They could have defined 26 genetic hair colours, A through Z.
Each of those genetic colours represents a range of RGB values.
The root colour set in CAS is genetic and cannot be changed once CAS is left.
Root colours set in CAS are assigned a genetic value based on what range the RGB value falls in.
Genetic values from breeding are expressed as root colours based on the key RGB value and a random adjustment within the range. Sims with the same genetic hair colour value will have different colour hair within the RGB range represented by that genetic value.
Elder's roots are expressed as grey but maintain their original genetic value.
Dominance is a simple A dominates B dominates C et cetera.
To keep one colour from dominating over time, visually similar colours can be mixed up in the A-Z ranges. (i.e. A=black1, B=brunette1, C=blonde1, D=redhead1, E=brunette2, F=blonde2, G=redhead2, H=black2, and so on.)
Each sim gets two hair codes. Using the above mapping, sim one with AF would have hair roots in the black1 range. Sim two with FH would have hair roots in the blonde2 range.
Children would randomly receive one of two hair codes from parent one and one of two from parent two.

Since a sims genetic code is translated to RGB values via table, the game can allow players to customize the table to have custom dominance values in their games. Player one maps A to a dark brown range. Player two maps A to a light purple range. Some players might map all value A-Z to the same RGB range. This additional functionality would require the creation by the game of custom colour wheels in CAS as some players might choose to not use the full range of hair colour allowed by RGB colour space. None of this is difficult. It just requires careful planning. (Simple and easy are not the same thing. Neither are complex and difficult.)

Yup, I liked the Mendelian genetics too.

I'll just pretend that the sims world falls under the law of Anime.

This is only loosely related, but I have a genetics-related gripe.

With the skin color sliders EAxis put in place for TS3, I was hoping that skin color would be more real-world reflective; my self-sim and boyfriend-sim can not have realistic looking children (I'm white, he's black.) They have to be created in CAS to have the right skin color... Babies that we give birth to all have either his skin (believable, but disappointing) or mine (highly unlikely.)

I understand that the way the skins worked in TS2 made it impossible, but why is it still like this? Am I the only person irritated by it? I never see anyone else reference it...

It's the same reason as the hair. Skin colour is a simple characteristic. The game scans the family tree and selects a skin colour represented there at random or generates a fresh one at random. Skin colours from the same CAS slider may be blendable for born-in-game sims, but there is very little evidence. Skin colours from different CAS slider are not blendable for born-in-game sims, even if they are both light to dark sliders.

No information is stored about skin colour or hair colour other than in the model texture. If a sim changes his or her hair or skin colour, then his or her heritable hair or skin colour also changes. Lamarckian hair dyes and tanning beds.

Twice now that's occured in my game, and the offspring has been born with a pleasant blend of both parents' skintone - one of them a fraternal twin, amusingly enough. .

That's encouraging, but it doesn't happen very often.