The Ultimate Sims Genetics Tutorial! Chapter 2
This is where you want to begin if you recall the basics of genetics, but still want to know how that translates to the game.
How Genetics Works in The Sims 2
What gets passed from parent to child in the game?
There are four different categories that are heritable in the game: hair, eyes, skintone, and facial traits (such as nose, chin, eyeshape).
Facial Traits
Facial Traits deserve a quick note because they actually follow the simple dominance/recessiveness rules we talked about in the previous chapter. So you often see the same traits popping up over and over again in the same family. The one small exception is when both parents have, say, a dominant nose. In The Sims 2, when there are two dominant alleles, it's a 50/50 chance which allele actually appears on the face of the offspring.
For a quick example of facial traits passing on, check the family tree for the Laurince legacy. Note the prominant nose that is passed on from the Gen 1 spouse to Gen 5 offspring, as well as the chin of the founder that still exists in Gen 7.
Hair
I'd like to talk about hair next, because it's the next simple. There are four hair color bins (excluding, for the moment, the custom bin): Black, Brown, Red, and Blonde.
Black and Brown are both dominant alleles. If an offspring inherits either one of these alleles, plus one for another hair color, they will still express their dominant allele.
Red and Blonde are both recessive alleles. They will not be expressed if there is an allele for black or brown also.
For alleles that are equally dominant, there is a 50/50 chance which trait is expressed. So, if an offspring inherits one Black allele and one Brown allele, there is a 50% chance they will have Black hair and a 50% change for Brown. An offspring with one Red allele and one Blonde allele has a 50% chance for Red hair and a 50% chance for Blonde.
This makes inheritance a little more complicated and a bit more interesting. Now, if you only gave your sims black and red hair, for instance, everything would behave like our tongue-rolling example in chapter 1.
Example: Parent with Black hair and an allele for Red hair (Bk r) x Parent with Red hair (r r)
Okay, that's easy enough. But the outcome gets a little more complicated to predict if you take a parent with an allele for each (Bk r) and cross them with a parent with Blonde hair (bl bl):
You can see how just making one or two genes equally dominant changes the amount of variety you can possibly get. And having people roaming around who are carriers is even more exciting!
Eyes
There are five Maxis eye colors: Brown, Dark Blue, Light Blue, Green and Gray. The way genetics works with eye colors is very similar to hair inheritance.
Dominant Eye Alleles: Brown and Dark Blue
Recessive Eye Alleles: Light Blue, Green, and Gray
Again, eye colors on the same level of dominance have a 50/50 chance of being expressed, if offspring inherits two different alleles from their parents.
Skintones
Skintones are determined entirely differently from the other categories. It's both simpler and more complicated, if that's possible.
You see, instead of having dominant and recessive alleles, Sims' skintones are on a spectrum from light to dark. There are four default skintones, which are often referred to as S1 (light), S2 (tan), S3 (medium), and S4 (dark).
An offspring's skintone is determined like this: a child can have any skintone between that of its parents, including the skintones of the parents. Each skintone in the possible range has an equal chance of being inherited. So if a parent with S1 and a parent with S4 have a child, that child has an equal chance of inheriting any of the four skintones.
Quick reference chart for the 4 Maxis skintones:
Alien skin is regarded just like a custom skintone by the game, which we will discuss next.
Custom Genetics (and how they work by default)
So, Maxis made us this wonderful game with an interesting genetics system. There are traits with different rules of inheritance, offspring can be carriers of recessive genes, so that's wonderful, right?
Well, they screwed up bigtime in one way: CUSTOM CONTENT. You see, custom content as it is made in body shop and imported back into the game, doesn't play nice with this genetics system.
Any piece of custom content made in body shop and tossed into the game is dominant over every default. It breaks down like this:
Custom hair: Not only is it always dominant, this means that if a child inherits this custom hair gene from a parent that is their sex, they will inherit that very hairstyle, not just a hair from the custom bin.
Custom eyes: Custom eyes are always dominant. They behave as if they were a level above the brown and dark blue eyes. Custom eyes are equally dominant with each other.
Custom skintones: Ignore the entire skintone spectrum and turn it into a dominant/recessive trait. Custom skintones are dominant and ANY default skintone is recessive. (Within the recessiveness, the defaults still follow the spectrum rule.)
Alien skin is treated as a custom skintone by the game. Now, it's not as noticeable with the aliens, because natural born in game aliens are the product of abduction, and most of the time, that means your alien babies have one allele for the alien skin and one for their human parent's. Since they are carriers of a normal skintone, half of their kids will have alien skin and half will have human. (Unless they find another abuctee's spawn to reproduce with.)
The rest of this tutorial will be about how to fix your custom content so it behaves how you want it to in the game. No more CAS sims with custom hair, eyes, and skin populating an entire hood with the same set of genes and no variety!
Chapter 3: Default Replacements vs. Custom Content
How Genetics Works in The Sims 2
What gets passed from parent to child in the game?
There are four different categories that are heritable in the game: hair, eyes, skintone, and facial traits (such as nose, chin, eyeshape).
Facial Traits
Facial Traits deserve a quick note because they actually follow the simple dominance/recessiveness rules we talked about in the previous chapter. So you often see the same traits popping up over and over again in the same family. The one small exception is when both parents have, say, a dominant nose. In The Sims 2, when there are two dominant alleles, it's a 50/50 chance which allele actually appears on the face of the offspring.
For a quick example of facial traits passing on, check the family tree for the Laurince legacy. Note the prominant nose that is passed on from the Gen 1 spouse to Gen 5 offspring, as well as the chin of the founder that still exists in Gen 7.
Hair
I'd like to talk about hair next, because it's the next simple. There are four hair color bins (excluding, for the moment, the custom bin): Black, Brown, Red, and Blonde.
Black and Brown are both dominant alleles. If an offspring inherits either one of these alleles, plus one for another hair color, they will still express their dominant allele.
Red and Blonde are both recessive alleles. They will not be expressed if there is an allele for black or brown also.
For alleles that are equally dominant, there is a 50/50 chance which trait is expressed. So, if an offspring inherits one Black allele and one Brown allele, there is a 50% chance they will have Black hair and a 50% change for Brown. An offspring with one Red allele and one Blonde allele has a 50% chance for Red hair and a 50% chance for Blonde.
This makes inheritance a little more complicated and a bit more interesting. Now, if you only gave your sims black and red hair, for instance, everything would behave like our tongue-rolling example in chapter 1.
Example: Parent with Black hair and an allele for Red hair (Bk r) x Parent with Red hair (r r)
Okay, that's easy enough. But the outcome gets a little more complicated to predict if you take a parent with an allele for each (Bk r) and cross them with a parent with Blonde hair (bl bl):
You can see how just making one or two genes equally dominant changes the amount of variety you can possibly get. And having people roaming around who are carriers is even more exciting!
Eyes
There are five Maxis eye colors: Brown, Dark Blue, Light Blue, Green and Gray. The way genetics works with eye colors is very similar to hair inheritance.
Dominant Eye Alleles: Brown and Dark Blue
Recessive Eye Alleles: Light Blue, Green, and Gray
Again, eye colors on the same level of dominance have a 50/50 chance of being expressed, if offspring inherits two different alleles from their parents.
Skintones
Skintones are determined entirely differently from the other categories. It's both simpler and more complicated, if that's possible.
You see, instead of having dominant and recessive alleles, Sims' skintones are on a spectrum from light to dark. There are four default skintones, which are often referred to as S1 (light), S2 (tan), S3 (medium), and S4 (dark).
An offspring's skintone is determined like this: a child can have any skintone between that of its parents, including the skintones of the parents. Each skintone in the possible range has an equal chance of being inherited. So if a parent with S1 and a parent with S4 have a child, that child has an equal chance of inheriting any of the four skintones.
Quick reference chart for the 4 Maxis skintones:
Alien skin is regarded just like a custom skintone by the game, which we will discuss next.
Custom Genetics (and how they work by default)
So, Maxis made us this wonderful game with an interesting genetics system. There are traits with different rules of inheritance, offspring can be carriers of recessive genes, so that's wonderful, right?
Well, they screwed up bigtime in one way: CUSTOM CONTENT. You see, custom content as it is made in body shop and imported back into the game, doesn't play nice with this genetics system.
Any piece of custom content made in body shop and tossed into the game is dominant over every default. It breaks down like this:
Custom hair: Not only is it always dominant, this means that if a child inherits this custom hair gene from a parent that is their sex, they will inherit that very hairstyle, not just a hair from the custom bin.
Custom eyes: Custom eyes are always dominant. They behave as if they were a level above the brown and dark blue eyes. Custom eyes are equally dominant with each other.
Custom skintones: Ignore the entire skintone spectrum and turn it into a dominant/recessive trait. Custom skintones are dominant and ANY default skintone is recessive. (Within the recessiveness, the defaults still follow the spectrum rule.)
Alien skin is treated as a custom skintone by the game. Now, it's not as noticeable with the aliens, because natural born in game aliens are the product of abduction, and most of the time, that means your alien babies have one allele for the alien skin and one for their human parent's. Since they are carriers of a normal skintone, half of their kids will have alien skin and half will have human. (Unless they find another abuctee's spawn to reproduce with.)
The rest of this tutorial will be about how to fix your custom content so it behaves how you want it to in the game. No more CAS sims with custom hair, eyes, and skin populating an entire hood with the same set of genes and no variety!
Chapter 3: Default Replacements vs. Custom Content