Genetics



Genetics are often given a bad wrap - with most people thinking that they're too complicated to understand. I think it's a fair statement to make that the majority of guinea pig owners (and even breeders) don't have a good understanding of the genetics behind the breeds they either own or are trying to breed.

If you're just a happy 'piggy-slave' to non-breeding pets then you really DON'T need to know what their genetic make up is. But if you are planning to breed or have a registered stud, I think this is a really important bit of information to comprehend - even if you just grasp the basics. 

I'm not going to assume a basic level of understanding here, but rather explain things from the beginning in common terms with as many images as I can to make this as simple as possible. You can also get some more detailed genetic/inheritance background information on this page (it relates to plants, but the basics of dominance and recessive are there) OR if you do already have a good basic understanding, you might benefit more from a guinea pig specific e-book written by another brisbane breeder that you can purchase and download here



GUINEA PIG GENETICS

Guinea pigs make babies through sexual reproduction. This means that you need one male and one female to produce offspring. (please visit my Breeding Info page for more information on cavy pregnancy/birth/newborn care if you're looking for more of the 'nuts and bolts' type info ). 


When the guinea pig's body is making the reproductive cells (eggs for girls, sperm for boys), the usual 64 chromosomes (DNA make-up found in every cell in their body) are split in half to make the sex cells (which will contain 32 chromosomes). This means that when the guinea pig's sperm meets the egg, the two 'half' cells join and create the perfect amount of full, new DNA for the new baby .This also means that only half of a parent's genetic make up is passed onto their offspring. 

In this extremely simplified example above you can see that the mum's DNA consists of two different genes 'D' and 'd', whereas the dad is 'pure' - both of his genes are the same ('D' and 'D'). 

When the eggs are made by the mother guinea pig, half of them will be genetically capitol 'D', while the other half will be lowercase 'd'. When the sperm is formed by the father, they can be nothing other than capital 'D' as this is all he can offer genetically. This is why true, pure-breed animals will produce identical babies when paired together, and why cross-breed animals can produce a whole host of different babies depending on what genes they are carrying. 

This is when we get into the dominant genes and the recessive genes. Dominant genes mean just that - they dominate their corresponding recessive gene. This usually means that there only needs to be one copy of the gene at the cellular level to produce the physical appearance in the animal's coat (with some exceptions we can get to later). With recessive genes you need two copies to get that particular appearance in the coat. The example I've drawn below is for a rosetted (Abyssinian) coated guinea pig crossed with a smooth coat guinea pig. Rosettes are dominant in guinea pigs - so I've used a capitol 'R' to represent a rosette gene and a lowercase 'r' to represent the lack of rosette, or smooth coat. 



In the first generation we have a 'pure' rosetted guinea pig (RR) crossed with a 'pure' smooth coated guinea pig (rr). The genes are split in half to form the sperm and eggs and are paired up to produce 4 possible pairings - all end up being genetically half rosetted, half smooth (Rr). BUT - because the rosette gene is dominant, these babies will have rosettes in their coats, and will look a lot like a pure Abyssinian. (The rosette placement might not be as nice as on the parent guinea pig though due to the presence of the recessive gene/complicating factors from other genes)

If we were to then take two babies from the second generation and breed them together, we would get different results again. This time, because both of the guinea pigs in this pairing are genetically half/half (Rr), there are 4 possible pairing combinations that could occur: RR, Rr, Rr, and rr. The 'RR' baby would likely look just like it's siblings who are 'Rr' - so there would be no way to tell what it's genes were until it came time for it to breed. The baby with the 'rr' genes would look smooth coat like it's grandparent. This is how different breeds can 'pop' up in crossbreed litters. Only recessive characteristics pop up unexpectedly. Dominant genes are seen in the animals coat/colouring.

Dominant genes in guinea pigs include (but are not limited to):
* Rosettes
* Short hair
* Dark eyes
* Straight hair


Recessive genes in guinea pigs include (but are not limited to):
* Smooth coat
* Long hair
* Red eyes
* Curls


Partial Dominance

Long and short coat genes can act a little less clear cut than the simple dominant and recessive roles. Generally the short coat is dominant and the long coat is recessive. If you have an animal with hair that grows to the ground, that animal is guaranteed to have two copies of the recessive long-coat gene (which I'm referring to with a lowercase 'l' in the diagram below). It becomes less clear with the short-coat gene.

A pure short coat animal with two copies of the dominant gene - LL - (here we're using a capital 'L' to represent this  dominant gene) can often look exactly like a cross-bred half long-coat/half short-coat animal (Ll). BUT - the short-coat gene is not always completely dominant, and a lot of half/half animals will have telltale longer strands of hair on the lower half of their bodies while having short hair everywhere else.



In the pairing shown above we've taken a pure sheltie (long-haired guinea pig) and crossed it with a pure short-coated guinea pig. The resulting offspring will all be genetically half/half. They would likely either look just like their short-coated parent, or have a few wispy longer stands on their rumps.

If we then crossed two of these second generation guinea pigs, we would be left with 4 possible genetic combinations - LL (pure short coated), Ll and Ll (both half/half again) and ll (pure long-coated) - this animal would end up looking like it's grandparent. Again showing how recessive genes can pop up generations later.

Obviously the possible pairings are just statistical odds - it just means that if there were 4 babies born from the litter, chances are that 1 would be LL, 2 would be Ll and 1 would be ll. You may well get 4 babies who are all genetically LL, or all of any of the other combos. You could have a single litter who is ll... or 2 babies that are both Ll like their parents... you really have no idea which eggs and which sperm are going to meet.

We work out the statistical odds by using a probability grid (see below:). This will obviously look different for different pairings. For example if both parents were pure for long coats (ll x ll), you'll have a 100% chance of babies also being ll as the parents have nothing else but the long-hair gene to pass on.
Impossible Outcomes

There are many urban myths out there of offspring born to parents who could not have possibly produced their specific coat-type. For example, you cannot breed an abyssinian (RR or Rr) from two smooth coated guinea pigs (rr) - even if the smooth coat came from aby parents as they do not have the rosette gene to pass on.

Likewise, you cannot breed a short-coated guinea pig (LL or Ll) from two pure long-haired parents (ll). Nor can you produce a straight-coated animal from two curly parents (unless both parents had different curl-genes, not very common in Australia, but has happened in the past when imported pigs were paired with Australian pigs - this is something that would need a whole other page devoted to it). We will discuss basic curls and straight-coats below.





The Illusive Curl

I've always had a soft spot for the curly-pigs. Specifically the long-coated curlies like Texels, Merinos and Alpacas, but Rex pigs are gorgeous too! In AUSTRALIAN guinea pigs, the curly gene is recessive and the straight hair is dominant. This is how curly texel babies can be born to straight-coated sheltie parents. (You cannot get a sheltie from a pairing between two texels as texels have nothing but the curly gene to pass on to their offspring).

In the diagram below I have shown how it is possible to get texels and shelties from different pairings. For the purposes of this information I am referring to the dominant straight coat gene as capital 'S' and the recessive curly gene as lowercase 's'. In the first generation we have a sheltie who carries the texel gene (but would otherwise just look sheltie in appearance) paired to a texel. If you don't know the ancestry of your sheltie, a pairing like this would show you if he/she was carrying the texel gene. If the resulting babies were all shelties, you could assume that there were no recessive curly genes to pass on and your sheltie was just sheltie (obviously with the laws of probability you may not see a curly bub even when the parent is carrying the curl - so you would never be able to be 100% certain.)



In the diagram above we have hypothetically paired two of the sheltie-looking offspring from the second generation who both carry the texel gene. The results of a pairing like that would statistically produce 25% 'pure' sheltie (SS), 50% Sheltie (carrying texel) and 25% texel. Due to the complete dominance of the straight coat over the curl, you would not know which babies were genetically 'SS' versus 'Ss'. If any babies came out with curls though, you would be guaranteed that their genetics would be 'ss' for curl.

The above diagram could also be substituted for rex guinea pigs and smooth-coat guinea pigs (substitute the shelties for the smooth-coats and the texels for the rex).


(Two sheltie, texel carrier babies. Texel mum, sheltie dad)

Obviously the complexities of guinea pig genetics are a lot more intricate than I have explained here. You don't have only one genetic factor to take into account with each pairing, but countless subtle additional ones (body shape, type, coat density, colouring, rosette positioning etc). However, if you can grasp the basic fundamentals of the coat-type and the dominance and recessive nature of the genes it may help you in your future pairing decisions.


42 comments:

  1. I stumble upon your blogspot when i am serching about piggies genetic. I love your posts! keep it up. please follow my blog:)

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  2. Helpful- but I'm wondering if my piggies carry a dominant trait or if they're homozygous recessive. Which hair color trait is dominant? White or Black? And what's this Brown I'm seeing on my tri-color pig? I'm just wondering. Thanks to anyone that knows.

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  3. There's not actually a 'brown' colouring in cavies. It's either chocolate (from the black series) or one of the variants of the red series (Red, gold, saffron etc). When you get into colours it tends not to be quite as simple as just dominant vs recessive - it's usually interactions between lots of variables. There are some amazingly detailed colour-genetic websites out there that might help: http://pipsqueakcaviary.freeservers.com/custom4.html

    http://minifluffsrabbitry.weebly.com/cavy-genetics-101.html

    http://www.britishcavycouncil.org.uk/Resources/Cavy%20Genetics%20Article%20October%202008%20rev%20A.pdf

    http://www.webring.org/l/rd?ring=capitolbunniesan;id=1;url=http%3A%2F%2Fwebspace%2Ewebring%2Ecom%2Fpeople%2Fff%2Ffallsacre%2Fcavy-genetics%2Ehtml

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  4. I just wanted to say thank you for sharing your knowledge. For a very new cavy fancier your information is easy to understand and a great introduction to genetics.

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  5. Thank you so much for posting the information that you have posted about guinea pigs! It has been so helpful for me! I have a question for you. I have a female teddy guinea pig, she seems to have some rosettes so I think she might be crossed with abyssinian. I don't have a male teddy but I'm hoping to achieve one by breeding her with one of my other males. Can you tell which males would be more likely to achieve a teddy in the litter? I have abyssinians, abyssinians with long hair on their rump, peruvians, silkies with a little wave in their fur, and an american. Thank you so much for your help!

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    1. Hi, thanks for your comment. Not sure I can be of much assistance though, as I'm not sure how differently the 'teddy' genes work to our Australian 'Rex' genes. Here in Australia the 'Rex' curl is recessive. So there would be no way for you to know which of your straight-coated boars might possibly carry it. In that case I would say your best bet if you want another pig just like mum is to breed her to the aby boar your have, then breed a son back to her. If the teddy gene is recessive like the rex curl gene, this will give your best bet for replicating her coat. If the teddy curl is a dominant curl, it won't really matter who you choose, though I'd still stick to the aby to double up on the rosetting (if that's what you're looking for?).

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  6. In all these examples you were breeding the babies with each other. Is this common?

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    1. I presumed she was just using them for genetic examples. I don't think she really meant to breed sibling with each other.

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    2. thanks Fiona - you are correct. The images are purely examples.

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  7. I was trying to figure out how the satin gene fits in, is satin dominant or recessive? I love the satin texels and am looking to purchase one but want to know more about the genetics to try and get more satin texel babies. Thank you.

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    1. Hi Lisa - the satin gene is recessive. So you'll need both mum and dad to either be satin, or carry satin to get the effect in the babies.

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  8. I have two unrelated, buff coloured Rex (1 sow, 1 boar) but the lady who sold them to me said you can't get a pure Rex from breeding two Rex together. Everything I just read in your article seems to contradict that. Was she misinformed or have I misunderstood your article?

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    1. Hi Fiona. If the animals are australian rex-coated guinea pigs, then all you will get from a pairing between them is rex babies. They have no other coat-gene to pass on.

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  9. I just brought a new little family member today, Im unsure of what breed she is, But her front half is short haired and the back long ?i brought her from a pet shop and they aren't sure of her age or breed, will her front grow long hair like the back or will she remain half and half? It matters not, Im just curious.

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  10. My sheltie cross coronet and sheltie had babies. Would the babies be sheltie?

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    1. Do the babies have crests on their heads? (looks like someone has pushed their hair apart with their thumb!). If so - they will be considered Coronets. If not, then they'll grow to look sheltie.

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    2. Is it possible for an american white crest to be in the same litter as an american guinea pig...no crest?? Got my girls from Petco and she said they're sisters from the same litter but one has the crest and other does not. Love em both anyway, but curious

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  11. We recently bred two show quality TSW Americans and although got some good patching on two out of 3 offspring, both have what looks like a rosette or cowlick like area on their backs. Where does this come from...and should we breed the parents again...thanks for any light you can shed.

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  12. Hi, I think this is probably a throw-back fault called 'angel wings'? Hard to say without seeing the bubs. It has come from the parents. The babies obviously shouldn't be bred from, and if you want to get very strict - neither should the parents. But you could try each parent again with a different partner (but you run the risk of continuing the fault on in another line). If the parents are particularly good example of the breed and you don't want to loose their genetic contribution, then try the different partners.

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  13. I got a curly from an Abyssinian coat and a smooth coat!
    One was smooth, one was Aby, and one curly. Really neat!

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    1. this is definitely possible, and happens quite a bit in pet litters.

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  14. Hello, This is a very well thought and well put together. just two questions though, 1. is it bad if brother and sister are bred and 2. how do you know if a guinea pig is Rr or RR if it just looks the same? blood samples?

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    1. There's no way to know for sure the genetic makeup of pet guinea pigs, nor what recessive genes they might be carrying without test-matings. But to do so just for the purpose of curiosity isn't a good idea. And it's not ideal for a brother and sister to mate, but it does happen and the offspring are usually fine.

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    2. Dear Emma's bears, i have recently purchased an American boar( whose genetics are unknown) to breed with my purebred texel sows. I wanted to know if all of the offspring would have straight hair. Hope to hear back soon thanks.

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    3. Your chances are quite high that all babies born will just look the the dad - short straight hair. You'd only see curls if he carries the Rex gene somehow. But ideally if you want to breed more texel babies you'll need a texel boar.

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  16. Hi my friend has 2 Texels sows and was thinking of breeding to one of my 3 boars, 1 is a coronet, 1 is a chinchilla, and 1 is a Abyssinian and we are wondering which pair would be the better one and what will they look like?

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  18. Hello, I am quite a new owner of 2 guinea pigs, one american boar and an abyssinian sow. I am wondering what will their babies look like if they are to mate in the future. Thanks

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  20. I have got some quite cross bred bubs and I am trying to determine what they will look like. At the moment being new born they just have a smooth coat. So anyways to start with there grandparents on the mothers side were pedigree sheba and pedigree sheltie. So mum is genetically 50/50 sheltie sheba. And phsically has very long hair but the positioning of hair is like an alpaca being swept forward at the fringe and just two rosettes on either side of her rump. Obviously shes straight haired though ofcourse. Im unsure how you determine dominant and regressive genes for a sheba/ sheltie??. As for the father his genetics were unknown, but if i had to go by how he phsically looks i would assume that hes a smooth coat cross sheltie, Ll.

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  21. My guinea pig at 8 weeks was sold to me as a Peruvian. After a handful of months that has now gone by now and she doesn't have that long hair I'm wondering what breed is she then? Her hair is still short but a just a little longer and thicker then any of the American guinea pigs I've seen.

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  22. My guinea pig at 8 weeks was sold to me as a Peruvian. After a handful of months that has now gone by now and she doesn't have that long hair I'm wondering what breed is she then? Her hair is still short but a just a little longer and thicker then any of the American guinea pigs I've seen.

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    1. Hi Tina, the most likely reason for the slightly longer coat is that one of her parents was a peruvian (or long haired breed), but the other wasn't. Sometimes this mix of long and short haired genetics results in an incomplete dominance of the short gene, meaning that the cavy can sometimes have longer tufts on their rump with shorter hair over their face/shoulders.

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  23. Hello, what are the genes responsible or creating a cinnamon chinchilla. I have a sow who is and I've been doing a lot of genetic research lately for fun. Because wouldn't an agouti cinnamon be A-E-bbPPSS. So is there an allele that I am missing that causes the chinchilla effect? What would that be and is it dominant or recessive? Is it one of the C alleles?

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    1. Hi tehetra, I'm assuming by 'Chinchilla' colouring you mean 'agouti'? The colour genes are something I'm not very familiar with though, but the link above should help you out :)

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  24. Hi I have two guinaepigs ,both 8 months old.female piggie is an abbysian anguish and get coat is a darker shade of brown and the male is completely black.i want to know weather they could give birth to multi coloured pups.thaks.

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  25. Hi I have two guinaepigs ,both 8 months old.female piggie is an abbysian anguish and get coat is a darker shade of brown and the male is completely black.i want to know weather they could give birth to multi coloured pups.thaks.

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  26. If you were to breed a texel with another texel, is it guaranteed? If I'm understanding your examples, being a recessive gene, you'd have to know that both parents weren't carrying a dominant gene like short hair or rosettes. The chances of having even 1 out of 4 bubs appearing to be all texel is small. Is that right?

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    1. Hi CcMonroe, a guinea pig can't actually 'carry' a dominant gene. If they have a dominant gene - it shows in the coat-type by the very nature of being a dominant gene. But if you have two animals who look texel (long curly hair with no rosettes), then their babies should be exactly the same. There are always exceptions to the rule though, especially in animals of unknown origins as in Australia not all 'curly' coats are the result of a recessive gene, despite popular belief.

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