# Lethal genetic combinations?



## Fantasia Mousery (Jul 16, 2011)

So, I've read a few times that there are some genetic combinations that are lethal (or otherwise not advisable), but every time I try to search for more info about it, I come up empty.
For example, that double red (Ay/Ay) is not possible, because the fetus will die in the womb and get reabsorbed. And someone also mentioned something about splashed x splashed.

Would anyone like to explain to me (and others) what lethal combinations there are, and what they can tell about them?
I think it's an important thing to be aware of when breeding, and it's a shame that there's not much info about it anywhere (or maybe I'm just too dumb to find it).


----------



## SarahY (Nov 6, 2008)

Splashed x splashed is safe, but variegated x variegated is lethal; double variegated babies are aenemic and die within a couple of weeks if not humanely culled. Rumpwhite is a lethal homozygous as well, babies that have two rumpwhite genes will die in the womb. Sex linked brindle (which we have in the UK although it is rare here) is another one; females brindles are born healthy but male brindles have curly white coats and will usually die, though I can't remember exactly why.

As far as I know, double variegated and sex linked brindle are the only lethal genes which produce babies that must be dispatched.


----------



## SarahC (Oct 3, 2008)

male brindles are born copper defficient and do not absorb copper after birth in the normal way.They are used in labs for the study of menkes disease.


----------



## Velvet_Meece (Apr 20, 2009)

Did someone mention reds being lethal too, babies with double dose of red are absorbed in the womb? or did i misread something


----------



## MojoMouse (Apr 20, 2012)

Yes, Ay is known as lethal yellow. It's the dominant gene for the red/fawn variety. Breeders commonly use agouti in these lines so that they get Ay/A heterozygous mice, which are viable.


----------



## Fantasia Mousery (Jul 16, 2011)

Thanks, all 4 of you. That's very helpful.
Aenemic means they lack iron, right? Those are the pale babies, yes?


----------



## Serena (Dec 29, 2011)

aenemic means lacking red blood cells. It can be due to iron deficiency, but there are other possibilities, too.
but they are pale, yes.


----------



## Fantasia Mousery (Jul 16, 2011)

Okay, thank you


----------



## SarahC (Oct 3, 2008)

MojoMouse said:


> Breeders commonly use agouti in these lines so that they get Ay/A heterozygous mice, which are viable.


Do they really though I wonder?Or is that just something that is oft repeated.I only breed fawn x fawn. Of course they don't breed true,I remove the argentes that are produced.I've had them 10 years without issue.


----------



## MojoMouse (Apr 20, 2012)

Well argente is just the PE agouti, so I'd assume you breed PE Ay mice? The homozygous Ay don't get born so you wouldn't see them. Your Ay mice would be heterozygous with A, with Ay being dominant. You'd also get argentes when you have A/A mice (with PE). The reason I think agouti (or argente) is a good match is because these mice have some yellow pigment which should ideally strengthen the colour, rather than a/a mice which have no yellow pigment. As to how effective it is, I don't know because I don't breed fawns. (BTW by fawn I mean Ay, red or black eye.)


----------



## SarahY (Nov 6, 2008)

SarahC was just saying that she doesn't breed argente to fawn, only fawn to fawn. There's no need to breed fawn x argente (or red x agouti) for safety or health reasons, as Ay/Ay are never born


----------



## MojoMouse (Apr 20, 2012)

I don't think I explained what I was trying to say very well.  I just meant that agouti (or argente) seemed to be preferred as the other gene, because of the yellow component, rather than just black. Even if she only pairs fawns with fawns, one of the genes has to be something other than Ay, or she'd get no babies. I'm probably still not explaining very well, but never mind. It's the middle of the night here.


----------



## SarahY (Nov 6, 2008)

Oh I see! Carry on :lol:


----------



## Velvet_Meece (Apr 20, 2009)

I was going to say, i breed red to red, my females often blow up and then nothing comes of it, otherwise they often produce quite small litters. Yet if i breed red to argente, or red to agouti i get lovely large litters with nice reds in too. So i can totally understand how the lethal gene can affect production, a lot of babies are never born leaving you with few or no babies.


----------



## Serena (Dec 29, 2011)

But don't Ay/Ay die really early on during the pregnancy? I remember something about a stage where they are no more than a few cells... So shouldn't the females remain slim if they were all Ay/Ay babies?


----------



## Velvet_Meece (Apr 20, 2009)

Maybe its something else then, unless the bodily activities cause a bit of bloat...i'm not sure, but there is definitely a different in successful litters from red x red pairings compared to red x other.


----------



## MojoMouse (Apr 20, 2012)

Velvet_Meece said:


> Maybe its something else then, unless the bodily activities cause a bit of bloat...i'm not sure, but there is definitely a different in successful litters from red x red pairings compared to red x other.


The reds that are viable have one dominant red gene, Ay, and one recessive non Ay gene, such as A or a. The A or a is "hidden" because Ay is dominant. Ay/Ay isn't possible. Therefore all the reds are Ay plus something else. The something elses are always hidden because Ay has the highest level of dominance.

The point being made before relates to whatever "other" gene occurs with the Ay, to make the mouse viable. You don't need to actually cross a fawn to another variety to get the other gene. I think this is where the confusion is coming in. Fawn to fawn (red to red) pairings still have another gene there. Some genes, such as agouti, _seem_ to work better with the reds. Black doesn't contribute much. That's the theory, but as to whether the second gene has a lot of influence, I'm not sure.

I'm sure someone else may be able to explain it better than I can!


----------



## sys15 (Nov 26, 2011)

has anyone produced lethal red/viable red heterozygotes? i'm curious about both color and health.


----------



## Malene (Jun 8, 2010)

Serena said:


> But don't Ay/Ay die really early on during the pregnancy? I remember something about a stage where they are no more than a few cells... So shouldn't the females remain slim if they were all Ay/Ay babies?


Willys K. Silvers writes: "Ay/Ay embryos are formed but display characteristic abnormalities at the morula or blastocyst stage and die early on the sixth day of gestation after the trophectoderm of the blastocyst has come into contact with the uterine epithelium, i.e., before implantation is complete."
http://www.informatics.jax.org/wksilver ... e2-1.shtml


----------



## Malene (Jun 8, 2010)

sys15 said:


> has anyone produced lethal red/viable red heterozygotes? i'm curious about both color and health.


A^y/A^vy would look like a red, as A^y is the top dominant (see the link in my previous post), with the same health problems that A^y and A^vy have.


----------

