Salana very kindly wrote out this detailed information on another post. Very informative.
Roan or dalmatian guinea pigs have one copy of the "roan gene", technically the roan allele, and one copy of the normal allele of this gene. (One from mom, one from dad.) Whether the pig gets spots or mixed white and colored hairs depends on other genes that aren't important. Each pig passes on half its genes to its children, so each baby has a 50% chance of getting the roan allele from Mom and 50% chance of getting the normal allele from Mom. If Dad is also a roan (or dal), each baby obviously has a 50% chance of getting a roan allele from him and a 50% chance of getting normal.
Now, some pigs can have the gene without showing it, for instance (broken link removed) has no white and black hairs mixed together, and the black patches on her head are too large and in the wrong place to be dalmatian spots. However, she gave birth to a lethal (she was pregnant when I got her--another good reason to avoid pet stores!). The enormous amount of white hair she had (due to other genes, which don't cause problems) completely obscured any signs of her having the roan gene. So any white pig, or any pig with large amounts of white could be carrying the gene.
Basically, if both parents are roan (I can't see your picture, so I can't see whether the mother is or not) then each baby has a 1 in 4 chance of getting two roan alleles and being a lethal white, and a 3 in 4 chance of being a perfectly healthy roan or non-roan (normally colored). All lethals that I know of have the following problems:
- blindness
- one or more missing incisors
- complete lack of hair color
Other problems that I have known lethals to have include:
- deafness
- missing eyes
- missing incisors
- deformed molars
- teeth that grow in and fall out randomly
These are all problems that
long-lived lethals have...most of them are worse off and die shortly after birth. Nobody knows exactly why some live and some die, although there may be digestive problems involved (a related disorder in rats causes the affected rats to be missing nerves in their large intestines) and the tooth problems have to be caught and managed quickly. I have a lethal, Einstein, who had his first molar trim at 3 weeks of age and had already been syringe-fed for a week at that point. Einstein is now a year and a half old, and I know of two lethals older than him.
If you wind up with a lethal (or more than one), I hope you'll do the right thing and take care of them as long as they live. It's a commitment of time (syringe feeding, vet trips) and money (Critical Care, tooth trims) that most people who get into breeding without doing research aren't prepared to make.
Here's the thread of Einstein's medical history and vet visits. Even non-GL-members can read it.
https://www.guinealynx.info/forums/viewtopic.php?t=7156
