Inbreeding eventually can lead to problems in breeding.As we compound our good genes, and build upon them, we are also compounding the bad genes. Oversimplified yes, but basically this is what happens. The three arm thing like the last post.
How critical this inbreeding thing is in turtles I dont know.
In a clutch of say 30 eggs, there are X number of variables in each progeny. Same as with litters of puppies...X number of variables within a given litter. Some may have the recessive gene, others you may have brought it to the forefront, and made it now a dominant or dominant recessive gene.
Again...I can go on for hours about this, but this not being Genetics 101...I can say this...go ahead and inbreed your turtles, but be willing to remove the less that perfect ones from your breeding program. And half sister, brother is a better choice, called line-breeding...breeding for a particular trait. Risky as well, but not as risky.
It is 1 am...did any of this make sense?