Rabbit Coat Color Genetics

It can be difficult to tell the difference, for example, between a broken orange (which is an agouti color), a broken orange otter (sometimes referred to as a tort otter) and a broken black tortoiseshell (tort, a self color) that has brighter orange fur. 

If you determine that both parents are self colors, then you know that the rabbit is a broken black tortoiseshell who just happens to have a brighter color of fur.  If the parents are agouti or otter, you must consider the other options.  To determine the true color, in this case, test-breed the questionable colored rabbit to a black rabbit (the best choice is a true breeding black, that is aa BB CC DD EE).  If the rabbit produces chestnut babies, it is an orange (the "A" is needed to make chestnut).  If it produces a black otter, it is an orange otter and if neither is produced (with a sufficient number of offspring to account for chance), then the rabbit is a broken black tortoiseshell (tort). 

Other colors are difficult to determine as well, such as the difference between a sable point and a sable point marten (the rabbit on the left is a sable point marten, the rabbit on the right is a sable point).  Again, if both parents were self, the rabbit would be sable point.  If either parent was agouti or otter, then the rabbit could be a marten.  A test breeding could help you make a determination in this case as well.

Another great use for understanding the a gene is in the development of otters.  I am particularly fond of black otters and hope to devote some space to their development in the not-too-distant future.  Because otters are rarer in Holland Lops (they were culled out as non-showable for years--now we want them back!), your first otter may very well be an otter carrying self ("A-a"). 

Your first goal would be to produce true breeding otters, that is, otters that have two at genes (at-at) and the correct pairs of the other color genes for the color you are attempting, of course.  You can tell from the chart a few paragraphs above that you cannot produce a true-breeding otter from an otter and a self.  You can get some true-breeding otters, though, from breeding two self-carrying otters (at-a).  But, only 25% of your offspring from two self-carrying otters will be true-breeding otters.  Twenty-five percent won't be otters at all, and that's easy to determine.  But of the otters, you will not be able to tell by looking at them which are the true breeding otters.  By watching their offspring, however, you will be able to tell whether they are true-breeding or not.  If an otter ever produces even one self baby, it is not true breeding.  (You can go to the chart and follow the "at-at" line across or the column down and you will not find one single "a-a" offspring.)

In case it is not apparent, let me specifically state that the advantage to having true breeding otters when you are developing an otter line is that you will more reliably produce otters.  You will need the greater numbers of otters to work with in improving their conformity to the standards.  Usually this improvement is done by breeding true-to-type black tortoiseshell back into your otter line (which are a-a, of course).  If you try to work with self-carrying otters, only half of your resulting offspring would be otter (on the average).  I recently had a litter like that with five kits and got no otters at all--how frustrating!  Had I a true-breeding otter, all of the kits would have been otters (100% at-a).