BLACK - Black was the original color for the breed and for a long time, the only accepted one.  Yellow eventually became eligible for registration and most recently, chocolate.  All Labrador Retrievers begin as black dogs. 

 

The genetic make-up for black is a dominant trait and affects the dog's skin pigmentation, not just the coat.  The genetic combination for a dog with black skin & coat pigment is BB or Bb.  The dominant B takes over and is expressed as a black coat whether the dog's second color gene is another dominant B or a recessive b.  If the dog has a recessive b, it will not be expressed, but can genetically be passed on to the dog's offspring.

 

All other colors for Labs are a dilution or variation of a black pigmented dog with a black coat.

 

YELLOW - A yellow coat on a Lab is the result of a pairing of recessive genes on the E allele.  This means that the genetic combination for a yellow coat is ee.  A dog with a yellow coat can still be a black dog (BB or Bb), but a different portion of the genes comes into play and affects only the coat color - not the skin pigmentation.  So, a yellow Lab can actually be a black pigmented dog with a yellow coat.  The result would be a Lab with a yellow coat and black nose and paw pads ('points').  Such a dog would have the genetic combination of BB or Bb (black skin pigment) and ee (yellow coat.)

 

Keep in mind that yellow is recessive and requires an ee combination.  If one or both of the genetics is dominant (E), then the recessive yellow will not be expressed, but if one recessive gene is present yet hidden, it can be passed along to the offspring.  As an example, a black dog can be BB +EE, BB + Ee, Bb + EE or  Bb + Ee.   However, if it had ee, the coat would be yellow.

 

CHOCOLATE - A chocolate Lab is actually an all-black dog, both in skin pigment and coat color, but the full expression of the black has been diluted.  Chocolate is a recessive trait that is based on the B allele, so it has the genetic combination of bb.  All black on the dog, both skin pigmentation and coat, will be diluted from black to chocolate. 

 

CHOCOLATE with YELLOW coat - If a chocolate dog, which is has the skin pigmentation genetics of the double-recessive bb also has the double recessive coat color genetics of ee, then the dog will be yellow with chocolate nose and paw pads.

 

Using two litters, we can show how these genetics will make for surprising combinations in offspring color combinations. 

 

Mia x Sarge:  Black female and chocolate male.  They produced a litter with pups that are black, chocolate, yellow with black points and yellow with chocolate points.  How is this possible?

 

Mia:  Bb + Ee.  The B overrides the b, so Mia has a black coat, but she carries the recessive gene for chocolate (b.)  Her E overrides the e and therefore is not expressed as a yellow coat, though she can pass along the recessive e for a yellow coat.

 

Sarge: bb + Ee.  The double-recessive bb is expressed as a chocolate coat.  His E overrides the e and therefore is not expressed as a yellow coat, though he can pass along the recessive e for a yellow coat. 

 

So, any combination between these two parents is possible, depending upon which gene the parent dogs throw for each pup, since B, b, E & e are all present in the parents' genetics.

 

Snickers x Yukon:  Chocolate female and yellow male.  They produce an all-black litter.  This is because they have the following color genetics:

 

Snickers:  bb and EE

Yukon: BB and ee

 

Snickers cannot contribute an 'e' to match Yukon's, to result in an 'ee' or a yellow pup.

Yukon cannot contribute a 'b' to match Snicker's, to result in a 'bb' or a chocolate pup.

All pups will be Bb + Ee = BLACK

 

POP QUIZ:  If Snickers were bred to Sarge, what color(s) would the pups be?