Many people new to Aussies may not take the time to learn about color genetics in the breed.    It is important though, as it does have something to do with the health of puppies produced.    The merle gene is a dominant one (M), while the solid colored body (tri, bi or self color) is recessive (m).  If you breed two merles together, even if they were the product of merle to tri breedings (Mm), about a quarter of their puppies could inherit the dominant merle (M) gene from both parents, making them MM.   These pups will have a very high chance of being blind and/or deaf, and are often more white in color than their siblings.   These are called "pattern white"  as they have more white than color or white markings in areas they should not, as per the breed standard (such as on the body).  The white markings themselves are not always the issue, other than they don't meet the breed standard for color and markings.  The exception is in pups lacking color pigment on or in their ears as they have a higher chance of being deaf.   The MM pups may have deformed or small eyes, or even no eyes at all.    Many breeders avoid this issue by simply never breed two merle dogs together.  Some MM pups are marked "correctly" but may still be deaf.   Breeding a merle to a solid color (tri, bi or self-color red or black) will usually produce normal puppies, and breeding to solid (mm) parents (tri, bi or selfcolor red or black) will produce all solid pups.   Some  Aussies also carry the gene for body white, which can occur in merle to tri or tri to tri breedings, and shouldn't be confused with pattern white pups produced in merle to merle breedings.  Those pups may not meet the breed standard, but they won't have a double dose of merle and any associated problems.  We also have "white head" in Aussies and MAS, which to date is a non testable trait.  It can produce mismark pups even in litters where parents are clear for the S locus spotting gene.

If you want to read more about merle, Mary Langevin has written a book and runs a Facebook group by the same name - "Merle - SINE Insertion from Mc to Mh - The Incredible Story of Merle".

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https://www.facebook.com/groups/245793505958325

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    It should also be noted that since merle is dominant over solid (black or red) that when you breed a solid (self black or red, bi or tri) to a merle, it is the MERLE dog that determines the color in the pups.  The solid parent can only produce solid pups (self color, bi or tricolor.)  And on a related subject, it is the mother who determines the number of pups since it is her body that releases a certain number of eggs. The male determines the sexes of the pups.  So if you breed a blue merle female to a black tri male, and get 4 males and 4 females, you  know the male determined the sexes and female determined the numbers.  And if there are 5 merles and 3 tris, you will know the merle parent (in this case the merle mother) produced the number of merles and the number of tri pups!

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   Red (B locus/brown) is a simple recessive to black, so solid reds (tri, bi or self red) will be recessive to black, and red merle is recessive to blue merle. A blue merle dog is actually genetically black, but with the dominant merle gene which reduces some areas of black to a silvery blue, which can vary from a very pale shade to a darker steel blue.   For a puppy to be red, it will be (bb).  A black puppy who is red factored, which means it is black but carries red is (Bb), and a black puppy who does not carry red is (BB.)  This is true of solid or merle pups.  Think of blue merle pups as black ones with the merle gene, and red merles as red pups with the merle gene. 

 

  The addition of copper or tan points and white trim is also inherited, but not related to whether the dog is merle or solid.  Aussies who have no copper  and/or white may equally meet the breed standard as those who have one or both. 

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     An Aussie should have color completely surrounding the eyes, and dominating their ears and the area surrounding it.   For more information on the color part of the breed standard for Aussies or Miniature American Shepherds.

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https://mascusa.org/breed/standard

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https://australianshepherds.org/finding-an-aussie/breed-standard/

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