COLORS inheritance
Parti:

THE PARTI (SPOTTING) GENE IN COCKERS
The S genes - known as piebald 
There are three genes at this locus,

S which is solid or nonspotted.

The sp gene which causes the normal spots on 
cockers 
and xsp which restricts color
to the extremes, such as only on the head and 
around the tail. 
The two genes sp and xsp work together always producing a spotted dog.
 

The S genes work like this:

S - non spotted dominant to sp and xsp (does nothing)

sp - recessive to S but dominant to xsp (normal spotting)

xsp - recessive to S and sp (extreme spotting)
 

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