• Primary Plumage Color Determination (Extension Locus):
• In domestic chickens, the primary feather color pattern across body regions is controlled by the Extension ($E$) locus on chromosome 1.
• Allelic Series at $E$ Locus:
• $E$: Dominant Extended black (uniform solid black plumage)
• $E^R$: Birchen (black with silver/gold lace on hackle and breast)
• $e^b$: Brown (wild-type female partridge pattern)
• $e^+$: Wild-type (black-breasted red / Red Junglefowl pattern)
• $e^y$: Recessive wheaten
• Other Loci: Secondary patterning genes (barring $B$, silver $S$, mottling $mo$) superimpose patterns over the base established by the $E$ locus.

Correct option: (3) E