The most common genotype for a Rusty Black is (Bb Rr), which is a heterozygous Black/Bronze base with one copy of the recessive red factor, r. However, Rusty Blacks can also be homozygous Black-based with one copy of red (BB Rr), or even heterozygous Black/Black-Winged Bronze-based with one copy of red (Bb' Rr). All three combinations exhibit a similar phenotype for the most part, but they produce varying results in their offspring.
The most common breeding to create a Rusty Black is a Bourbon Red crossed with a Black, which results in 100% Rusty Black.
When breeding heterozygous Bb-based Rusty Blacks together, the offspring could be: Black, Rusty Black, Jersey Buff, Barred Black, Bronze, Red Bronze, or Bourbon Red.
Breeding homozygous BB-based Rusty Blacks together would result in only three outcomes: Black, Rusty Black, and Jersey Buff.
The third combination, Bb'-based Rusty Blacks bred together, would produce offspring that include: Black, Rusty Black, Jersey Buff, Barred Black, Black-Winged Bronze, Harvest Gold, and Regal Red.
