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In cattle, two major gene loci affecting hair coat color are the Extension (E) locus and the Dilution (D) locus. The E locus dictates red vs. black color, and the D locus can make animals white. There are two alleles at each locus.

Purebred Angus cattle are black and only produce black calves when interbred; likewise, purebred Charolais are white (with red noses) and only produce white calves (with red noses) when interbred. When Angus and Charolais are crossed, the F1 animals are all smoky gray.

When F1 animals are bred to Angus, smoky gray and black animals are produced in a 1:1 ratio. When F1 animals are bred to Charolais, smoky gray, white and cream calves are produced in a 1:2:1 ratio (among the white calves half have dark noses and half have red noses).

When the F1 are interbred, F2 animals have been observed to be black, white, smoky gray (the most common color at 37.5% occurrence), cream, and red (the least common color at 6.25% occurrence).

Based on this information, which statement below is likely to be TRUE?

Photos a and c courtesy of A.D. Herring, b, d, e, f courtesy of J.O. Sanders. Created for Copyright 2016. All rights reserved.


Red is completely dominant to black at the E locus, and dilution is incompletely dominant to non-diluted color at the D locus.


There is complete dominance at both E and D loci, and there is an epistatic relationship between these loci.


Black is completely dominant to red at the E locus, and the D locus shows an incomplete epistatic effect on the E locus.


Black is completely dominant to red at the E locus, and non-diluted color is completely dominant to white at the D locus.

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