Final answer:
In a case of codominance, a chicken with a heterozygous genotype for feather color would display a phenotype with both black and white feathers, such as black with white speckles.
Step-by-step explanation:
When talking about codominance in genetics, it implies that both alleles for a gene are expressed equally in the phenotype of the heterozygote. If a chicken has a heterozygous genotype for feather color, where feather color is a codominant trait, the phenotype would display both colors. For instance, if the alleles are for black and white feather colors, the resultant phenotype would have both black and white feathers, possibly as black feathers with white speckles, similar to the first generation of chickens hatched by the farmer mentioned in your example.
In such a scenario where feather color is a codominant trait, if the farmer interbred the speckled chickens, the offspring's phenotype would vary depending on the genotypes of the parents, with some chickens potentially being solid black, solid white, or speckled, following a 1:2:1 genotypic ratio characteristic of a Mendelian monohybrid cross.