Final answer:
To determine if a normal-feathered chicken is a carrier of the recessive silky feather allele, a test cross is performed with a bird homozygous for the recessive trait. The appearance of offspring with both feather types suggests the normal-feathered bird is a carrier, while all normal-feathered offspring would indicate it is not.
Step-by-step explanation:
To determine whether a normal-feathered bird is a carrier of the silky allele, you'd perform a test cross. Specifically, you'd cross the normal-feathered bird in question (phenotype normal, genotype unknown - could be either homozygous dominant or heterozygous) with a bird that is homozygous recessive for the silky trait (with a genotype ss for the silky feathers). This is because if the normal-feathered bird carries the recessive silky gene, crossing it with a silky-feathered bird (which can only contribute the recessive allele for the trait) would produce some offspring with silky feathers. If the normal-feathered bird is not a carrier (homozygous dominant), then all offspring will have normal feathers, as they would all have at least one dominant allele for normal feathers.
If the offspring display a mix of both normal and silky feathers, then the normal-feathered parent is heterozygous (carrier of the silky allele). However, if all offspring have normal feathers, it indicates that the normal-feathered parent is homozygous dominant for the feather trait and does not carry the silky allele.