(a) In poultry, the allele for feathered shanks (F) is dominant over the allele for clean shanks (f). A poultry farmer noticed that some chicks hatched with...

(a)(i) The genotypes of both parent birds are Ff (heterozygous). [1] Both parents have feathered shanks (dominant phenotype), yet some chicks have clean shanks (recessive phenotype ff). For a clean-shanked chick to appear, it must inherit a recessive allele (f) from each parent, so both parents must carry at least one f allele.

(a)(ii) The type of allele not expressed in the phenotype of a heterozygous individual is the recessive allele. [1] In a heterozygous organism (Ff), the dominant allele (F) determines the phenotype, and the recessive allele (f) is present but its effect is masked.

(b)(i) The genotype of a clean-shanked bird is ff (homozygous recessive). [1] Clean shanks only appear when no dominant allele is present.

(b)(ii) To produce a flock that breeds true for clean shanks within two generations:

1. Select clean-shanked birds (ff) from the current flock. These birds are guaranteed to be homozygous recessive. [1]
2. Mate these clean-shanked birds together (ff x ff). [1]
3. Since both parents can only contribute the recessive allele (f), all offspring will be ff and will have clean shanks. The flock breeds true because no dominant allele exists in the breeding stock. [1]

This is achievable within two generations because the farmer already has ff birds available in the flock.

(c) The difference between genotype and phenotype:

• Genotype is the genetic makeup of an organism - the specific combination of alleles it possesses for a given gene (e.g. Ff, FF, or ff). [1]
• Phenotype is the observable, physical characteristics of the organism that result from the interaction between its genotype and the environment (e.g. feathered shanks or clean shanks). [1]