An individual's genotype is the allelles which they have inherited (alleles are different versions of genes). An individual's phenotype is the characteristics that their genotype codes for. What a genotype looks like in the phenotype depends on whether alleles are dominant or recessive. Dominant alleles are represented by a capital letter and they are always expressed in the phenotype, even if there is only one present. Recessive alleles are represented by a lowercase letter and they are only expressed in the phenotype if two copies are present.Taking eye colour as an example: A is a dominant allele and codes for brown eyes, a is a recessive allele and codes for blue eyes. If an individual has genotype AA, they have a phenotype of brown eyes. If an individual has genotype Aa, they have a phenotype of brown eyes.If an individual has genotype aa, they have a phenotype of blue eyes.Other key words to look out for: 'homozygous' and 'heterozygous'.I can show an example using a punnet square using the whiteboard.