Ans. is 'b' i.e., Phenotype* To explain these terms, let us have a simple example, which we have learnt in our school.* A sweet pea plant can either grow tall or short. The plant grows tall if the plant has TT or Tt and the plant remains dwarf if the plant has tt. In this example, plant being tall and plant being short are the two phenotypes. Hence phenotypes are the external manifestations of a genome. Genotypes are genetic expressions of a trait. Just by looking at something, if we can comment whether the plant can grow tall or if the plant has to remain dwarf is called as genotypes. So there are three genotypes - TT, Tt, tt. What are alleles? T is one allele and t is another allele. So alleles are alternating forms of the same gene.* Genotype is the genetic expression of a trait* Phenotype is the physical expression of a trait* Alleles are alternating forms of the same gene - in the sense they differ by a few nucleotide sequences so that aminoacid sequences of the polypeptide chain gets affected minimally - so that the function of the protein gets affected either qualitatively or quantitatively.* Polymorphism is presence of multiple alleles at a single locus giving rise to multiple phenotypes, provided the prevalence of the alleles in a general population is more than 1%# For example, hair colour - we do not say only black hair is normal, various shades of brown and even white hair in a blonde person is normal. This is because of the presence of multiple alleles - an allele produces black pigment, many alleles to produces various shades of brown and then an allele which does not produce pigment - causing blonde hair.# In this example the last allele which has failed to produce the respective protein should be considered as a defective allele. But we consider it as a normal allele based on prevalence. As prevalence of the allele which can not produce the pigment is more than 1% in the general population, we call it as a normal allele.