What is a genotype?
Genotype indicates genetic constitution with respect to one or more traits
Genotype indicates the genetic constitution, whereas phenotype indicates externally observed appearance with respect to one or more traits.
Let us understand this by taking a specific example of pea plant ( Pisum sativum ).
We may select 10 tall pea plants which appear tall on observation. All these plants are phenotypically similar , i.e. these have same phenotype.
However, all these plants may not be genotypically different , though looking similar on external observation.
Some of these plants may have genotype TT (homozygous ) or Tt (heterozygous) . These tall plants may be called pure tall or impure tall.
On selfing homozygous tall plants will produce only tall offsprings , whereas heterozyous tall plants will produce both tall and dwarf plants.