Correct option (B) There are at least two different alleles for the gene for height.
Explanation:
Genotype is the genetic composition of an organism, i.e., the combination of alleles it possesses. Every character in an organism is controlled by a gene that has at least two alleles that lie on the two homologous chromosomes at the same locus. These alleles may represent the same (homozygous, e.g., TT for height)or alternate expressions (heterozygous,e.g., Tt) of the same character. Thus, if genotype for the height of an organism is Tt, this means there are at least two, different alleles for the gene for height, one is T and the other is t.