The genotype "Bb" could best be described as:

a. homozygous dominant

b. heterozygous

c. homozygous recessive

d. co-dominant

b. heterozygous

Explanation:

In a representation of a genotype, the uppercase letter means refers to the dominant allele while the lowercase letter refers to the recessive allele. If the genotype is composed of two uppercase letters is characterized as homozygous dominant, while if it is composed of two lowercase letters is characterized as homozygous recessive. Finally, if it is composed of one uppercase and one lowercase letter is characterized as heterozygous.