Which of these defines the term phenotype (with reference to a gene's alleles)?
the genetic code of an organism (i. e. both of its
alleles)
the actual appearance or characteristics of an
individual organism (ie the effect of its allele
combination)
a situation where two equally dominant alleles
produce a phenotype that combines both
characteristics (eg, blood type ab)
two or more alternative forms of a gene

Phenotype is : The actual appearance or characteristics of an individual organism (i.e the effect of allele combination ).

Explanation:

We come across differences shown by   individuals of same  species or we can say dis-similarity shown by offspring when compared to his/her parents .

When we cross parental generation , the gamete formation occur in accordance with Law of Segregation and then we get to see different combination of gametes that give rise to offspring with contrasting characters (In accordance with Law of independent assortment ).

After crossing we make conclusions by calculating the phenotypic and genotypic ratio of the cross .

Phenotype : It refers to physical expression of an organism or  The actual appearance or characteristics of an individual organism (i.e the effect of allele combination ).

Phenotypic ratio of Monohybrid cross is always 3:1 .

Genotype : Refers to genetic constitution of an organism .

Genotypic ratio of Monohybrid cross is always 1:2:1 .