Question

in what way are two alleles for the same gene different?
a. they contain completely different molecules of dna
b. they are found on complementary strands of dna.
c. they have small variations in their sequences of nitrogenous bases.
d. they are found at different locations on a chromosome.

Explanation:

Alleles are alternative forms of a gene. They are located at the same position (locus) on homologous chromosomes. They are made of DNA (so they are not completely different molecules of DNA as in option A). Complementary strands of DNA are part of the same DNA molecule (not what distinguishes alleles - so option B is wrong). Alleles have small variations in their nitrogenous - base sequences which can lead to different phenotypic expressions. They are located at the same locus on a chromosome (so option D is wrong).

Answer:

C. They have small variations in their sequences of nitrogenous bases.