Are the ultimate cause of alleles.
a. mutations
b. karyotypes
c. dna molecules
d. none of the above

Option A, Mutation

Explanation:

Mutation can cause the variation in a defined genetic set of an organism there by producing allele of varied types. However an allele is a variant gene. For example

A male flower has following allele – WW (representing dominant white color flower)

A female flower has following allele – ww (representing recessive blue color flower)

If these two flower mutate either through natural processes or though the mating, new species of flower with a different and unique genotype (allele set) is formed

for example a grey color flower with unique allele set - Ww

Alleles are carried on chromosome which expresses certain trait, variation in genotype also brings variation in allele's trait expression.

Hence, option A is correct

looks like the answer is     c     to me!