Alternative forms of a gene that influence the same trait and are found at the same location in homologous chromosomes are called :

a. alleles.

b. phenotypes.

c. genotypes.

d. codominant.

A. alleles.

Explanation:

A gene is a physical segment of DNA which contains the code for a particular protein determines the trait of an organism.

The genes are present on the homologous chromosomes in the form of two variants or the alternative forms called "Alleles". The position where these alleles are present on the chromosome is known as a locus.

The alleles show their effect only when the two form of alleles (one from each parent) come opposite to each other during fertilization.

Out of these two alleles, the allele which shows its effect is called the dominant allele and the allele which is suppressed in the generation is known as a recessive allele.

Thus, Option-A is the correct answer.

a) carbon, hydrogen

b) carbon, hydrogen, oxygen, nitrogen

c) carbon, hydrogen, oxygen, nitrogen, phosphorus

d) sugar

e) amino acid

f) nucleotide