Each physical trait of an organism is produced by the instruction of a particular

Allele Pair/gene

Explanation:

The alleles are found on gene. Allele are the genetic material that are responsible for expressing any trait/characteristic in any living being.

For instance,

Suppose a red gulmohar flower has genotype "RR"

and a white gulmohar flower has genotype "rr"

Here , "R" is the allele for red color of flower while "r" is the allele for white color of flower.

Thus, each physical trait of an organism is produced by the instruction of a particular allele pair or gene.

age range would be the answer