A section of DNA molecule that controls the shape of thumb is called genes.
Step-by-step explanation:
DNA is the molecule, contains genetic information, and is further broken into strands called chromosomes. These chromosomes further comprise of small segments known as genes.
These genes comprise different alleles that provide people different shapes of a thumb. An organism with two alleles of each gene is called a diploid organism as they get one allele from each parent. Whereas, in haploid organism, one allele of each gene is only present.