When a cell needs to duplicate, DNA strands are tightly coiled into chromosomes (chromosomes are made up of DNA and protein). Genes are certain stretches of DNA that code for a certain protein with a specific bodily function. On a chromosome, the location of the gene is called a locus.
DNA contains all the genetic material that decides a person's traits, such as hair color, eye color, etc. The DNA also passes on traits from the parents to the offspring, which is why children always have common traits with their parents. Genes carry the information needed to pass on these traits.
In summary, DNA, genes, and chromosomes are very similar in their 'composition', since genes are stretches of DNA that codes for certain proteins and chromosomes are made up of coiled DNA. Their functions are the same in the sense that they are all vital in passing on traits from the parent to the child, and therefore in determining the physical traits of the offspring.
Hope this helps! =')
