Which group of regulatory genes plays a crucial role in determining the identity and arrangement of body parts during development?

• A. Gene Therapy
• B. Homeobox (Hox) genes
• C. Recombinant DNA
• D. Epigenetics

Answer: (B)

Regulatory genes that set up the body plan by controlling where and when other genes are turned on during development are being tested here. The Homeobox (Hox) gene family is a group of such regulators that determine identity along the head-to-tail (anterior-posterior) axis. They encode transcription factors with a homeobox domain that binds DNA and activates or repress a suite of downstream genes, guiding each segment to become the correct structure. Their expression is precisely arranged in space and time, and the order of Hox genes in a cluster often mirrors their expression pattern along the body, a feature known as colinearity. When Hox genes are mutated or misexpressed, one body part can take on the identity of another, illustrating how these regulatory genes shape where each part ends up and what it becomes.

The other terms refer to concepts or techniques rather than a group of genes that patterns the body plan: gene therapy is a medical approach to deliver genes to treat disease; recombinant DNA is a lab method for combining DNA sequences; epigenetics covers heritable changes in gene expression not due to DNA sequence alone, which can influence development but does not by itself specify the positional identity that Hox genes do.