Question

Genes involved in the patterning of the body axis, that is, in determining characteristics such as neck length and appendage formation, are called a. small subunit (SSU) rRNA genes. b. Hox genes. c. metameric genes. d. determinate genes. e. none of the above.

Short answer

The correct answer is b) Hox genes, as these genes are responsible for the determination of body plan along the head-to-tail axis in the embryo including characteristics such as neck length and appendage formation.

Step-by-step solution

Eliminate irrelevant options

By understanding the biological terminologies, we can deduce that options a) Small subunit (SSU) rRNA genes, c) Metameric genes, and d) Determinate genes are not involved in the patterning of the body axis. We can eliminate these.

Choose the correct option

After eliminating options A, C and D, it should be clear that option b) Hox genes are involved in the body plan formation and thus responsible for characteristics such as neck length and appendage formation.

Key concepts

body axis patterning

Body axis patterning is a crucial process during the early stages of embryonic development. It involves the organization of cells and tissues to form the primary body plan, which includes the head-tail, dorsal-ventral, and left-right axes. Hox genes play a significant role in establishing this framework, serving as master regulators that turn on or off other genes to specify the position and identity of each body part. This precise regulation ensures that each segment of the body develops correctly, leading to the complex structures seen in mature organisms.
Without proper body axis patterning, an organism could have misplaced or duplicated body parts, highlighting the importance of this process in evolutionary biology.

neck length determination

Neck length determination is largely governed by the expression of Hox genes. These genes control the development of vertebrae in the neck region, leading to variations across different species. For instance, a giraffe's elongated neck is the result of specific Hox gene expression patterns that extend the growth of cervical vertebrae. In contrast, humans have a shorter neck due to a different set of expression patterns in these same genes.
The regulation of Hox genes not only determines size but also influences the shape and functional capabilities of the neck. Understanding this process provides insight into evolutionary adaptations and diversity among species.

appendage formation

Appendage formation refers to the development of limbs and other protruding body parts from the main body. This complex process is carefully orchestrated by Hox genes that dictate where and how these appendages should develop.
These genes ensure that arms, legs, wings, or fins grow at the correct positions along the body axis. The precise expression of Hox genes is crucial for the formation of joints, digits, and even the segmentation of these appendages. Any alterations in the normal patterns of these genes could lead to deformities or misplacement of limbs.
Thus, understanding appendage formation not only aids in evolutionary biology but also in medical research focused on limb regeneration and repair.

metameric genes

Metameric genes contribute to the segmentation of an organism, which is a fundamental aspect of animal body plans. These genes are responsible for dividing the body into repeated segments or metamers, which is evident in organisms like earthworms and insects. Hox genes are a subset of metameric genes, providing specific identity to each segment.
This segmentation is crucial as it allows for specialized regions to perform distinct functions, increasing the complexity and adaptability of the organism. The study of metameric genes has led to advances in understanding developmental processes and evolutionary patterns, showcasing the interplay between uniformity and diversity in biological systems.

SSU rRNA genes

Small subunit (SSU) rRNA genes play a critical role in the cellular machinery of all living organisms. These genes encode the RNA component of the small subunit of ribosomes, which are essential for protein synthesis. Unlike Hox genes, SSU rRNA genes do not participate in body axis patterning or the determination of body structures.
However, they are vital in maintaining cellular function and growth, providing the framework necessary for ribosomes to translate mRNA into proteins effectively. While they do not direct morphological development, their evolutionary conservation makes them valuable in phylogenetic studies, helping scientists trace the lineage and evolutionary history of organisms across broad taxonomic groups.