Question

Researchers suggest that an increase in the number of Hox genes a leads to reproductive isolation in all cases. b could explain the evolution of color vision. c allows for the evolution of more complex body patterns in animals. d results in the decrease in the number of body segments in insects. e does all of the above.

Short answer

The correct answer is (c). An increase in the number of Hox genes allows for the evolution of more complex body patterns in animals, as each Hox gene is capable of defining a particular structure.

Step-by-step solution

Understand What Hox Genes Do

Hox genes are a group of related genes that control the body plan of an embryo along the head-tail axis. After the embryo has divided into segments, Hox proteins determine the type of segment structures (e.g., legs, antennae, and wings in fruit flies) that will form on a particular segment. Hox proteins thus confer segment identity, but do not form the actual segments.

Eliminate Incorrect Answers

Now let's try to eliminate the incorrect options:a. Hox genes' contribution to reproductive isolation is not universally accepted and is the subject of ongoing scientific research, so we cannot assume that an increase in the number of Hox genes leads to reproductive isolation in all cases.b. Hox genes are not primarily associated with the evolution of vision or color vision. This leaves us with options (c), (d), and (e).

Determine the Correct Answer

Given that Hox genes define the types of segment structures that will form in a certain segment of an embryo, we can infer that an increase in the number of Hox genes would allow for more complex body patterns to form, as each gene would be capable of creating a unique structure. Therefore, option (c) appears to be correct. We can also eliminate option (e) because it suggests that all of the above statements are correct, which conflicts with our earlier findings. Option (d) is discarded due to it doesn't align with the known function of Hox genes since an increase would allow for more complex body patterns rather than reducing the number of body segments.

Key concepts

Embryonic Development and Hox Genes

Embryonic development is a critical period in an organism’s life, where a single fertilized egg cell transforms into a complex organism with specialized cells and structures. This process involves a series of highly regulated stages, including cell division, differentiation, and tissue and organ formation. An essential aspect of embryonic development is the establishment of the body plan, which includes the overall layout of the organism’s body structure.

During this process, Hox genes play an instrumental role. These genes serve as molecular architects, providing the blueprint that guides the formation of the body along the head-tail axis of the embryo. They help divide the body into segments and assign each segment's identity. Without properly functioning Hox genes, an organism might not develop the correct structures in the right places, leading to developmental abnormalities.

Hox genes, working alongside other regulatory genes, ensure that specific body parts form at the correct positions. This process is more than merely organizing segments; it involves coordinating the development of complex structures such as limbs, eyes, and internal organs. These genes are remarkably conserved across many species, highlighting their fundamental role in animal development.

Segment Identity and the Role of Hox Genes

Segment identity is a concept in developmental biology that refers to the individual characteristics and functions of each segment in an organism’s body. This is especially evident in segmented animals, such as worms, insects, and even vertebrates, where the body is divided into discrete units.

Hox genes are paramount in establishing segment identity. Each Hox gene corresponds to a segment, or a set of segments, and it tells that part of the embryo what to become—whether that's a wing, a leg, or an antenna in the case of insects. For example, mutations in Hox genes can cause body parts to form in incorrect locations, a phenomenon known as homeosis. This can result in an insect with legs where its antennae should be, revealing the importance of these genes in providing segmental identity.

In summary, segment identity is crucial for the proper functioning of all body parts, and it's the specific combinations and expressions of Hox genes that determine the identity and fate of each segment during embryonic development.

Complex Body Patterns and Hox Gene Evolution

The evolution of complex body patterns in animals is largely tied to variations and increases in the Hox gene family. Over time, as organisms evolved to possess more intricate bodies with various limbs and organ systems, their genetic frameworks also became more sophisticated. In this context, 'more sophisticated' means an expanded repertoire of Hox genes, which allows for greater diversification of body segments and structures.

The duplication and divergence of Hox genes are seen as one of the driving forces behind the evolution of complex body architecture in the animal kingdom. This gene expansion provides the raw material for evolutionary innovation. With more genes available, each can evolve to take on a new or refined role, leading to an incrementally more complex body layout with specialized structures.

The relationship between Hox genes and body pattern complexity is well-supported, suggesting that an increase in the number of Hox genes can allow for a greater variety of segmental identities leading to the evolution of more complex body patterns, which is observed across diverse lineages of the animal kingdom.