Question

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of

(A) the influence of environment on development.

(B) paedomorphosis.

(C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts.

(D) heterochrony

Short answer

(A) The option “the influence of environment on development” isfalse.

(B) The option “paedomorphosis” isfalse.

(C) The option “a change in a developmental gene or in its regulation that altered the spatial organization of body parts” istrue.

(D) The option “heterochrony” is false.

Step-by-step solution

Hox genes

The Hox genes are a set of DNA sequence appearing in the eukaryotic genome that are primarily responsible for the laying out body plans of animals. These Hox genes contain DNA sequences called the homeobox. The hox genes determine segmentation and appendages.

Explanation of option ‘(A)’

The hox genes are the sequence that affects organisms on the genetic level. The change in the limb bud that allowed tetrapod evolution did not occur due to the environmental changes.

Thus, the tetrapod evolution did not occur due to the influence environment on development.

Therefore, the given option is false.

Explanation of option ‘(B)’

The term paedomorphosis refers to the retention of features that occur in earlier stages of life in later or adult stages. The evolution of tetrapod is not an event related to paedomorphosis.

Thus, the tetrapod evolution did not occur due to paedomorphosis.

Therefore, the given option is false.

Explanation of option ‘(C)’

The changes in body arrangement appeared due to the alteration in the spatial arrangement in the hox genes. These changes altered the regulation and expression of hox genes, and hence, the tetrapod evolved.

Thus, the tetrapods evolved due to the changes in the regulation of hox genes.

Therefore, the given option is true.

Explanation of option ‘(D)’

Heterochrony is the change in the rate of development. The changes that caused genetic alterations in the hox genes are not a result of changes in the rate or time of development.

Thus, the changes in the hox genes did not occur due to heterochrony.

Therefore, the given option is false.