Chapter 19, Problem 1Q

Summary Introduction

To review:

The results and formulate a hypothesis for the role of a transcription factor in the two species. Also, assess whether it is an example of heterometry, heterotropy, or heterochrony.

Introduction:

Transcription factors are the proteins involved in the process of transcribing the DNA (deoxyribonucleic acid) molecules into RNA (ribonucleic acid). These factors can repress or activate transcription to regulate expression of a gene within a cell of an organism.

Heterometry is referred to the change in the amount of gene expression during the developmental stages of an organism. Heterotropy is termed as the evolutionary change in the spatial pattern of development. Heterochrony is defined as the change in gene expression timings and developmental rates of an organism. The figure shows the gene expression pattern for both species 1 and 2 over the course of time.

Figure: Change in relative units of a transcription factor with time.

Explanation of Solution

It can be clearly observed from the above figure that the two species are relatively different in terms of the duration of time taken for a transcription factor to remain high. In species 1, the duration of gene expression remains longer in comparison to the expression of a transcription factor in species 2. Thus, it is an example of heterochrony due to the differences in their timing of transcription factor’s expression.

Thus, it can be hypothetically stated that the differential timing of expression of the transcription factor causes the morphological difference between species 1 and 2. A longer period of high transcription factor’s expression in species 1 specifically leads to longer abdominal bristles in that species.

Conclusion

Thus, it can be concluded that the species 1 have a longer time of expression of a transcription factor as compared to species 2 and this an example of heterochrony. The morphological differences occur between the two species due to the difference in the timing of expression of the transcription factors.