Related Experiment Video
Updated: Jun 30, 2026
10:31
The Drosophila Imaginal Disc Tumor Model: Visualization and Quantification of Gene Expression and Tumor Invasiveness Using Genetic Mosaics
Published on: October 6, 2016
Microevolutionary support for a developmental hourglass: gene expression patterns shape sequence variation and
Tami Cruickshank1, Michael J Wade
1Biology Department, Indiana University, Bloomington, IN, USA. tcruicks@indiana.edu
Evolution & Development
|September 23, 2008
Summary
Maternal-effect genes show higher genetic variation within species and greater divergence between species than other developmental genes. This explains the "developmental hourglass" pattern in evolution.
Area of Science:
- Evolutionary Developmental Biology (Evo-Devo)
- Population Genetics
- Molecular Developmental Genetics
Background:
- Evo-Devo aims to integrate genotype-phenotype dynamics with microevolutionary processes.
- Understanding sequence variation in developmental genes is key to evolutionary insights.
Purpose of the Study:
- To analyze sequence variation across five gene classes in Drosophila early embryo development.
- To connect within-species genetic variation to between-species divergence.
- To investigate the "developmental hourglass" model using gene sequence data.
Main Methods:
- Comparative sequence variation analysis of maternal, gap, pair-rule, segment polarity, and segment identity genes in Drosophila.
- Examining both microevolutionary (within-species) and macroevolutionary (between-species) patterns.
Main Results:
- Maternal-effect genes exhibit 2-3 fold higher relative sequence variation within species.
- Maternal-effect genes show 2-4 fold greater relative sequence divergence among species.
- Findings align with microevolutionary theory predictions.
Conclusions:
- Relaxed selective constraint on maternal-effect genes allows wider exploration of mutational and phenotypic space.
- Maternal-effect genes broaden the "base" of the developmental hourglass, while later-acting zygotic genes narrow the "waist".
- Genes with both maternal and zygotic expression show the strongest evolutionary constraint, obscuring hourglass patterns.
Related Concept Videos
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...
02:05Gene Evolution - Fast or Slow?
The genomes of eukaryotes are punctuated by long stretches of sequence which do not code for proteins or RNAs. Although some of these regions do contain crucial regulatory sequences, the vast majority of this DNA serves no known function. Typically, these regions of the genome are the ones in which the fastest change, in evolutionary terms, is observed, because there is typically little to no selection pressure acting on these regions to preserve their sequences.
In contrast, regions which code...
In contrast, regions which code...
02:02Cis-regulatory Sequences
Cis-regulatory sequences are short fragments of non-coding DNA that are present on the same chromosomes as the genes that they regulate. These fragments serve as binding sites for transcriptional regulators, proteins that are responsible for controlling gene transcription and differential gene expression across cell types in eukaryotes. Cis-regulatory sequences can be close to the gene of interest or thousands of bases away in the DNA sequence; however, those sequences that are further away are...
02:32Position-effect Variegation
In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
02:37Gene Duplication and Divergence
The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.
01:24Evolution of New Traits in Microbes
Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...