Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

Monthly Update sign up
Mailing List signup
Rediscovering Biology Logo
Online TextbookCase StudiesExpertsArchiveGlossarySearch
Online Textbook
Back to Unit Page
Unit Chapters
Proteins & Proteomics
Evolution & Phylogenetics
Microbial Diversity
Emerging Infectious Diseases
Genetics of Development
Genes and Development
Differentiation and Genetic Cascades
The Details of Gene Expression
Establishing the Gradient and Coordinate Genes
Responses to the Concentration Gradient
Homeotic Genes
Cell Lineage Mapping and C. Elegans
Fate Maps
Cell-Cell Communication and Signal Transduction
Conservation of the Homeobox
Conservation of the "Control Switch" Gene for Eyes
A Brief Look at Plant Development
Stem Cells
Cell Biology & Cancer
Human Evolution
Biology of Sex & Gender
Genetically Modified Organisms
Responses to the Concentration Gradient

Coordinate genes such as bicoid lay down the grand plan, so to speak, upon which the genes downstream will act. The pattern of the developing embryo arises as these downstream genes are activated or repressed.

Like many of the other coordinate genes, bicoid encodes a transcription factor; thus, there is a concentration gradient of a transcription factor. The next genes in this developmental cascade, the "gap genes," possess binding sites for this transcription factor. Gap genes are so named because mutations in these genes can produce larvae with "gaps" (missing several segments). These genes differ in how many bicoid binding sites they have and, thus, vary in their sensitivity to this transcription factor. Some gap genes will become active at
Figure 4. Coordinate, gap, pair-rule, and segment polarity genes
low concentrations of bicoid, while the activation of others will require higher concentrations. Due to the concentration gradient, different regions of the developing embryo will activate different gap genes.

Unlike the coordinate genes, the gap genes are not maternal effect genes. The activities of the embryo's gap genes (and not those of the mother's genes) determine the phenotype. Gap genes also encode for transcription factors, and these affect the transcription of genes that further refine the patterning of the Drosophila embryo (Fig. 4).

Back Next


© Annenberg Foundation 2016. All rights reserved. Legal Policy