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Evo-Devo : Evolutionary Development. DNA Regulatory genes : code for signal proteins and transcription factor proteins SP: target particular groups of cells for gene expression Regulatory sequences : binding sites of transcription factors (enhancers, promoters).

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evo devo evolutionary development
Evo-Devo: Evolutionary Development
  • DNA
  • Regulatory genes: code for signal proteins and transcription factor proteins
    • SP: target particular groups of cells for gene expression
  • Regulatory sequences: binding sites of transcription factors (enhancers, promoters).
  • Structural genes: Activated by binding of TF & RS
  • Responsible for producing phenotypic characters.

Dll expression

En/Inv expression

Eyespots on a butterfly wing

homeotic genes and animal body plans
Homeotic Genes and Animal Body Plans
  • Multicellular animals develop in four dimensions.
  • 3 spatial + time
  • Each cell has to have
  • 1. information: where it is relative to other cells
  • 2. where it is in the developmental sequence.
  • Information provided by Homeotic genes (Hox genes)

Cells along these major body axes assume positional information during development

(After Strickberger.)


Hox genes in Drosophila (body segmentation)

Positional information


1. Expressed first

2. Anterior to posterior

3. Greater quantity of

transcription factors

Gene location in hox cluster


Colinear Hox gene expression

    • Hox genes provide information on location.
  • 1. The transcription factor from the first Hox gene
    • required to express downstream Hox genes.
  • 2. The effectiveness in initiating sequential gene expression declines with distance.


and evolutionarily



Each Hox gene contains a highly conserved 180 bp sequence – the homeobox.

Codes for a DNA binding segment (aa sequence) in the transcription factor.

The transcription factors activate structural genes.

Structural genes produce structures appropriate for that location.

Mutations in Hox genes result in inappropriate structures for that location.


Hox gene products activate genes responsible for making a particular structure.

Mutations in Hox genes

bx, pbx, and abx

Mutation of Hox gene antp

Wings normally appear on T2

Hox mutations change identity of

T3 cells to T2 cells.

An extra pair of wings is produced.

Ancestors of dipteran flies

had 4 wings.

Identity of a head segment

changed to that of a thoracic


hox gene diversification diversification of animals
Hox gene diversification  diversification of animals
  • Hox paraloges (homologs): in everything from SpongeBob Squarepants to humans to fungi and plants (MADS-box genes).
  • Therefore, Homeoboxgenes predate the origin of animals.

Representative arthropods: What is the basis of their diversity?

  • 1 million sp. described; maybe 50 million still to be named.
  • Exoskeleton; segmented body (H –T – A) and segmented legs
  • Paired appendages on body segments; open circulatory system




An onychophoran (velvet worm)

Closest living relative of arthropods

1 pr. unjointed legs on each of the

similar body segments



Evolutionary diversification of arthropods partly based on sites of Hox gene expression

Hox cluster of 9 loci

for all arthropods

abdA always expressed on

ventral side of segment

Ubx and abdA not expressed

in posterior segments

Evolutionary change in where

a Hox gene is expressed


legless abdominal segments


Homeotic genes and Flower formation

C. 300,000 sps. of Angiosperms

Four concentric whorls of modified leaves

Normal order: sepals, petals, stamens, carpels