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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

  • 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

  • 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

Colinearity:

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.

  • Paralogous

    and evolutionarily

    conserved


    • 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

    segment


    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

    Crustaceans

    Hexapods

    Myriapods

    An onychophoran (velvet worm)

    Closest living relative of arthropods

    1 pr. unjointed legs on each of the

    similar body segments

    Chilicerates


    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

    Mutation:

    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


    MADS-box mutants (Hox genes)


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