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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Eyespots on a butterfly wing
Cells along these major body axes assume positional information during development
1. Expressed first
2. Anterior to posterior
3. Greater quantity of
Gene location in hox cluster
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
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
C. 300,000 sps. of Angiosperms
Four concentric whorls of modified leaves
Normal order: sepals, petals, stamens, carpels