Presentation on theme: "Evo-Devo: Evolutionary Development"— Presentation transcript:
1 Evo-Devo: Evolutionary Development DNARegulatory genes: code for signal proteins and transcription factor proteinsSP: target particular groups of cells for gene expressionRegulatory sequences: binding sites of transcription factors (enhancers, promoters).Structural genes: Activated by binding of TF & RSResponsible for producing phenotypic characters.
2 Dll expressionEn/Inv expressionEyespots on a butterfly wing
3 Homeotic Genes and Animal Body Plans Multicellular animals develop in four dimensions.3 spatial + timeEach cell has to have1. information: where it is relative to other cells2. where it is in the developmental sequence.Information provided by Homeotic genes (Hox genes)
4 Cells along these major body axes assume positional information during development (After Strickberger.)
5 Hox genes in Drosophila (body segmentation) Positional informationColinearity:1. Expressed first2. Anterior to posterior3. Greater quantity oftranscription factorsGene location in hox cluster
7 Hox genes provide information on location. Colinear Hox gene expressionHox genes provide information on location.1. The transcription factor from the first Hox generequired to express downstream Hox genes.2. The effectiveness in initiating sequential gene expression declines with distance.Paralogousand evolutionarilyconserved
8 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.
9 Hox gene products activate genes responsible for making a particular structure. Mutations in Hox genesbx, pbx, and abxMutation of Hox gene antpWings normally appear on T2Hox mutations change identity ofT3 cells to T2 cells.An extra pair of wings is produced.Ancestors of dipteran flieshad 4 wings.Identity of a head segmentchanged to that of a thoracicsegment
11 Hox gene diversification diversification of animals Hox paraloges (homologs): in everything from SpongeBob Squarepants to humans to fungi and plants (MADS-box genes).Therefore, Homeobox genes predate the origin of animals.
13 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 legsPaired appendages on body segments; open circulatory systemCrustaceansHexapodsMyriapodsAn onychophoran (velvet worm)Closest living relative of arthropods1 pr. unjointed legs on each of thesimilar body segmentsChilicerates
14 Evolutionary diversification of arthropods partly based on sites of Hox gene expression Hox cluster of 9 locifor all arthropodsabdA always expressed onventral side of segmentUbx and abdA not expressedin posterior segmentsEvolutionary change in wherea Hox gene is expressedMutation:legless abdominal segments
15 Homeotic genes and Flower formation C. 300,000 sps. of AngiospermsFour concentric whorls of modified leavesNormal order: sepals, petals, stamens, carpels