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Genetic and developmental basis of evolutionary pelvic reduction in threespine sticklebacks
Michael D. Shapiro, Melissa E. Marks, Catherine L. Peichel, Benjamin K. Blackman, Kirsten S. Nereng, Bjarni Jonsson, Dolph Schluter &
David M. Kingsley
Kelsey ByersMonica Chu
http://www.colby.edu/chemistry/CH217/Fish%20Page/Pictures/Species/three%20spine%20stickleback.JPG
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Vertebrate Limb Structures
• Highly varied
• In phylogenetically diverse sets of vertebrates, hindlimb structures are reduced or completely absent
• Little is known about the mechanisms underlying the genetic changes that lead to hindlimb reduction in vertebrate evolution
• Marine threespine sticklebacks
- prominent pelvic skeleton
- protection against predators
• Freshwater threespine sticklebacks- reduced or complete loss of pelvic structures
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F1
Marine stickleback Benthic Paxton Lake Stickleback
F2 375 F2 progeny
(289 unaffected : 86 affected)
mednews.stanford.edu/story_images/stickleback.jpg
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• One major QTL on linkage group 7• Four minor QTL on linkage groups 1, 2, 4, and 10 • Region near linkage group 7 accounts for a large amount of variance in pelvic structure• Presence of freshwater alleles decreased the average size of pelvic structures
Table 1
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Figure 1
Increasing the total number of benthic alleles at the minor QTL of linkage groups 1, 2 and 4 resulted in greater reduction of pelvic structures than the effects of a minor QTL alone
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Figure 1
• Tbx4 gene mapped to linkage group 1
• Pitx2 gene mapped to linkage group 4
• Pitx1 gene mapped to the area that seems to be the major controlling region for pelvic reduction
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Left-right assymetry in stickleback pelvic reduction
• Pitx1 gene in the mouse is responsible for hindlimb development
• Pitx1 knockout mice exhibit strong directional assymetry
• Directional assymetry observed in F2 progeny
-stronger development on the left side in 78% of fish with pelvic assymetry