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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 Byers Monica Chu.
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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 Byers Monica Chu http://www.colby.edu/chemistry/CH217/Fish%20Page/Pictures/Species/three%20spine%20stickleback.JPG
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
F1 Marine stickleback Benthic Paxton Lake Stickleback F2 375 F2 progeny (289 unaffected : 86 affected) mednews.stanford.edu/story_images/stickleback.jpg
Table 1 • 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
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
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
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