-------- Original Message -------- Subject: Morphometrics of small, variable specimens--embryos Date: Tue, 29 Mar 2011 10:28:14 -0400 From: [email protected] To: [email protected] Hello all, I am currently doing 2D and 3D analyses of midgestational mouse embryos. My sample is variable owing to ontogenetic variation. Genetic variation is very minimal, as my strains are mostly congenics, having practically identical genetic backgrounds but differing only at one or two loci. The specimens are also very small. First, for the 2D analysis, I am photographing freshly harvested and unfixed embryos in three different orientations (top, lateral, and "frontal" = palatal view), mounting in a petri dish of cold saline and photo'ing two separate times per view. Each set of images per specimen is landmarked twice, and all the data will be subject to an initial procrustes ANOVA to assess the relative strengths of the different effects of mounting, landmarking, genotype, and specimen. However, I expect, and experience shows, that a significant portion of the variance in the data will be due to mounting errors. The embryos are small and difficult to position. GPA will take care of rotational errors. But slight rotations out of the plane (pitch and yaw) will produce variation in the data that will look like shape variation. My hope is that by mounting and photo'ing twice, I will reduce pitch/yaw errors. Will the mean square of the mounting effect reflect the amount of those types of errors? If I can identify a PC that appears to capture pitch or yaw, can I regress the procrustes coordinates on that PC in order to remove those errors from the data? Thanks. Eric [email protected] University of Calgary Faculty of Medicine
