Zebra Finch Lab Report

INTRODUCTION
The zebra finch (Taeniopygia guttata) is a model organism in neurobiology (reviewed in Mello 2014) and is the second bird to have its genome sequenced (Warren et al 2010). In this species, the existence of a polymorphism for a putative pericentric inversion in the sixth autosome was described in wild birds and also in a colony kept for research purposes (Christidis 1986; Itoh and Arnold 2005). As a consequence of this rearrangement, this chromosome exists in two alternative morphs: one submetacentric and the other acrocentric. The current evidence, based on classic mitotic chromosome analyses cannot rule a different basis for these morphological variants, such as neocentromere formation. A possible way to test if a chromosome segment was affected by an inversion is to analyze the pattern of synapsis and crossing over in

Almost invariably, bivalent 6 carried two MLH1 foci in homozygotes with no statistical differences between males (1.9 ± 0.06) and females (1.9 ± 0.03); instead, the number of foci was drastically reduced in male (1.1 ± 0.03) and female (1.3 ± 0.09) heterozygotes. In heterozygotes, most bivalents (85%) had one focus; when two foci were present they were more commonly observed in the female. Focus frequency distributions indicate that crossovers occur more frequently towards opposite ends of the bivalent in homozygotes, with one focus at the proximal region and another close to the telomere of the long arm (Figure 3). In heterozygotes, the preferred location of the distal crossover is maintained, but there is a clear increment of foci at 40-50 from the terminus compared to the same region in homozygotes (Figure 3). In the heterozygotes, no foci were observed beyond 40% from the centromere of the acrocentric element, therefore it is possible that one of the inversion breakpoints is located