Genetics
A few interesting genetics studies exist for the twist-necked turtle (Platemys platycephala). Bickham et al. (1993) performed a small-scale cytological survey on the ploidy levels (number of sets of chromosomes) for somatic and gametic cells on a few specimens in Suriname. The authors examined multiple tissues (spleen, liver, blood, testis) of six specimens (five males, one female) and found cells contained various ploidy levels within and among individuals. One male individual even consisted of triploid-tetraploid cells. More genetic variation was found with respect to diploid (2n) to triploid (3n) ratio occurred among individuals than within individuals. Also, diploid cells exclusively participated in meiosis and subsequent sexual reproduction for males so balanced gametes and normal fertility occurred.
This is a rare event because of the limited viable polyploid individuals that occur in natural vertebrate populations. The lizard genus Lacerta and fish genus Phoxinus are the only other known examples of diploid-triploid mosaicism. Additionally, Platemys platycephala contains several combinations of ploidy level (x n) in various cell or tissue types. This phenomenon is known as mosaicism or chimerism. In a follow-up study Bickham & Hanks (2009) performed cytogenic analysis of the twist-necked turtle to determine how widespread this process is throughout South America and discovered normal diploid populations exist in Bolivia while variable mosaic populations persist in Suriname. Additionally, Darr et al. (2006) found turtle populations from French Guiana had increased triploid frequency compared to both Bolivia and Suriname. Several hypotheses were tested using phylogenetic data from mitochondrial DNA (mtDNA), but a high level of divergence was found for the three monophyletic populations.
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