A Study of Variation in Chicozapote (Manilkara zapota)
The chicozapote is an abundant and frequently dominant species of tree found in different types of tropical forests of the Maya region of Mesoamerica. The tree has been cultivated or semi-cultivated in the Yucatan Peninsula region of Mexico since prehistoric times.
It provides many useful products, including timber, chicle gum (sap), edible fruits, and medicine. In northern Yucatan and Quintana Roo this tree is found in a wide range of vegetation types, from semi-deciduous tropical forest to periodically inundated savanna and tintales.
Over this distribution, the life form of the tree varies widely. Forest forms are taller and have straight trunks, large fruits and large seeds. The savanna form is generally shorter, with a twisted primary trunk that splits into branches very close to the ground. This form also has smaller leaves, fruits and seeds.
We are studying the genomic DNA of 4 populations of chicozapote to determine if the phenotypic variation between the different populations is accompanied by genotypic variation. Genomic DNA has been extracted from desiccated leaf material of these populations. In order to remove individual variation and only compare differences between populations, the technique of bulked segregant analysis is used. In this method, DNA from each member of a population is combined into a single sample. This results in four samples representing the total DNA of the four populations. These bulks are amplified using PCR (polymerase chain reaction) and random primers. When a band difference is observed between populations with a given primer, DNA from each individual in the populations is amplified using that primer. Polymorphic loci are identified and scored for each individual. When a sufficient number of polymorphic loci have been identified, the data will be statistically analyzed to determine if there is a significant genetic difference between the four populations.