Brandon Ortega

bortegafresnostate.edu

Speciation can occur when two populations with a common ancestral origin become genetically incompatible and thus reproductively isolated. Many scientists have attempted to discover and understand the underlying molecular and genetic mechanisms for speciation, which are generally thought to involve epistatic interactions between alleles unique to each population. The aims of this study are to locate and to identify the genetic loci and their pathways of interaction when the phenotype produced by this interaction is either inviability or infertility. The nematode species Caenorhabditis briggsae is useful for studying the genetic basis of species formation. In particular, F2 hybrid offspring of two strains (AF16 and HK104) display a delayed development phenotype, which suggests the possibility that an epistatic interaction between genomic loci produces this phenotype. Developmentally delayed individuals require one more day of development than their wild type siblings before reaching reproductive maturity, producing a fitness disadvantage. Thus, studying developmental delay can be used to identify the genetic basis of the trait that reduces fitness within hybrid individuals. This possibly represents a trait that could contribute to species formation. It has been shown that the developmentally delayed F2 hybrids are homozygous for AF16 alleles across a poorly defined portion of chromosome III. Thus, we propose that the developmental delay phenotype is a result of an epistatic interaction between an AF16 allele on chromosome III and an HK104 allele elsewhere in the genome. The identities of the genes involved remains unknown. I will phenotype AF16-HK104 recombinant inbred lines, which have already been genotyped at high resolution, for their ability to produce developmentally delayed hybrid offspring when crossed separately to AF16 and to HK104. With these genotype and phenotype data, I will perform genetic mapping to reveal the chromosome III locus involved in developmental delay. Defining this genomic interval is the first step toward the larger goal of identifying the interacting locus. Understanding the genetic mechanism producing the delay phenotype furthers science by illustrating how speciation occurs as a result of genetic divergence over evolutionary time.