text: In polymerase chain reaction (PCR) experiments, the GC-content of short oligonucleotides known as primers is often used to predict their annealing temperature to the template DNA. A higher GC-content level indicates a relatively higher melting temperature.
  Many sequencing technologies, such as Illumina sequencing, have trouble reading high-GC-content sequences. Bird genomes are known to have many such parts, causing the problem of "missing genes" expected to be present from evolution and phenotype but never sequenced — until improved methods were used.