Instructions: Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Input: Abstract: Injection of homologous DNA sequences into nuclei of cultured mammalian cells induces mutations in the cognate chromosomal gene. It appears that these mutations result from incorrect repair of a heteroduplex formed between the introduced and the chromosomal sequence. This phenomenon is termed 'heteroduplex induced mutagenesis'. The high frequency of these events suggests that this method may prove useful for introducing mutations into specific mammalian genes.
Output:
Animal