Creating simple S3 objects to simplify code can be done using the following steps:

1. Create a constructor function:

SimpleGenome <- function( nchr=NA, lengths = NA){
 
 genome <- list(
 chromosome_count = nchr,
 chromosome_lengths = lengths
 )
 class(genome) <- append(class(genome), "SimpleGenome")
 return(genome)
}

2. Call the constructor to make new objects:

ecoli <- SimpleGenome(nchr = 1, lengths = c(4600000) )
bakers_yeast <- SimpleGenome(nchr = 1, lengths=c(12100000))