Final answer:
Features associated with facultative heterochromatin include methylation at CpG islands in regulatory regions, trimethylation of histone H3 at lysines 9 or 27, presence of LINE-type repeated sequences in animals, and localization at multiple sites between the centromere and telomeres.
Step-by-step explanation:
Facultative heterochromatin is distinguished by certain chromosomal features that can change its configuration between a more open to a more condensed state, thus altering gene expression. One of the features associated with facultative heterochromatin is methylation at CpG islands, located in the regulatory regions of genes (option a). This methylation typically results in the silencing of the associated gene. However, it also relates to the addition of various chemical modifications to histones, which includes trimethylation of histone H3 at the 9th or 27th lysine (option c), influencing the chromatin structure and gene accessibility.
Facultative heterochromatin can also contain repeated sequences, such as LINE-type in animals (option b), and it is located at multiples discrete sites between the centromere and telomeres (option d). These regions are not permanently silenced like constitutive heterochromatin but can be transcriptionally active depending on the cell's needs and stage of development. The flexibility of facultative heterochromatin allows for differential gene expression which is crucial for development and differentiation processes.