The mammalian genome, despite being confined within a small nuclear space, exhibits a non-random spatial organisation essential for establishing and maintaining cellular function and cell identity. Specifically, chromosomes and even specific genomic loci tend to occupy particular radial positioning (thereafter referred to as radiality), which is closely linked to their chromatin state and gene regulation.In this thesis, I present an optimised and streamlined version of the GPSeq protocol. This protocol leverages the controlled diffusion of restriction enzymes to digest chromatin from the nuclear periphery towards the centre and thus enables genome-wide mapping of radiality at unprecedentedly high resolution. Alongside this experimental advancement, I streamlined a user-friendly computation pipeline to support the broader study of radial genome organisation.Thereafter, I applied this methodology to address two key biological questions: 1) how two parental alleles are radially positioned in the nucleus and the functional implications of their positioning and 2) whether cell type-specific radiality profiles exist and their functional relevance.In the investigation of allelic radiality, we applied GPSeq to a hybrid mouse cell line that carries two distinguishable alleles and thus allows allele-specific analysis. I found that autosomal alleles display similar positions along the radial axis. However, upon X inactivation, the two X chromosomes showed striking differences in radiality. Unexpectedly, the inactive X chromosome was located more centrally relative to its active counterpart despite its compact and heterochromatic nature. This finding was validated using a FISH experiment and suggests a novel perspective on the mechanism of X inactivation, in which the inactive chromosome X does not rely on the repressive environment at the nuclear periphery to remain silenced but instead relocates inward, likely to be associated with the nucleolus, another repressive nuclear structure.Building on the prior knowledge on radiality, I further profiled five different cell types to explore cell type-specific radial genome organisation. Intriguingly, these profiles revealed distinct patterns amongst cell types, while cell lines of the same cell type but different origins showed high similarity. Examination of intrinsic genomic features uncovered consistent relationship between radiality and chromosome size, as well as gene density across cell types. Moreover, an exceptionally strong correlation between radiality with GC content was observed in all but one cell type, which showed only a moderate correlation. A gradual and dynamic change was also observed during the differentiation of stem cells into cortical neurons, reflecting the specification of radiality profiles during differentiation. These findings together support the hypothesis that radial genome organisation contributes to establishing cell identity, despite the nearly identical genomic sequences across cell types.