Final answer:
According to the information provided, all chromosome types (autosomes and sex chromosomes) can be visualized using light microscopy techniques when stained with agents such as Giemsa stain.
Step-by-step explanation:
The question asks which of the chromosomes cannot be discerned by light microscopy. Through the use of staining techniques, such as Giemsa stain, coupled with bright-field microscopy, geneticists are able to visualize the distinct banding patterns of chromosome pairs. These techniques enable the observation of approximately 400-800 bands across all 23 chromosome pairs, which include both autosomes and sex chromosomes.
The use of light microscopy, which has variations such as bright-field and fluorescence microscopy, allows geneticists to identify each chromosome based on banding patterns, size, and centromere location. While historically many internal cellular structures and the detailed morphology of autosomes and sex chromosomes could be revealed with light microscopy, the question hints at there being an exception. However, given the information provided, it seems that all chromosome types mentioned can be discerned with light microscopy if properly stained and examined.