Which method is used to analyze the karyotype?

The analysis of a karyotype is primarily based on examining the complete set of chromosomes in an individual's cells, typically during the metaphase stage of cell division. At this stage, chromosomes are highly condensed and can be visualized clearly under a microscope. By capturing a picture of these chromosomes, a cytogeneticist can assess their number, size, shape, and any potential abnormalities, such as structural rearrangements or aneuploidy (an abnormal number of chromosomes).

The other options relate to different techniques in genetics but do not directly pertain to karyotype analysis. For example, chromosome painting is a technique used to identify specific chromosomes or parts thereof and could provide additional information but is not the foundational method for karyotyping itself. Direct DNA sequencing focuses on identifying the specific sequence of nucleotides in a DNA molecule, which does not provide information on the chromosomal structure as a karyotype does. Gene expression profiling examines which genes are active under specific conditions, again not relevant for evaluating the karyotype directly. Therefore, the method of capturing a picture of chromosomes during metaphase is the essential approach to performing a karyotype analysis.