Final answer:
The first known sketches of human chromosomes were drawn in 1913, creating the first chromosome map. Chromosomes were first visualized under a microscope with improved techniques during the late 1800s.
Step-by-step explanation:
The first known sketches of human chromosomes were drawn in 1913 by Alfred Sturtevant in Thomas Hunt Morgan's laboratory. These sketches were the first representation of gene order and relative distance on a chromosome, known as a 'chromosome map.' Chromosomes were first visualized under a microscope with the help of improved microscopic techniques during the late 1800s, allowing cell biologists to stain and observe subcellular structures during cell division and meiosis.