Final answer:
Chromosomes were first identified in the late 1800s due to improvements in microscopic techniques. The Chromosomal Theory of Inheritance was established in the early 1900s, solidifying the role of chromosomes in heredity.
Step-by-step explanation:
Scientists first identified chromosomes in the late 1800s, thanks to advancements in microscopic techniques. It was during this decade that the term 'chromosome' originated from the Greek word 'chroma,' indicating something colored or stained. This was fitting, as the visualization of chromosomes was facilitated by staining techniques that colored these subcellular structures, allowing scientists to observe their behavior during cell division and meiosis. In the early 20th century, Theodor Boveri and Walter Sutton's observations led to the development of the Chromosomal Theory of Inheritance, which identified chromosomes as the medium for Mendelian inheritance.
Subsequent work by Thomas Hunt Morgan and his colleagues in the early 1900s, including the creation of the first chromosome map by Alfred Sturtevant in 1913, provided experimental evidence that supported the Chromosomal Theory of Inheritance, showing that chromosomes are indeed responsible for heredity. Moreover, by the early 1900s, specific characteristics, such as number, sizes, and shapes of chromosomes, were recognized as species-specific, further establishing the connection between chromosomes and genetic inheritance.