Scientists first discovered chromosomes in the nineteenth century, when they were gazing at cells through light microscopes. But how did they figure out what chromosomes do? And how did they link chromosomes — and the specific genes within them — to the concept of inheritance? After a long period of observational studies through microscopes, several experiments with fruit flies provided the first evidence.
What is a gene?

Physically, a gene is a segment (or segments) of a chromosome. Functionally, a gene can play many different roles within a cell. Today, most scientists agree that genes correspond to one or more DNA sequences that carry the coding information required to produce a specific protein, and that protein in turn carries out a particular function within the cell. Scientists also know that the DNA that makes up genes is packed into structures called chromosomes, and that somatic cells contain twice as many chromosomes as gametes (i.e., sperm and egg cells).

But what were the key scientific discoveries that helped establish these principles? As it turns out, the connections between genes, chromosomes, DNA, and heredity were not recognized until long after researchers caught their initial glimpse of chromosomes. The following sections present an abbreviated summary of the major discoveries that revealed these connections.

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Photosynthesis is a process by which plants turn energy from sun into 1.___ or 2.___

Photosynthesis is a process by which plants turn energy from sun into 1._ or 2._